Idle prob just won't go away!

84porsche9113.2 · 06-19-2007, 12:41 AM

Okay, despite doing a lot of research here and tinkering with my car, I still have not been able to fix my low idle problem.

After a lot of research and poking around and fixing things, I've got the idle much better than before, but it is still not correct. Right now the idle is very predictable as to how it behaves even though it does not behave quite correctly. I am hoping that maybe the specific/predictable way it is behaving right now might be a red flag to someone who has experienced the problem before and/or might readily recognize how to fix it...

Anyway, right now what is happening is when the car is cold, and I start her up, she'll idle just fine a little above 1k rpm or so (start up idle is usually higher for some reason but only for a little while). After the cold idle, the car starts idling normally at around 850 for only the first few minutes of driving. After that, the idle will always inevitable drop and start to settle at around 500 rpms or so when I am at a stop. When the idles drop like this, there is nothing I can do to make the idle permanently come back to 850. Sometimes in a vain attempt to raise the idle, I will blip the throttle. This works to raise the idle back to 850 only temporarily. After the blip, the idle stasbilizes at 850 for only 5-10 seconds or so, and if I leave it idling for more than 5-10 seconds, it will again inevitably some how "settle" down to 500 rpms again. I can do this all the time right after cold start, blip it, see the idle go back temporarily normal, then after 5-10 seconds, watch it settle down to 500 rpms again. Always the case when the car is slightly warm.

This pattern changes completely once the car gets to normal operating temperature (first white 'tick'). After driving for 20-30 mins and the temperature comes up on the guage past the first white tick, then the idle always settles at 850 rpm (instead of 500 when slightly warm) and it never goes below 850. So in part it seems like this is a problem related somehow to the engine temperature. The problem always appears after start up from cold, and always goes away when at normal operating temps. The idle is always perfect after the car reaches normal operating temps.

I've done everything suggested in the posts including checking TPS position, ICV, looking for vaccum leaks, replace head temp sensor, ground wires, plug connections, etc. BTW, I know it is not an O2 sensor issue as I have a SW euro chip that disregards O2 input. Everything seems to check out so far but I can't fix the problem. I'm wondering if anyone has experienced a similar problem and/or solved it and can make any suggestions as to what to check next???

Would an exhaust leak cause this situation more so than an intake leak? (I'm just guessing)...

Thanks in advance...

Ned nyna 11 · 06-19-2007, 02:17 AM

The ICV is the prime suspect here. When the throttle closes the icv switch is connected. Get out your meter and verify, at the ICV terminals that the switch works.

Lo-tech next. Plug the ICV air in tube and see what happens when you start up. Note that when the ICV is out of the loop, idle speed is controlled by the bypass screw on the throttle body. If with the ICV disabled you tighten up this screw and choke off the air the idle speed would be limited by the air passing the throttle plate plus vacuum leaks. If you can stall the engine by closing the bypass, likely you have no vacuum leaks

84porsche9113.2 · 06-19-2007, 02:51 AM

Ned, thanks for the info! Well, I don't suspect the ICV only because I had it replaced maybe 5 years ago or so with a new one, and I only drive my car maybe 2k miles a year at most (weekend car, driven maybe once a month?). So there are very few miles on the ICV. Plus I know it hums and vibrates when there is power to it... I have also cleaned it out with wd40/carb cleaner, etc. I saw the factory procedure about connecting the center prong of the ICV to a 12V source and then alternately connecting the outside prongs to ground -- ICV valve should rotate to other stop each time. I've done this test a while back, but not recently. I figured since it is humming when i connect the harness, it must be working. . .

Since you suspect the ICV as the primary culprit, would you have any explanation why the ICV would appear to work properly when the car is at normal operating temps but not when slightly warm after first started? If there was a reasonable explanation to this question then it might point in the direction of a solution to this annoying problem....

I've also already made sure that the idle switch is making contact before the throttle valve opens after a specified dead travel of 1mm (per factory specs), so I'm sure it is not the idle switch either.

In any case, your troubleshooting procedure for vacuum leaks by attempting to stall the car makes a lot of sense and I'm very grateful and thankful for the wise advice, and it is something I never would have thought of on my own! That is something that is not mentioned in the manuals and the kind of advice I was looking for! I'll try it and report back with findings tomorrow.... Thanks again...

84porsche9113.2 · 06-19-2007, 03:05 AM

Ned, I forgot to mention and explain -- the reason I don't think it is the idle switch is because when I blip the throttle, the idle is temporarily stable at 850 rpm for 5-10 seconds before dropping down to 500 rpms. I believe that if this was a switch issue and the switch was not making contact at idle, the rpm's would be about 500 rpm's higher than normal idle. But this is not the case.

Also, when the car is at normal operating temps, the car idles correctly at 850 rpm. That means 'normal' idle is correctly set at 850. If the idle switch was not closing at idle when the car was warm, then the idle would be higher around 1350, not dropping to 500 rpm... It's also relatively easy to test this since if one lightly pushes on the throttle linkage to release the idle switch, rpm's should rise by about 500rpm's before the throttle plate even opens...

My guess is something other than the switch or ICV is causing the idle to drop when the car is slightly warm, but after searching for so long, I just don't know what it could be.... Will report back after trying your vacuum leak test... Thanks again!

Ned nyna 11 · 06-19-2007, 03:05 AM

It's more important to figure what's causing the problem than to figure out at this time why it's doing it.
As I said, eliminate the icv as a possible issue by plugging the tube.

84porsche9113.2 · 06-19-2007, 08:53 AM

Ned, I just tried your low-tech procedure this morning and I am unable to stall the car with the idle screw all the way in and idle valve blocked off. The car runs pretty terribly with the idle valve blocked off, and screwing the idle screw all the way in makes it run even worse, but won't stall it. seems like I am getting around 100rpms or so with the idle screw completely in.

I've checked all the hoses, tightened down the intake manifold bolts, tightened all the hose clamps, etc. I've also used propane directed via a long hose and inflatable toy nozzle. All to no avail.. Is there a better way to troubleshoot vacuum leaks? Or do I now need to get a professional to do it by using one of those smoke machines or something like that?

Ned nyna 11 · 06-19-2007, 09:02 AM

With the ICV plugged, adjust the idle speed using the bypass. Set it to around the desired speed and then go for a ride and check idle speed both cold and hot.

84porsche9113.2 · 06-19-2007, 09:12 AM

Ned, it doesn't seem like I'll be able to properly adjust the idle speed to 850 with the ICV plugged.

With the ICV plugged, it is running at arond 250 rpm's or so even though the idle screw is pretty much backed out all the way out. There is no more room for adjustment or to raise the rpm's to 850 or so.

In fact this is typical of my car. Even before these tests the idle screw was always set backed pretty much all the way out (I used the idle adjustment procedre by bridging the test jacks), and I was still getting low idle when slightly warm even with the screw backed all the way out.

Porsche_monkey · 06-19-2007, 09:25 AM

Could your mixture be wayyyy off? If it was too rich you would need a lot of air to idle.

84porsche9113.2 · 06-19-2007, 09:32 AM

PBH, perhaps this might be the case. But I don't have a CO tester and I'm trying to fix things w/o having to buy one or take it in for that. I've never adjusted the mixture using the allen screw on the AFM.

Anyway, if the mixture was way off, do you know why the car would idle properly when at normal operating temps but not when slightly warm??? That is what puzzles me.

I do have an adjustable FPR. Right now it is set to around 38 psi with the vacuum hose pulled off. I could experiment with lowering the fuel pressure...? Would anyone suggest this given my symptoms?

By the way, does anyone have an idea what the average going rate should be for a mechanic to test CO and set the air/fuel mixture?

84porsche9113.2 · 06-19-2007, 09:37 AM

PBH, the other weird thing is how the idle "settles" after startup. It seems like the standard procecedure after startup from cold is the rpm's increase to slightly above 1k rpms. Then it will slowly mellow out to around 850 rpms after a minuite or so. If I just sit there in the car, the idle is perfect for around 3-4 minuites or so. But then it will slowly and gradually drop over a period of about 1-2 minuites by several hundred rpms (maybe it is really not as low as 500 but more like 650-700 or so). And after that, it seems the idle remains low until the car gets back to normal operating temps, at that point the idle is always okay.

If it was a rich fuel issue then, why is the idle okay for a few minuites in the beginning? Is the fuel mixture getting richer as the car gets warmer? Also why would the problem go away when hot? Does the car use more fuel when hot so the idle is okay then???

Porsche_monkey · 06-19-2007, 09:45 AM

You are correct. And if it was that rich it would show in driveability.

You need to figure out why the screw is all the way out.

Since you have a SW chip you might consider emailing him.

84porsche9113.2 · 06-19-2007, 09:54 AM

Well, SW reads these forums and I don't believe it is a problem with his chip, but with my car. I was having these problems before I installed his chip. So being that I don't think it is an issue with his chip, I wouldn't want to contact him about it directly since he's not really obligated to help me fix my idle problem.

But if he's reading this post and wants to volunteer any info on what it might be, I'd be more than happy to try out any suggestions or fixes which he or anyone else might have.

PBH, seems like you are saying it is not "normal" for the screw to be all the way out. If that is the case perhaps my AFM is not working properly? What does it cost to calibrate these things or verify it is correctly calibrated? I've taken it out and saw the spring under there. Also the contacts do look a little tarnished. But my problem does go away when the engine is hot...

PBH, if you are saying the idle screw should not normally be all the way out, then the next logical conclusion to me, would be that the AFM is not properly calibrated or working properly? But the problem here is I am not aware of any procedures on how to test this or make sure the AFM is working correctly. Does anyone have any info on this?

Porsche_monkey · 06-19-2007, 10:36 AM

I only suggested Steve because he frequently responds to this kind of issue, and he is extremely knowledgeable. I doubt his chip is the issue.

The other detail is the adjustable fpr. I have no idea how that affects mixture on this car, but Steve would know.

And, no, I do not believe it is normal for the screw to be all the way out at idle.

What if you blocked off the ICV and drove the car for a while, or wire it to be shut all the time? If you still have an unstable idle then you've eliminated the ICV.

Ned nyna 11 · 06-19-2007, 10:44 AM

Can you check that the bypass passage is not plugged up?

It's not difficult to get the AFM and filter out of the way as a unit and get room to work.

Blow a little air through the orifice or snake a wire.

I would so this before getting into the AFM

84porsche9113.2 · 06-19-2007, 11:16 AM

Ned, a while back I took out the idle adjustment screw and cleaned the orifice. It was very dirty with black soot. I only used carb cleaner and q-tips though but I did remove the AFM and rubber boot to gain access to the orifices as well as clean the throttle plate very thoroughly. I can stick a blow gun in there and use my air compressor to try blowing it out. Will that work? I didn't blow air because I thought it looked clean enough when I used carb cleaner and q-tips, but I can try it just to be sure and since it's not that hard to do. I'll try that tonight and let you guys know the results later...

One question, if the ICV is getting the air from before the throttle plate, this means the ICV is getting metered air, correct? What about the air going through past the idle adjustment screw? Does this mean that both the air going through the ICV and the idle adjustment screw needs to open the barn door? Steve mentioned that sometimes in order to get cars to pass emissions people would tighten the barn door spring. I'm wondering if that's an issue here.

PBH, steve told me as long as the FPR is correctly set at 38 psi w/ the vaccum hose pulled off, and if it is a linear rate FPR (which I believe it is), it should run fine with his chip.

84porsche9113.2 · 06-19-2007, 11:25 AM

PBH, i'm not sure what you mean by blocking off the ICV and driving the car. As I said, if I block of the ICV, the car will run terribly at only 250 rpms or so. So you are saying to drive it like that?

Are you saying that the car should run and idle perfeclty fine with the ICV blocked off at 850 rpm? All I know is that mine doesn't because I am at 250 rpm with the ICV blocked off and the idle screw backed all the way out.

I don't think I'd just want to block off the car and run it at 250 rpm all the time.... If it was running at 850 rpm with the ICV blocked off, then I would do it.

I'm sorta not understanding something here. Are you saying that on normal cars with the ICV blocked off, it should be idling normally at 850 rpm?

Also, if most cars CAN run normally with the ICV blocked off and just using the bypass screw to control idle, then what is the purpose of the ICV????

Porsche_monkey · 06-19-2007, 11:34 AM

I assume you've done all this:

Porsche_monkey · 06-19-2007, 11:39 AM

I believe you should be able to get the the car to idle at 800 rpm with the ICV blocked off.

If you can't get above 250 rpm with the ICV blocked off, try unplugging it. It should stay in that position and you will be able to tweak your idle to 700-900, and drive it like that, to see if the ICV is the problem.

Maybe someone can confirm the correct position of the ICV when the jumper is in place, is it 1/2 open at that point? Or is it closed off?

84porsche9113.2 · 06-19-2007, 11:55 AM

PBH, thanks for the info. No I exactly have not done the testing you posted in detail. However if you read the first note it says if the switch is not functioning properly, the idle will be high at 1,200 rpms. This is not typical of the problems I am experiencing so by the way the car is acting, I do believe my idle switch is working and set properly and it would just be a waste of time for me to go through this procedure.... If I was having high idle problems then I think this procedure would be of benefit.

I too would be curious to know whether the ICV is closed off or half way with the jumpers in place on the test block.

The next thing up the chain from the ICV is the AFM. As I said the ICV is pretty new.

As both you and ned seem to indicate, something seems to be amiss that I am idling so low with the ICV blocked off and the idle screw backed out all the way. I would have to suspect the AFM. If the idle bypass passages are not blocked, the screw is backed out all the way, according to you guys, I should be having higher idle than 250 with the idle screw backed out all the way.

The very fact that I have abnormally low idle with the ICV blocked off to me means at a bare minimum that something other than the ICV is also causing the problem (my hunch is still that the ICV is good). Basically, since I can't even get the car to idle properly without the ICV, then the problem points in the direction of something other than the ICV, I believe.

If I was able to get the car to idle properly without the ICV, then when I put the ICV in the loop things get bad, then it would point to the ICV.

But right now since I can't even get a good idle without the ICV, it must be something else. And it's not the bypass screw or the bypass passages since they were very thorougly cleaned recently.