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Discussion Starter #1
So I have an '05 Forenza wagon, 28k miles, manual. Since I bought it with 3800 miles on it, it has had problems coming to an idle when coming to a stop. The RPM's drop past the usual idle of 900 - 1000, and often drop so low (below the 200 mark) that the engine shudders and the lights dim. The car has never died, but it's come close.

I had the high-idle problem early on, and had the re-flash done. That took care of the high idle (although it did it a few times after), but it has always had this issue when the RPM's wind down.

It's probably 60% of the time that it will do it. Hot or cold, it still does it. It's done it at high altitude and at 2000 feet. It will do it if I hold the clutch in, or put it in neutral. I can't pin down anything, and the car has NEVER thrown a code.

I've had the car in 6 times for this issue - and of course it doesn't do it during the 10 min. test drive by the mechanic. They won't do anything until they physically see the problem happen. I called Suzuki Customer Service, and got them to authorize a loaner for next week, so hopefully the mechanic will experience it.

Have you guys seen this at all? Any suggestions on where to look? Suzuki won't do anything until they can recreate the problem, but once they do, they're not going to know any more about it than the details I've given them. I've been to 3 different dealerships, and I know this isn't a Suzuki-designed car, but I'm not so far impressed by how Suzuki handles a problem. Every time I have a day off, I arrange to give up my car for the day... and nothing results.
 

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I never heard such a thing, but my guess is your timing is off but it gets off because something out side of the ECU control is causing it.
 

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High idle complaint is the only one I have seen, never a low idle.

You may have to hunt for a Suzuki shop with a really experienced tech who will know to bump up the idle stop on the throttle body if the usual diagnostics find nothing. The tech may want to consult with Suzuki Techline 1st though.

Has the throttle body been replaced?

Our 1st line of attack ( after verifying complaint ) is to reflash and if that fails we replace throttle body. There is a very very remote chance that your wiring harness that runs inside the left front fender well could have chaffing, but I don't know if any of those wires relate to engine controls.
 

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While not a Forenza, My Reno has that problem to the point that when I push the breaks turn and puss the clutch in at the same time it stalls.
I like the high idle problem, It makes a quick jump off the line more fun.
The idle drop I think is a electric problem, Almost like the alternator is too small to power the engine under high electric drain times. WOW i got lost on that one. Help me out tech guys, You know what I’m talking about.
 

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hi
first off did you get a lightened set of pulies? if so that might be your prob. i had a similar idle problem in my old honda. it could posibly be an ajustment on the throttle body or even a small vacume leak on one of the lines leading to or from the throttle body. this is a common prob when cars get older not so much on newer ones, a quick adjusment might be the fix.
 

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I would say your problem may have something to do with your alternator. I know when i had my other car, it would do that, my lights would dim, and want to stall. I took it to some places and they couldnt find anything wrong. So as it got worse and things began to flicker, my radio going off and resetting, and my rpms and speedometor shutting down and all my dash lights going haywire, thats when it started to die. It even drained my battery dry and had to get a new one with the new alternator. I would check into that, but it could be something else.
 

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sorry this is the first time I came across this post and sadly I dont know that I will be much help. As I have not seen a problem like this one yet.

But something quick you might ask your dealer is that after they did the reflash of the ECM did thay also:
Relearn the Idle and Relearn the Crankshaft postion sensor?
 

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Discussion Starter #9
Okay, an update - thanks to all who floated ideas and gave input. They've had the car for 6 days... they did re-create the issue. They cleaned the throttle plate (I think that's what he said), and it has made a big difference in smooth running - in fact, I would recommend this to anyone wanting smooth throttle response. My car had developed a hesitation around 3.5K RPM's, and that's gone now.

BUT - the idle dip is still there sometimes. When it happens, it's not as rough now that the trottle body is clean, but it still falls too low. I can still feel it shake the engine through my braking foot.

So, Melissa called their next suggestion - the alternator. SuzukiDon or SuzukiTech - can you tell me if there's a procedure for bench-testing an alternator? I want to get this resolved.

To answer above questions -- they did relearning procedures, there is no lightened pulley (no engine mods at all yet), and I, too, suspect electrical. TTGoth - try turning on your a/c and rolling windows down, then turn a/c fan to off. Then, while rolling up two windows, turn the fan dial from 0 to 3 or 4. You might get the same thing I got - shaking, straining, raw idle. Might be in the same boat as me, maybe.
 

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Schoolpsych, if you add an extra ground wire from battery to chassis with a large diameter quality ground wire, I think you will notice a major difference. I have done it and so have alot of people here, and trust me, it does make a major difference.
 

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Start with the altnernator test... An auto-electrical shop could probably do this for free if they're cool.

A good electrical shop may use the trick of placing a smaller pulley on the alternator to make it spin faster. On my old 91 escort they did that and the car idled about 100 RPM higher than spec which was pretty nice because it never dipped below that and of course made starting, accelerating, and electrical power a lot stronger.

On a whim sure the WATER level in your battery is always up. If you're in AZ your'e very dry and have extreme temps. This will slaughter batteries... If there's any less of a supplied charge then there's supposed to be, these kinds of problems can happen. On the other hand, if your battery happens to be one of those "self-maintenance" ones, then it's probably an alternator issue.
 

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Discussion Starter #12
Thanks for the thoughts- Jax, I think I will do an extra ground wire, just to see what impact that has.

I also considered the battery - good thought there too. It's an AC/Delco; I assume it's the stock battery. Supposed to be a 7-year battery, but as you said, extremes can be hard. The car did a cold-weather Idaho winter in 05-06. I was thinking about just upgrading to an Optima, but if my alternator's bad, that might be wasted money. Guess we'll check that out first.
I'll keep y'all posted - I'm sure someone else will find themselves up against the same issue.
 

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Ok, cleaning the throttle body helped, so you can forget the problem being basic electrical. This still points back to what I suggested which is to raise the "base" idle. Let me explain the method of idle speed control on todays cars.

We have a air control device usually referred to as a throttle body. All it does is control the airflow into the engine. It does this by opening and closing a large ~3" plate/valve. Usually this plate is directly controlled by a cable and the gas pedal, lately it is opened and closed by a electric motor (fly by wire).
If this plate is 100% closed no air gets into the engine and the engine will not run. So now we add a "throttle stop". That is simply a screw that keeps the plate from closing 100%. This screw is usually factory adjusted to keep idle no lower than 400rpm. Yes, all engines in proper tune will run at 400rpm. But hey, all cars I ever had idle at 700rpm or higher!

Yep , there is a another device that is on this throttle body/valve. It is a additional method of air control called a "idle air control" valve/solenoid. The car computer controls this. This metered valve routes air around the throttle plate. It can vary the rpm about 1500 rpm. This is what keeps the idle the same under most conditions. By the way, this idle control valve is a stepper motor, it is not very fast. Once your moving and the rpm is over 1200 rpm the computer closes the ICV.
What happens now when you take your foot off the gas? We rely on that mechanical throttle stop for a second or so until the ICV can catch up. If base idle is too low or ICV is not working then the engine can die.

Why did "cleaning" the throttle body help? As mentioned earlier it is a plate in a cylindrical housing. Various gunk from outside and inside the engine tend to cause deposits in this "bore/valve area". Eventually this cuts off enough airflow to affect engine "base" idle. Cleaning it restores it to normal airflow.

So given this explanation, what potential problems could we have that that cause idle rpm to drop? Dirty throttle valve? Fixed, made a improvement. Dirty idle control valve? Cleaned? don't know. Working correctly? Probably since idle is still in normal range except on quick stops. Has base idle been checked? Doubtful, very few techs know the basics that I just covered.

Since your repair shop did not correct the issue, buy yourself a long, small tip flat blade screwdriver. Open your hood, look where your throttle body/cable is, that is the plate linkage, In that immediate area you will see a very small screw in the throttle housing, probably with white or yellow tamper paint. You can take that long screwdriver you bought, drop it down thru the hole in the air cleaner duct and turn that screw clockwise 1/4" turn. Drive it for a few days to see how it does. If still not ok, give it one more 1/4 turn. If problem still not resolved after a 1/2 turn than i would replace the throttle body since either it is prematurely worn or the idle control valve is bad.

edit:
Just a note that ANY unmetered air leak such as a broken PCV valve/orifice/hose as mentioned in next post can cause higher than normal idle speeds. This whole topic applies to most any late model fuel injected engine.

DISCLAIMER

This whole procedure is frowned upon by all shops as it is usually not needed. Do not perform it until all other options have been exhausted.
If this "adjustment" is overly done, a check engine light may occur as well as no idle control at all if rpm is set too high. This post is for informational purposes only and you perform it at your own risk holding nieither myself or any employee of Suzuki responsible.
 

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Also check your PCV valve for functionality. According to the manual it's never supposed to fail, but that doesn't mean it can't. Take the plastic trim off the valve cover, pull out the PCV and shake it - if it rattles then it's functioning. A clogged PCV can make your engine "bog". You can clean it if you have to, but this is a $2 repair so it's another great place to start.

For the TB Every 10K miles or more, spraying some Carb Cleaner (any generic will do) all over the throttle plate also into the intake manifold will remove and prevent gunk from building up on those surfaces thus will lubricate the plate and unrestrict airflow into the combustion chambers. How does gunk get up in the intake mani? Partially some dirt particles coming up through the air cleaner duct, plus other crap that's recirculated into the intake manifold from the PCV valve.
 

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PCV on Reno/Forenza is a metered orifice built into the valve cover. It is not serviceable. You can clean it with solvent or replace the valve cover.
There is also a bullentin out about how some got out of the factory without the restrictor orifice. Those were obvious failures since the cars used a lot of oil and smoked fairly bad :)

I also see a lot of PCV HOSE failures around 40,000 - 50,000 miles on the 04-05 MY. The hose will get soft and collapse or actually break open. The hose was redesigned for 06 and later.

This is on U.S. cars, not sure about others.
 

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Wow, Suzuki had a lot of confidence in these cars when they started selling them didnt they? I'm honestly scratching my head 'cause the manual says to "inspect" the PCV system at a certain interval, but not much good in doing that if you "can't" replace the valve (?)
 

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Discussion Starter #17 (Edited)
So I just got back from an all-day drive, roaming northern AZ. Climbed 6000 feet in elevation over 100 miles, with the AC on and a passenger -- and I got just over 27 mpg. My numbers haven't been that good since I got the car. Clean those throttle bodies, people! Major results.

Unfortunately, the car still drops too low when falling to idle -- it just stumbles a little less because it's running better. There's still another culprit, I think.

I'll keep updating here as developments occur -- I think the next step the dealer wanted to do is look at the alternator. I'll keep you posted - thanks for the input.
 

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schoolpsych said:
So I just got back from an all-day drive, roaming northern AZ. Climbed 6000 feet in elevation over 100 miles, with the AC on and a passenger -- and I got just over 27 mpg. My numbers haven't been that good since I got the car. Clean those throttle bodies, people! Major results.

Unfortunately, the car still drops too low when falling to idle -- it just stumbles a little less because it's running better. There's still another culprit, I think.

I'll keep updating here as developments occur -- I think the next step the dealer wanted to do is look at the alternator. I'll keep you posted - thanks for the input.
Damn! where'd ya go, flag?

Thats damn good for going there or most places up North here. One time I got 31-32 mpg coming back from CA running so rich I couldn't even break 4k rpms cuz the engine would cut out. I dont know how the hell it happened either cuz I was cruisin 90+ the entire way.
 

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Discussion Starter #19
Yeah, drove up to Flag, went to Walnut Canyon, Montezuma's Castle, down through Oak Creek to Sedona -- playing tour guide.

The car stumbled more today than any day since I got it back.
 

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kinkyllama said:
Damn! where'd ya go, flag?

Thats damn good for going there or most places up North here. One time I got 31-32 mpg coming back from CA running so rich I couldn't even break 4k rpms cuz the engine would cut out. I dont know how the hell it happened either cuz I was cruisin 90+ the entire way.
We really like open roads. I got that doing a cruze down to San Diago. Open freewaythe whole way both ways
 
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