89 sidekick turn lights/fan on, ecu increases rpm

[CHANCE]

Hi guys, I just joined & this is my first post. I know this topic has been beaten to death, but I don't know what to trouble shoot next. Here's what I have done so far:
Rebuilt computer with new caps.
no air/vacuum leaks.
just passed Cal smog, so idle, EGR, O2,Cat converter etc are all good.
CEL is not stuck on & it gives me DTC 12 when I put jumper in fuse box.
Tested TPS & it is in spec.
new cap/plugs/wires/rotor/filters/fluids.


So, when the headlights or heater fan are turned on, the computer increases the idle & there is a clicking sound from the TBI. I think this is either the Injector or the IAC.
My guess is there is a voltage regulator somewhere that is not giving the computer the correct constant voltage.
if there is, can I replace it or is there a pin on the computer I can feed a constant 5 or 12v to so it doesn’t know the lights/fan are on?


My car has the early gold computer.
The IAC is facing the passenger side, not the front of the car as in the pic at http://carfix.stufftoread.com/TBI-1w.jpg

With the heater & lights off, this is an excellent running,reliable 4x4-Thanks for your help!

[jtgh]

Your IAC is toast. ( with long review, sorry)
why?
the alternator must prouduce more current to match perfectly the current you added.
A/C load, HeadLights, fan, or 1000w silly amps.

this current loads the engine real heavy and the RPM's drop.
the ECU watches the RPM and is always ajusting the IAC to keep the idle perfect, despite the Alternator load, this is a full servo closed loop design.

on mine if you pull the connector on the IAC the RPM will rise and there is no longer any
rpm regulation ,just as you detail.

the coil is open or the IAC is jammed. (gunk or what ever)

(hoping your ECU is good)

you can even pull the top air hose and you can feel it modulate.
little pulses of air going in, towards the vacuum depression.

1: measures about 30 ohms or less on coil. its ok.
2: feel those pulses and pull the connector and see it change RPM.
3: last is to DSO (scope) the input and you will see a 2mS/3mS (5mS period) square wave on the input.
If you have NO square waves, ECU is bad or the wires to it are open.
4: Reseat the ECU green connector. (fat wire side) KEY OFF !

hope that helps.

PS; the square wave i shown, in on my fresh air page. (car will not idle or dies or floods)
cheeers

[nickdarchik]

I just went through the same ECU mix and match parts from two bad units to make a good one, Mine is also gold in color and gives a 12 code. The simple fix is to remove the diode isolator that feeds into the "electrical load" terminal of the ECU. (you had asked about feeding in 5 volts somewhere) this will eliminate the problem. You might need to increase the idle RPM a touch if at all. The diode isolator on my "90" is located above the ECU along the left kick panel its inside a dead end plug that has wires only on one end. One the side is a clip holding the cover shut. Open the cover and remove the diode isolator with a pair of needle nose pliers, it just plugs straight in. close the cover and your off and running.

Nick

[jtgh]

see road map.

if idle will no hold the idle controls are faulty.

IAC


Pin B6 and B15 , sends PWM signals to IAC ,
it is a closed loop servo, in fact the FSM has 2 pages telling how to test it.

more nfo ? just hollar....

[jtgh]

forgot to say, as almost always, the problem can be mechanical or electrical.
the IAC or other air ciruits can be bad.

the IAC has only so much command authority , if air leaks in too much (due to some other path) then the IAC and ECU together can not correct it.

it's like being in a sinking boat, and you just can bail fast enough.

here is my fresh air page:
it is for 8v , but the theory is the same. (except for the dash pot calib)

fresh-air

[CHANCE]

Nick & JTGH, I can't thank you guys enough. I removed the Diode Isolator & the car is perfect now. Not only did you guys save me a ton of $ & time, I am enjoying this car so much that I want to find another with a/c.

Chance

[jtgh]

We dont have one of those on ,91 +

thanks for tip.

[JGA]

Hi

I have an 89 that is doing the same. When I turn the headlights on the RPM increases about 100 rpm (or so) and there is a clicking sound from the throttle body. I have replaced the ISC twice and it still does the same. However, they we both used units.

So are you saying to remove the diode issolator? So what is making the clicking noise anyway? Also, what is the diode issolator for?

Thanks

[kick-fix]

89's have this samuria diode thing . i dont understand. but will lookinto

Zuwharrie.Com BBS - Index

is well known here.

any time you change load, and rpm goes nutz. id expect it to many things.



the draw is bad, i will correct it and repost it.
ITs a giant wired "OR" gate. if this or that go true, ECU is told to raise idle.
output is brown yellow to ECU.
inputs is all status of loads, HL,fan ,etc.

so what does it do?

obviosly it tells ECU to raise idle.

so , your car is working perfect. (blush) ( i will add this to my 89/90 diff page) growing.

one just needs to read the FSM ,for this (sorry dont have one, they are rare)
someone here will post the words. see it 1 time before here, someone....?

on 91 , only the A/C and P/S over load ,raises idle.

not true on 89/90

i never knew this. but is obvious.

but why.
my guess is ECU on this old buggy is too slow or the ISC just cant handle all the loads.

so unplugging it , has only 1 side effect.
idle may go below 800 rpm.



SEE ATTACHED DWG FOR DIODE GATE DETAILS.

The jpg is mod'd by me to show diode detaiis
the pdf (wrapped in zip ) is orig.

[kick-fix]

it is NOT an isolator, it is a logic gate.

instead of having 5 inputs to the ecu (ports were expensive then and all the connectors)
they put an OR gate in front.

conclusion:
Its a feature , not a bug.