Tom. M

Took it out for a little drive around town. Again while warming up the idle was a bit up and down. But after fully warmed, it ran smooth as glass and the idle was rock steady and around 600 to 700...smoooooth.

Lizard928

Has the intake refresh been done on this car?

Your latest symptoms sound like a vacuum leak in there.

Tom. M

It was done back around 03... funny about the idle thing...was that it was smooth..as if pre-programmed. Have you ever seen the idle adaptation when connected to the Bosch Hammer?... that is what it was like. I'll run with the new brain for a week or so and then swap in the old one to see if the missing/roughness returns..

blown 87

Idle issues on a 928 can be frustrating, and really frustrating when they only happen once in a while, after everything that is normally done to cure a idle issue has been done, and done again, suspect the LH.

I had two LH units that were known good units that has just sat for a couple of years go bad with a sudden, and intermitiant loss of idle control and surge.

That being said, you still need to check the other know issues that can cause this problem, vacuum leaks, harness ends, TPS, IAC, 02 sensor, grounds, every thing else before you condemn a LH.

fonetico

I've posted on this on several occasions in the past. My '90 S4 has demonstrated all the same symptoms for two years and the problem's particularly chronic in winter weather. Interestingly, if I start the car without touching the accelerator, it idles fine. As soon as the pedal is depressed the idle goes wild.
In response to the expert advice on this forum I've tested and replaced the usual suspects, to no avail. In fact, it's getting progressively worse.
Why does it only happen when the car's cold? What bits are sensitive to cold temperatures? I've checked and replaced the Temp II sensor twice with no discernible improvement. The MAF was replaced recently and there appear to be no vacuum leaks. The throttle mechanism seems well lubricated and working as expected.
The only things I haven't tested are the idle switch and the ISV. Didn't know how to without taking them apart, which would be beyond my capabilities.
Then I saw a posting from WallyP on a simple test for the idle switch. Drive the car at speed, set the dash to Instant MPG and take foot off accelerator pedal. The dash should read 90 mpg.
Mine fluctuated between 9 and 21! When the car warmed up and the idle steadied the dash read 90.
Evidently, when the switch was warm it closed normally. Once opened when cold it would fail to close until up to working temperature.
All this, however, remains as speculation until the weekend. That's when I'll collected the car from the workshop with a new idle switch and a new ISV as, I'm informed, it's worth changing both at the same time. This isn't going to be cheap but these are the actions of a desperate man.
I don't know whether this contribution of mine will be of any use to anyone but this idle problem seems to be such a frequently recurring phenomenon.
I've yet to learn whether my problem has been fixed and perhaps this posting is a little premature. I'll update over the weekend. But I have appreciated hearing from others about their tortured journey to solving problems.

Tom. M

Mine is a Cdn spec 928 so I've got liters/100km as a gauge. It does respond..goes down to near 0 l/100km...but doesn't show --- until I'm nearly stopped. I replaced the WOT switch back in 04 or 05 ish when I did the valves. I do hear the click when moving the throttle too..so likely not an issue on mine..but good point to check .. thanks

fonetico

For what it's worth, I could hear a healthy click when moving the throttle too!
I've just collected the car from the workshop and the trip home has been the most blissfully smooth and throttle-responsive ever. I need to wait for a cold morning start to see whether the wild idle has been cured completely though.
Fingers crossed!!!

Tom. M

Update 4/30...
Drove the GT up to a local event today (exotics at redmond town center..click here for pics.. Enzo included http://s252.photobucket.com/albums/h...0April%202011/ )...

It did fine with other brain on the way up but still had some odd idle/stumbles. On the way back home, it went to about 4000 rpm and stayed there. I was able to get home but even after shutting it down it and restarting it would stay up there. Finally it came down after sitting at home for a bit. Made sure all the linkages/cables were working and made sure the MAF was properly seated etc. No rhyme or reason as to why it goes up to hi rpm...

What controls the rpm? Is that only the LH? Odd that both brains do the exact same thing. Is there any other input into the rpm control?

Lizard928

The RPM/idle valve is controlled by the LH, yes.

When you did the intake refresh, did you replace the ISV hose? I have seen a number of people replace that hose, and it has split, causing these same symptoms you are seeing here. Maybe you should just pop off the intake and inspect it. Its only a few hours work....

SeanR

When my ISV hose split, I was having hard start, low idle issues (and lean at higher rpm)

I'm still stumped on this one.

Tom. M

well...the high idle stuck thing just ended up being the pedal to throttle (side of intake) cable housing coming out of it's receiver and staying there.. This has happened before on the firewall side..so I wasn't looking for it at the intake..

I went out to disconnect the maf and it ran crappy as before..but then I put the cable back to its original spot and it ran better... but not perfect.. still some weird idle blips...

SeanR

If the cable is pooched, this would account for a great many of the issues.

Tom. M

Im probably going to take it out to the PCA event tomorrow...just to see how it runs. The cable was replaced 4 years ago at Sharktoberfest (it was frayed big time).. but will make sure it'll stay put this next time to see how the idle issues are coming along..

Tom. M

Just went out to take the GT out for some gas... it started to go back to the same old idle issues..so I pulled out the phone and took some video. Ignore the voltmeter (and the three whacks on the side of the pod LOL)... but as you can see in the video...idle is all over the place and went up to 2K and stayed there after I stopped the video... This is just weird..has a mind of it own..

http://s252.photobucket.com/albums/h...idleissues.mp4

killav

Tom,

I think John C. (soontobered) had his 89 doing some real funky stuff and all it ended up being was a ground issue (I think it was one of the main engine grounds). PM him if he doesn't catch this thread.