rmr25

My '88 S4 auto has developed a rough idle condition: cold starts ok at about 1000 rpm; as engine warms revs drop slowly to around 3-400 rpms and then starts to wander/hunt, sometimes stalling. I've read most of the ISV treatment threads, indicating how to soak/clean the ISV. They all say: go to the plastic "y" fitting just left of the driver side manifold, disconnect the hose going under the manifold and squirt WD-40 or other solvent in there, run, squirt, soak overnight, etc, etc. Here's my problem: that barb-ended hose under the manifold goes directly to a hole in the rubber bellows mounting the MAF to the throttle body. This hole is outward of the throttle plate, so I don't see how solvent can pass it to get to the ISV. Am I missing something? ( I have the WSM fuel path diagram on p 24-214 .)
Incidentally, the PO replaced the ISV at 60,000 miles. Car now has 73,000.

whitefox

Perhaps you have a vacuum leak, I dont think the ISV would fail after only 13k miles, my S4 has the original ISV at 124k miles, although all the intake rubber crumbled apart in my hands.

khalloudy

I think your problem is either Vacuum or most probably MAF failure. I had similar symptoms a couple of years ago and it was MAF.

Sincerely,

RyanPerrella

does your hunting idle symptoms go away completely after about 10 minutes?

I have a similiar thing with my car where i need to hold the gas pedal for the first few seconds or the car will fire then die. Once i get going for the first 10 minutes or so when i get to a light the idle will stumble to 400 or less and sometimes stall as the revs cant maintain the engine idling and it just dies.

I am curious if these symptoms are in line with MAF problems?

Whats the best way to check this to verify thats the problem before shipping it out to be rebuilt?

David L. Lutz

Try this! Take off your MAF to access your throttle body. There is an opening (hose) on the passenger side of your throttle body that goes to your ISV. Insert a small plastic tube (about 12 inches) into that opening toward the front of the motor. Make sure it goes to the front of the motor, because that connector "Y's". Then squirt the WD 40 into that tube and it will spray directly into your ISV.

Good luck!

Bill Ball

You are right that that hose enters the boot below the MAF, but it is also connected to the ISV. You can try the WD-40 squirt into the hose or do it the way David mentions.

SeanR

Are you running an oily K&N filter? When Rog100 and crew 1st saw my '88, they had me take that out due to the fact the oil in the K&N screws with the MAF and causes premature failure.

/hope that is not the case.

Rich9928p

Bad idle speed regulation also can be caused by a failing LH. Check out all the other things and if they don't correct your problem plug a known good LH into your LH connector. If your problem disappears, you know that is your problem.

rmr25

Guys: Thanks for your several suggestions. I don't think my problem is a bad MAF, since I put a John Speakes refurbished unitin just a few months ago. I've gone over all the likely vacuum leak places and don't find anything. If the WD-40 treatment doesn't fix things, I guess I'll be looking at the LH module. Not quite what I wanted!

Andre Roodnat

Maybe this makes it a bit more clear; http://www.porscheclub928.nl/Geschie...Tech/index.htm
The ISV is marked "B" in the centre of the engine. The WD40 tip is worth a try. Mine would also drop to 400 rpm at sometimes or started to surge from 800 upto 2500 rpm all of a sudden. It stalled every time after revving andletting it get back to idle, as the ISV did't pick up. The WD40 did the trick. That was about 4 years ago. I didn't have to replace the ISV since. When the WD40 worked, I also used some sewing machine oil. (very thin oil), as this has a more lasting lubricating effect than WD40.
Good luck.

Waynegs3

Hi Fellas, new to this site, but I am now the proud owner, as of Sat of a 93 GTS. I have a siimilar problem on idle that was drop below 400rpms then die.... hot or cold, with ac or without. I tried the WD40 trick last night and no luck. Actually I did it twice last night just to make sure I did it as people had suggested. I squirted a generous amount into a long hose, like on the wd40 cans, about 14". Till is ran out into the TB. I reassembled and car never smoked, like some of the pictures sugested it would. So possible my ISV is frozen shut? Also, in an effort to keep the car from stalling, i did adjust the throttle cable (to put some tension on it, so car would die) on the cable that is next to the foot cable that runs behind the drivers front wheel. i did check to see where that went and it goes to a VDO box. So with the tension on that, the car did idel correctly, but alas the check engine light came on. So I put it all back to original and light went off but the flame out problem exists... im guessing the ISV is the culprit? Do i have to pull the manifold off to get to it?
Also my boot below the MAF has 2 "Y"'s. driver and passneger sides, I used the passenger side, should i have squirted the wd40 in the driver side instead?
Wayne

auzivision

Y on passenger side feeds the oil/crank/cam breather system.

Y (#8) on drivers side goes to ISV (#2) via hose #11:



Welcome aboard Wayne... now post some pictures of that GTS!

dcrasta

If you remove the Airpump you have to plug a vacuum line from it.

Waynegs3

Ahhh, wow that picture makes perfect now!!!! Where can I get diagrams like that?
Ill give that a try tonight.
Also, I ended up getting 4 928's from an estate sale in CAL. 1 was my GTS and the other 3 were S4's. 87, 88, 90. They were all running except the 88 (times belts were in the process of rebuild). The 90 is sweet, every option known to man! My GTS has 100k miles and so far so good. Thanks for the diagram.
Id post some pics in a new thread.
Wayne

John Speake

Things that can stop car idliing...

Closed throttle switch not closing due to overtight throttle cable. (listen for reliable click when opening and closing throttle)
Closed throttle switch faulty
ISV faulty or stuck.
Vaccum leaks (usually high idle speed) Check vac at idle on the from fuel damper, should be about 21in HG (sea level)
Faulty LH ECU whci controls the idle speed with a closed loop system.

Probably some other points I have missed but these are the main ones.