I have a 1990 S4 with the following symptoms on a hot day.

Initial start in the morning after sitting all night with A/C on at start; it's 70 degrees ambient: Starts right up, no problem. Runs fine all the way in to work no issues. No stalling at stop lights, etc.

Car sits for 45 min-1 hour after drive in to work (20 miles), 80degrees ambient, A/C on, water temp at about 115: Cranks fine, engine fires, RPMs spins up then quits. You can do this 2, 3 or 4 times; same thing. Hold down the gas pedal just a bit, starts right up but doesn't want to spin up RPMs for a second or so then runs. If you don't "play with the pedal" a bit she will stall out again at start.

Last start of the day-going home; 93degrees ambient: Start sequence is same as 1 hour of being parked. Car drives and runs fine on freeway. A/C is good, nice and cool... Water temp at 175 as indicated on gauge. When coming to a stop from the exit ramp she wants to stall out at idle. "Play with the pedal" and she will continue to run. She runs fine on the side roads above idle. Wants to stall out at stops.

Any clues?

Thanks,
D

 

A couple of things to check...

Pull the vacuum lines from the two fuel pressure dampeners and the fuel pressure regulator and check for any trace of fuel in the lines. If there is any trace of fuel in the line, replace the leaking unit.

Check the resistance on both Temp II sensors. The sensors are in a common housing on the top front of the engine - one pin for each sensor. Check from each pin to a good engine ground, never from pin-to-pin. At room temp, there should be 1.4 KOhms to 3.6 KOhms; at 104 deg F, 0.9 KOhms to 1.3 KOhms; at 175 deg F, there should be 250 - 390 Ohms.

 

Thanks Wally, I'll take a look at this tonight.
D

 

Well, I pulled the vacuum lines and there was no sign of leakage. The temp sensors were fine across from ambient to 175 degrees.
Today as I was pulling to a stop the engine just quit like I had turned off the ignition. It cranked back up with a little pedal and ran fine the rest of the trip.
The saga continues...

 

Age of your LH brain, and your last crank end play measurement? (Apologies if this is posted elsewhere!)

 

Check your ground strap or your + battery terminal. Somtimes they give wierd problems when they have additional resistance.

 

I have the same symptoms with my 91 S4. Its in the shop now, Munks Motors Waterford MI.
Their initial thoughts were the same as Wally's.
When I hear from them, I'll let you know what they find.

 

End play is fine, I've always kept an eye on that. The ground terminals have been cleaned routinely.

Rob I'll be very curious about the result when you get it. Also, the cargo carpet came in today; I should have never seen a piece of new Cashmere Silverknit. LOL! I thought my old stuff looked pretty good yesterday.
I'll be getting the rest of the carpet sometime later this year or early next...
D

 

Munks tells me they couldn't duplicate the issue.

I'm back to square one.

 

There are times that it runs as it should. Others, it does the drop dead stop or the 300-500 rpm idle where you have to play with the pedal to keep it running. It does both during the hot months of the year rather than the spring/fall times.

 

I wrestled with a similar issue. I found the following Inspecting a 928? Link: 928 Periodic Inspection.pd

My temp II sensor was bad, but it was a good exercise to confirm that all other checks found nothing busted. What also helped was spraying 3/4 of a can of WD-40 in an intake hose(search for procedure) to lube up the ISV.

Larry

 

I think the symptoms on mine are slightly different.
It always starts easy. It hesitates and stalls only when restarted after sitting for 5 minutes to about 2 hours.
If I feather the throttle and hold it at about 2K for 30-90 seconds, it clears up and runs fine from then on.
The symptom is almost like vapor lock.

 

I replaced the fuel filter, temp sensor II and pig tail, O2 sensor, and several relays. All the easy stuff.

 

Rob,

I had the exact same symptoms on mine and it was a leaking fuel pressure reg. and damper.
Change both - actualy both dampers and the reg. - and everyhting's fine now.

 

Check valve on the end of the fuel pump will give symptoms as you describe. Cheap and easy to replace.