928S4 accelerates then dies when stopped

[karlsplace]

My 1990 928S4 with 150,000 babied miles has an issue. When accelerating and then coming off the gas, the engine drops below 400 rpms and then dies. This seems to happen when the engine is at operating temps more often than when cold. I have been riding the gas pedal when stopped to compensate, but, I suspect that this is not good on the torque converter.
My beloved beast is the best of the best and cruising the long stretches of road in Georgia is great. Computer says 22 mpg at an average of 78 mph, not bad for a heavy 19 year old automobile.

[Mrmerlin]

Has the intake ever been refreshed?
What was the last thing you fixed?
You should test the TPS =throttle position switch.
See if you can hear it click when the throttle is opened , you will have to do this under the hood and use the throttle quadrant to operate the cable to the throttle.
If you dont hear a click when the throttle is just opened then investigate if the throttle quadrant to throttle body cable is too tight. ( the cable may not be returning to its stop) thus keeping the fuel shut off
If its clicking I would test the cabling at the computer to see if the electrical portion is working

[Eturbo924]

My 1987 does the same thing.

When it first happened I found the MAF boot was loose and popped off. Reconnecting it and seating everything made all well for some time.

Now it is doing it again and I figured it was the same thing... but alas it was not.

I do know my top end has not been refreshed in some time. karlsplace what parts would be suggested to replace... if on a budget.

Also I know my ignition wires are not in the best shape. I found a destroyed drivers side coil wire and had to create one from wires I had. So those are now on order.

I also recall I checked to hear the TPS switch last time around. I had thought that might be an issue as well since it did the same kind of thing my 1988 Ford Bronco did years ago. Had thought about that last night when the 928 died last night coming home from a cruise night. Not a good showing in front of all the new corvetts. Dou!

[karlsplace]

I will try all suggested. Currently, the ultimate of cruisers is in the Atlanta area being attended to by one of the best and this issue has defeated him for years. the last part replaced was the alternator harness. damn wiring burnt to a crisp. the last part prior to that was the light for the hatch and the hatch release switch. all were easy repairs exclusive of the alternator harness, at $1000, that one was not easy.
Any other suggestions out there??
karl

btw - I will update this thread once I hear back from the mechanic/owner of European Classics, Atlanta, Doc Howard.

[Danglerb]

TPS and ISV would be what I check.

[928Guy]

No one has mentioned it, but if you're shark is an auto, TBF is a real possibility with your symptoms. If you havn't done it yet, pull the flexplate cover and relieve the tension on the flexplate. While you are down there, check the axial play. If it's more than .015" you are out of spec, and probably eating youer block with your crank. Here's hoping it just something electrical, vacuum, or F/A related....

You should add your car details to your signature for future help.

[Eturbo924]

Does the car make any particular noises if the thrust bearing is toast?
Soon after purchasing my 928S4 auto I released the tension on the flexplate... not that I saw any deformation of it... but I went through the exercise anyway. I did not check the play.

Anyway... my car has a pronounced whine when starting up and shutting down. Like a supercharger spooling up and down.

Just as an update on my car. I checked for the TPS switch click and mine is clicking. How do you do this? "If its clicking I would test the cabling at the computer to see if the electrical portion is working"

[Danglerb]

Voltage or continuity at the brain end of the engine harness.

ISV I'm not sure how to test, maybe by replacing since they always go bad eventually.

[paintballer317]

it could also be your oil. my 83 just started doing the same thing and the warning light would flash. i checked the owners manual and it says to check your oil level. low and behold, it didnt even reach the dipstick. : O so i added oil to put it back into the normal range, and it ran so much better after that. it did start to do it again and when i looked, the oil was all over the outside and bottom of the oil pan, so i think i have a leak somewhere. : / but i would have to hold the gas down a little bit and keep the idle up or else my oil pressure would drop and it would die on me.

[karlsplace]

Guys,
The problem seemed to have been the air flow meter located between the injectors and the air cleaner. It seemed that when the motor shut down the wire did not clean itself and kept the the debris from being burned off - self cleaning. That is the explanation that I received.
My beast runs like a 2 ton skinned cat. Just finished a trip from Atlanta to Wartburg, TN and onto Charleston, SC. Coming through the mountains between Knoxville and Asheville was tons of fun and would do it again anytime. Lots of others tried but FAILED to keep up. Good thing a turbo 944 was nowhere near me. The internal computer (is it accurate?) claimed an average speed of 73 and an overall of 22.1 MPG.
BTW - the plastic meter that is about 3 inches by 1.5 inches and located in the space between the block and the intake manifold (probably wrong name) and controls the idle and shut down procedure went bad while at the shop. The Hammer - said so and anything manufactured by Dr Porsche, can't be all wrong
Again, guys thanks for all your suggestions. The shop that found the problem was European Classics in Atlanta, 770-409-9246 - talk to Howard, owner and mechanic par excellence'.
karl

[MPDano]

Originally Posted by karlsplace

my beast runs like a 2 ton skinned cat.

That is a hilarious statement!!

[karlsplace]

MPDano,
I just could not spell scalded.
I had a few other phrases to select, skinned cat sound the weirdest.
karl

[Mrmerlin]

so the throttle position sensor was bad?? TPS??

[karlsplace]

Nope the Air Mass Flow sensor. Does that make sense? Is that the same as the TPS?

[Mrmerlin]

MAF= mass airflow sensor
TPS= throttle position switch