Suzuki Forums banner

1 - 20 of 102 Posts

·
Registered
Joined
·
276 Posts
Discussion Starter · #1 ·
Hi to all and hope everyone is safe. Im trying to run again with my ISC (I have a second hand ISC now on truck but disconnected). But I kept my original ISC which I can test with battery voltage and plunger inside of it moves, works etc, And I get 12v at ISC connector pins with engine on, but when I connect ISC to connector it doesn't do a thing. What could be wrong? I've been running truck with ISC on plenum but disconnected, and I get my idle at 800 once warmed up via bleed screw. Car runs great, good power, no misfires or hesitation whatsoever. But what bothers me is that because of not using ISC, when going from P to R or D, RPM's drops to 400 because of no ISC (no regulation). Now throw in A/C which I recently installed. Like I wrote everything works fine, even with A/C: uphills, cruising, city traffic, heavy traffic etc.
What could be going on? Is there a telltale sign that lets you know for sure is you have a bad ISC? Could it be ECU? Im lost at this. Any light on the matter would be appreciated.

Cheers!!
 

·
Super Moderator
Joined
·
25,128 Posts
When you turn your A/C on, what does your idle do? Or if you turn your headlights on? The ISC is meant to raise your idle (on a warm engine) in both cases. Does it? Note that testing your ISC with 12v for more than one second, can burn it out. The ISC should have a resistance of 11-1 ohms across its terminal. You seem to be advising that while the ISC bench tests ok, you feel that it’s not working because of the idle of the engine - that may not be so, and there are other issues that can cause your idle to drop once you put a load on the engine. Is that why you’re making that determination??
 

·
Registered
Joined
·
276 Posts
Discussion Starter · #3 ·
When you turn your A/C on, what does your idle do? Or if you turn your headlights on? The ISC is meant to raise your idle (on a warm engine) in both cases. Does it? Note that testing your ISC with 12v for more than one second, can burn it out. The ISC should have a resistance of 11-1 ohms across its terminal. You seem to be advising that while the ISC bench tests ok, you feel that it’s not working because of the idle of the engine - that may not be so, and there are other issues that can cause your idle to drop once you put a load on the engine. Is that why you’re making that determination??
Hi Bex. Yes that is my assumption. And yes I have read about testing the ISC no more than one sec. I was always aware of, thx. No, with the installed ISC (when connected), my idle does not raise if ac or headlights are on. I will test the ohms which I have not. The worst in my opinion is when moving from P to D or R. Is almost a 400 RPM drop. One thing though. The installed ISC but not connected if engine is on, sucks a bit of air though air nipple. If its disconnected no air should be sucked? Unless is leaking due to being old etc? One big question, since ISC if offline I calibrated idle though bleed screw and I get 800 RPM after car warms up. If I had a gross vacuum leak, and if I close bleed screw all the way down, would engine turn on? It does not. Could there still be a gross vacuum leak and not turn on? Im gonna swap ISC and test ohms on both. What other factos could be dropping idle that much when theres a load, besides not using ISC?

Thx!!
 

·
Registered
99 Tracker, 5 door, 2L, 4x4
Joined
·
10,542 Posts
It appears to me that you do not have the right equipment for testing and "it seems" is not sufficient..
 

·
Registered
Joined
·
276 Posts
Discussion Starter · #5 ·
It appears to me that you do not have the right equipment for testing and "it seems" is not sufficient..
Ok, so what would the right equipment be to do proper ISC testing?

Thx.
 

·
Super Moderator
Joined
·
25,128 Posts
In the 16v, another sensor that would affect your idle would be the MAF - if there are leaks that the MAF does not ‘see’, I believe it would cause your idle to be low.
The testing of the ISC, for that one second with 12v, would show that the plunger is vibrating. If you shake the ISC, you should not hear any rattling (if you do, then the internal spring is broken). And you test the ohms across the ISC terminal. Other than that, I don’t know of other testing that you can do - and if the ISC bench tests ok, it would appear that the issue is elsewhere....it could, of course, be the vacuum hose to the ISC, the electrical wiring, the ISC driver in the ECU....but if all this tests ok, then perhaps it’s time to look elsewhere. By the way, the ISC driver, at least in my car, runs off the green ECU connector, pin 6, a light green/black wire. With the key on, there should be less than 0.5v on that wire - with the engine running, you should have 12v.
You also advise that you’ve been adjusting the idle screw in order to get 800 rpm warm idle. Before you initially started doing that, what was the idle you were getting?
So, questions: is your check engine light on with the key on and off when the car is running. Do you get a code 12?
What is the history of this ‘fault’ - did the car always run this way, or was some repair done or something, where this condition suddenly showed up?
Have you confirmed your engine timing with a compression test? If not, it’s a good idea to do so.
Have you confirmed your ignition timing and looked at your spark plug tips to see if engine is running lean?
Have you confirmed proper exhaust flow?
Others may have other suggestions.....
 

·
Registered
Joined
·
276 Posts
Discussion Starter · #7 ·
In the 16v, another sensor that would affect your idle would be the MAF - if there are leaks that the MAF does not ‘see’, I believe it would cause your idle to be low.
The testing of the ISC, for that one second with 12v, would show that the plunger is vibrating. If you shake the ISC, you should not hear any rattling (if you do, then the internal spring is broken). And you test the ohms across the ISC terminal. Other than that, I don’t know of other testing that you can do - and if the ISC bench tests ok, it would appear that the issue is elsewhere....it could, of course, be the vacuum hose to the ISC, the electrical wiring, the ISC driver in the ECU....but if all this tests ok, then perhaps it’s time to look elsewhere. By the way, the ISC driver, at least in my car, runs off the green ECU connector, pin 6, a light green/black wire. With the key on, there should be less than 0.5v on that wire - with the engine running, you should have 12v.
You also advise that you’ve been adjusting the idle screw in order to get 800 rpm warm idle. Before you initially started doing that, what was the idle you were getting?
So, questions: is your check engine light on with the key on and off when the car is running. Do you get a code 12?
What is the history of this ‘fault’ - did the car always run this way, or was some repair done or something, where this condition suddenly showed up?
Have you confirmed your engine timing with a compression test? If not, it’s a good idea to do so.
Have you confirmed your ignition timing and looked at your spark plug tips to see if engine is running lean?
Have you confirmed proper exhaust flow?
Others may have other suggestions.....
Ok Bex, as always very helpful and insightful. No rattling on the ISC, ohms showed 14 ohm tested 3 times, Need to check the .5v with key on, but I do get the 12V with engine on. MAF was verified and cleaned back in 2017 where I performed an engine rebuild. The other areas I will verify and report. No check engine light nor code 12, but I can retest for 12's again. My idle had always drop once on load (R or D) Many many things done in the past for improve performance, besides engine rebuild (coolant leak on cylinder head). I removed intake Mani to clean carbon from all passages including the EGR orifice going to exhaust, rechecked TPS pins for proper ohms all checked Ok. I have tried to seal air tube that goes from air filter to TB, the rubber connector is cracking and I try fix with RTV (maybe there is a leak there, but air leaks tend to raise idle not lower it on this engines right?). New oxy sensor installed in 2017, I do have the tiny tiny crack between runners on exhaust manifold. New plug, wires, dizzy cap and rotor. After engine rebuild compression tests have been done twice all in the right numbers (can do again) Timing I haven't checked since engine rebuild (will do again). Other than that I can't come up with anything. Will test and report.

Thx!!
 

·
Super Moderator
Joined
·
25,128 Posts
Just a reminder - any air leaks after the MAF - meaning that this is additional air that the MAF does not see, and therefore the ECU does not regulate for, will knock down the idle.

But, in looking at your first post, you’re advising that the idle drops when the ISC is NOT installed. So, what happens when it is?? The same thing?
 

·
Registered
Joined
·
276 Posts
Discussion Starter · #9 ·
I think is stays the same as in it does the same, idle drops the same. Now I have a new problem. My harmonic balancer broke so Im working on that first.
Cheers!!
 

·
Registered
Joined
·
276 Posts
Discussion Starter · #10 ·
In the 16v, another sensor that would affect your idle would be the MAF - if there are leaks that the MAF does not ‘see’, I believe it would cause your idle to be low.
The testing of the ISC, for that one second with 12v, would show that the plunger is vibrating. If you shake the ISC, you should not hear any rattling (if you do, then the internal spring is broken). And you test the ohms across the ISC terminal. Other than that, I don’t know of other testing that you can do - and if the ISC bench tests ok, it would appear that the issue is elsewhere....it could, of course, be the vacuum hose to the ISC, the electrical wiring, the ISC driver in the ECU....but if all this tests ok, then perhaps it’s time to look elsewhere. By the way, the ISC driver, at least in my car, runs off the green ECU connector, pin 6, a light green/black wire. With the key on, there should be less than 0.5v on that wire - with the engine running, you should have 12v.
You also advise that you’ve been adjusting the idle screw in order to get 800 rpm warm idle. Before you initially started doing that, what was the idle you were getting?
So, questions: is your check engine light on with the key on and off when the car is running. Do you get a code 12?
What is the history of this ‘fault’ - did the car always run this way, or was some repair done or something, where this condition suddenly showed up?
Have you confirmed your engine timing with a compression test? If not, it’s a good idea to do so.
Have you confirmed your ignition timing and looked at your spark plug tips to see if engine is running lean?
Have you confirmed proper exhaust flow?
Others may have other suggestions.....
Hi Bex, I jumpered for DTC's and I get 12's all the time key on and running. I went ahead and tested TPS for idle switch volts (I never completed Volt tests) but yes to Ohms all spec)
All done volts tests were Key on and engine on

pin 1 gry/yel wire: 0v
pin 2 (idle switch) blu/wht wire; 0v idle 5v off idle
Pin 3 TPS throttle angle grey wire: .5v to about 4v idle to WOT
pin 4 gry/red wire: 5v from ECU

I still haven't check the ISC green/black wire key on at pin 6 on ECU. The MAF sensor has not been inspected either. BTW I went ahead and checked mechanical timing when I replaced my harmonic balancer and all marks (cam and crank) line up accordingly. Now, since of 2 days ago I have a new problem. Car is stalling when braking and doing a turn. I then put in P and she starts again with no problems. No bogging, shaking, misfire etc. 🤷‍♂️

Cheers!!
 

·
Registered
99 Tracker, 5 door, 2L, 4x4
Joined
·
10,542 Posts
You have checked the ISC directly with the battery and it works, you have 12vdc at the connector but the ISC does not function. Now take a headlamp or marker light and connect to where you have 12vdc, does the bulb light brightly ??

If YES, the circuit can deliver the required current, if NO you have a bad circuit/connection.. All ways test circuits LOADED. You can have an indicated voltage but have no capacity to carry a load.
 

·
Super Moderator
Joined
·
15,401 Posts
Now take a headlamp or marker light and connect to where you have 12vdc, does the bulb light brightly ??
I would suggest you NOT use a headlamp bulb for this test, you need a test "load" that will draw a current similar to that of the ISC solenoid or you risk burning the driver transistor in the ECU.
 

·
Registered
99 Tracker, 5 door, 2L, 4x4
Joined
·
10,542 Posts
How many amps does a sealed beam headlight draw?

A typical low beam unit is a GE 4000 which specs out as 55W at 13V, so amps will be about 4.2A per bulb
These circuits are self protecting, what do you think happens when the sensor shorts, we would be changing many, many ECU's
 

·
Super Moderator
Joined
·
15,401 Posts
Let me start by saying that the ISC is listed in the FSM as 11~13 ohms - the expected current would be considerably less than 4.2A.

I also want to point out - on this particular system, the ISC is a solenoid which supplies only a portion of the air flow required by the idling engine, the remainder is supplied via a cold idle mechanism and an adjustable air bleed passage in the throttle body - when the system is correctly adjusted, the ISC is intended to operate at a duty cycle of approximately 50%, with the engine warm and idling at approximately 750 rpm.

On this particular vehicle, the air bleed screw has been opened up to allow the engine to idle without the ISC so the duty cycle is going to be lower than 50%, quite possibly low enough that a 12V lamp may not light.

I would suggest the use of either a duty cycle meter, an analogue volt meter or preferably an oscilloscope if one is available.
 

·
Super Moderator
Joined
·
25,128 Posts
Just as an aside, when reading the first few posts again, it appears you are saying that the idle drops 400 rpm when going from park to drive, with the ISC connected properly, and also without the ISC connected???? There are a number of reasons why this might happen, even with a working ISC. I’m wondering if we are concentrating on the ISC, when the issue may be elsewhere.
 

·
Registered
Joined
·
276 Posts
Discussion Starter · #16 ·
Just as an aside, when reading the first few posts again, it appears you are saying that the idle drops 400 rpm when going from park to drive, with the ISC connected properly, and also without the ISC connected???? There are a number of reasons why this might happen, even with a working ISC. I’m wondering if we are concentrating on the ISC, when the issue may be elsewhere.
That what im also suspecting. I closed up the bleed screw all the way and then did a cold start next day and car would not start. Is this a clear indication the IAC is not working? (I know IAC is useless after warm up so I know is not related to my initial problem) . Ok then I read somewhere here of another test for checking MAF providing there are no vacuum leaks, is disconnecting a hose at the air pipe and if MAF is working, it detects this and rpm should raise. Well mine does not. Ok, now I have random extra low idle in traffic while in a stop or traffic light. I then went ahead last night and took TB, MAF, and EGR off and cleaned (EGR was not packed in carbon, TB somewhat dirty and MAF average dirt) Today I Started her up a while ago and to prove IAC working/not working I closed bleed screw again and car would not start. Opened it up, started reved to 1500 but then idle went way down almost stalling. Shut her off then it finally rev to 800rpm. Seems like a combo of things. All this with ISC off. Could it be MAF is ok but fuel pump is not delivering right pressure thus not raising rpm when hose disconnected? I feel like Im reaching a dead end.
Ohh and all this with DTC connector jumpered and throwing 12's allll the time. 🤬🤬

Thx in advance.
 

·
Super Moderator
Joined
·
15,401 Posts
The fact that the ECU cannot maintain the idle speed is an indication that the IAC system is not working, which does not necessarily mean that the IAC valve is defective.

Do you have the factory service manuals for the vehicle - if you don't, download them from the link below ...
Rhinoman's Suzuki Service Manuals

The idle speed control system on this vehicle is a little unusual in that it flows air through three different passages - one is specific to the fast or cold idle used when the engine is first started, the second is the air bleed passage that you are fiddling with and the third is the system of hoses and the IAC solenoid valve - once the engine is up to operating temperature, the first passage should be closed, and only the second two in operation.

Under normal operation the IAC solenoid is constantly being "pulsed" (opened & closed) by the ECU to allow a certain amount of air to flow - ideally the valve will be open 50% of the time and closed the remaining 50% and the air bleed screw is adjusted to achieve this "duty cycle" with the engine at idle speed. This allows the ECU to both increase or decrease the air flow by varying the duty cycle.

It is important to note that an increase in air flow through the IAC will not always equate to an increase in engine rpm, engine load must be taken into consideration - for example - if electrical loads (lights, blower fan, etc.) are switched on when the engine is at idle, the alternator load increases and this can cause the engine idle rpm to drop, this is the reason the IAC system exists, to compensate by increasing air flow, which brings the idle rpm back to where it was before.

How does all of this help you solve your problem - it doesn't - but you need to understand how the system as a whole is intended to work, before you can determine which part of it is not working, and only then can you determine what needs to be done to fix the problem.

I would suggest you take a look at the various hoses and connections that connect to the IAC and make sure that they are all clear and allow air to flow through as the first step - if you have access to an analogue test meter, set it on a 12V DC scale (or the next highest) and connect it across the IAC valve, with the valve connected - what reading do you get? An oscilloscope would be better for this test if you have access to one and know how to use it.

I would like to think that if the problem were related to the MAF or the fuel pressure, other aspects of the vehicle operation besides idle would be affected, from what you say, this is not the case.
 

·
Registered
Joined
·
276 Posts
Discussion Starter · #18 ·
The fact that the ECU cannot maintain the idle speed is an indication that the IAC system is not working, which does not necessarily mean that the IAC valve is defective.

Do you have the factory service manuals for the vehicle - if you don't, download them from the link below ...
Rhinoman's Suzuki Service Manuals

The idle speed control system on this vehicle is a little unusual in that it flows air through three different passages - one is specific to the fast or cold idle used when the engine is first started, the second is the air bleed passage that you are fiddling with and the third is the system of hoses and the IAC solenoid valve - once the engine is up to operating temperature, the first passage should be closed, and only the second two in operation.

Under normal operation the IAC solenoid is constantly being "pulsed" (opened & closed) by the ECU to allow a certain amount of air to flow - ideally the valve will be open 50% of the time and closed the remaining 50% and the air bleed screw is adjusted to achieve this "duty cycle" with the engine at idle speed. This allows the ECU to both increase or decrease the air flow by varying the duty cycle.

It is important to note that an increase in air flow through the IAC will not always equate to an increase in engine rpm, engine load must be taken into consideration - for example - if electrical loads (lights, blower fan, etc.) are switched on when the engine is at idle, the alternator load increases and this can cause the engine idle rpm to drop, this is the reason the IAC system exists, to compensate by increasing air flow, which brings the idle rpm back to where it was before.

How does all of this help you solve your problem - it doesn't - but you need to understand how the system as a whole is intended to work, before you can determine which part of it is not working, and only then can you determine what needs to be done to fix the problem.

I would suggest you take a look at the various hoses and connections that connect to the IAC and make sure that they are all clear and allow air to flow through as the first step - if you have access to an analogue test meter, set it on a 12V DC scale (or the next highest) and connect it across the IAC valve, with the valve connected - what reading do you get? An oscilloscope would be better for this test if you have access to one and know how to use it.

I would like to think that if the problem were related to the MAF or the fuel pressure, other aspects of the vehicle operation besides idle would be affected, from what you say, this is not the case.
Hello Rhino. Hope all is well. The cold start IAC test was done out of curiosity (was done years ago proving it works as it opened at cold and then gradually closing as she warms, under the same set up: bleed screw opened and ISC offline). So If air bleed screw is all the way in and there are no illegal air entry with IAC working it should start and it doesn't. But all these tests haven been done with ISC (IAC to some) bolted to IM but not electrically connected. You are right about the MAF. I just gave her a good 25 mile test run with AC off and then on under 95F temps and she sped up on demand without any power loss. Plus there were no issues like yesterday, shaking when in park or at a stop and idle waaay too low.

As for the ISC testing I do have a digital Multimeter. I have pinched and disconnected air hoses and just last night I checked them and all clear as well as ISC air pipe. One thing though. Why there is vacuum at ISC nipple if ISC is electrically disconnected and when it was off the car I could not blow air through it? Thanks for the links. Im downloading them. Will keep on testing.
Thx to all.
 

·
Super Moderator
Joined
·
15,401 Posts
First - let me ask you this - why would a cold start IAC test performed years ago be of any significance now? From what you have posted much more recently, it would suggest that the cold start IAC is not working now, and, by the way, that is a completely separate issue from a non working ISC.

Second - can your digital meter measure duty cycle? Not all of them do - and if yours doesn't then it's no use for the tests I requested.
 
  • Like
Reactions: Bex

·
Registered
Joined
·
276 Posts
Discussion Starter · #20 ·
First - let me ask you this - why would a cold start IAC test performed years ago be of any significance now? From what you have posted much more recently, it would suggest that the cold start IAC is not working now, and, by the way, that is a completely separate issue from a non working ISC.

Second - can your digital meter measure duty cycle? Not all of them do - and if yours doesn't then it's no use for the tests I requested.
Indeed they are separate in form and function. Like I said I was curios about it and performed it back then and yesterday, thus discovering that (something to be addressed). But yes you are right, totally unrelated.
And no my DMM can not check duty cycle. I had gotten the this one Amazon.com: ZEUS new MST-2800B Intelligent Automotive Digital Multimeter tach/RPM/dwell: Automotive
but exactly testing ISC years ago to the best of my knowledge I discovered I could not set/check duty. Now it does work (the DMM). Which other you guys recommend?
 
1 - 20 of 102 Posts
Top