90 S-4

This is the original thread >
https://rennlist.com/forums/928-foru...t-problem.html
That problem is fixed, new problem > starts fine cold, doesn't go
to a fast idle, but does idle smooth and drives fine.
As it gets closer to operating temp the idle starts to go down & down
till it gets to about 400 rpm then dies.
It will restart ok but won't have a normal idle speed.

Parts changed >

coils & coil wires
plug wires w/new resister ends
plugs
caps & rotors
oil/filter
air filter
temp 2 sensor
O,2 sensor
MAF
adj fuel pressure reg
8 ford/bosch injectors 24lb set at 36psi
4 rubber fuel lines
Ignition/injection circuit Monitor Relay replaced with > "By Pass Relay"

Things checked for proper operation >

Swapped in another LH computer, didn't change anything
checked the temp 2 connection at the ecu's (ohm checked ok)
fuel dampeners ok, checked with MitiVac ..
fuel press reg replaced, wouldn't hold vac with the MitiVac test
fuel pressure remains constant !
checked for general vacuum leaks, none ..
sorta checked for good grounds, everything seemed ok ?

Any ideas where I can go from here ?
Thanks,

ammonman

Is your Throttle Position Switch working and properly adjusted?

Just a thought.

Mike

90 S-4

I forgot to mention that , YES it is
thanks..

blown 87

Do a intake service on it, replace everything including the ends of the wiring harness, TPS, IAC, Knock sensors, all the hoses.
Do replace all the harness ends, even if they look great, including the MAF end.

with every thing else you have done I would be surprised if a intake service does not take care of your problem, and have you had this sharktuned for the bigger injectors?

90 S-4

Blown 87
Absolutely was planning to get it shark tuned (see orig thread)
I had wanted to get high flow cats and Rogers new EIS then
Sharktune it for all the mods but I can't go anywhere now until
this current problem is solved.
I feel like I've already thrown the kitchen sink at it, with the
additional work you just suggested I don't think I can bring
myself to do that just yet.
I thought the description of my problem was clear enough and
simple enough that someone else must have experienced
it also and they could tell me which part to change.
I can't believe this is the only 928 in existence to have experienced
this symptom. (gets warm and dies, jeeez) I can see why people
get frustrated and put Chevy's in these frickin things
The only thing I can think of at this point, and its a wild *** guess
is that it needs to be Sharktuned for the 24lb'ers so it will idle.
If that is true then please someone with experience tell me so, so
I can go ahead and do the cats and EIS then have to only make one
expensive trip to the Sharktuner instead of two ..

blown 87

You will need to get it in tune before you install new cats or risk damaging them.

Yes, other 928's have had that issue, and others similar to what you have.

Does doing a relearn on it help until it relearns?

As far as doing a intake refresh on it, has it ever been done?
If not, we both know what the hoses (and parts of hoses) are going to look like.

To me it sounds like you have a IAC problem, to get to it you are going to have to pull the intake off, no way around it.

Mine had a couple of issues after I did the intake and hoses, I had tried to save some bucks my buying non Porsche TPS and IAC when I did mine, I did not do the harness ends, want to guess how much better it ran when I installed OE parts and new harness ends, which looked great BTW.

sounds like you have covered most of the other things and you know that you need to pull the intake, but you are trying to convince yourself it is not so, been there man.

One thing i do know with out a doubt, the rubber in the hoses under the intake are not up to the task, they will turn to gummy soft crap in a hurry ones oil gets to them.

90 S-4

I'll try the re-learn and see what happens, thanks for the advice,
I'll report back later..

Stromius

Joe, Have a close look at the Temp2 harness/plug and the same for the MAF. Mine were wrotten/bare and likely touching at times giving me issues. How about the CPS connector under the throttle wheel (under airbox) - there was a thread back a ways about connection issues at the CPS that were temp related. (Mongo?) Is the CPS/CPS connector in good shape or goner? Visible cracking is a bad sign but typical of age. Good luck!

90 S-4

Stromius,
I think the MAF & temp 2 are ok but I'll check the CPS -- Thanks

Stromius

Sure thing. I did mean the wiring in the plugs/rubber boots of the MAF and Temp2.

Mongo

I had similar symptoms on mine and I had a loose LH ground and a messed up MAF connector.

Those are some great areas to check out.

On a side note, if yours is an auto, consider checking the flexplate movement by releasing the pinch collar and doing a crankshaft endplay check too.

Bill Ball

Still fussing with this? I know you checked temp II both hot and cold and that the idle stabilizer was plugged in, but did you check temp II when the motor is acting up? I would check it at the sensor, then go back and disconnect the battery and pull the LH and EZK plugs and check the value there again. I wonder if the idle stabilzer is having a heat-related failure, but I'm not sure how you could determine that. The Hammer/Spanner/Theo Diagnostics tools will cycle the stabilizer. A diagnostic test with any of these tools might show a helpful error code. I see you swapped LHs without a change. Kinda running out of things to check. You believe the grounds are OK, but have you checked the ones on each end of the throttle wheel plate under the MAF area, like Mongo (Andy) mentions?

Rob Edwards

Joe-

I'm a moron with a capital M - I should have handed you my Spanner when you were over, dunno why I didn't think to give it to you. I will be in Laguna Hills tonight from 6-8:30. PM me your home address in the next 2 hrs and I'll drop it off on your porch.

jon928se

I don't want to post this really but have you checked the crankshaft end float. The symptoms you describe are precisely those of failing/failed thrust bearing. - Idle and start fine when cold, doesn't want to start or turn over idle speed consistently low when hot.

Fingers crossed I am wrong.

Bill Ball

Jon: He said earlier it turns over rapidly even when hot, but maybe this bears repeating. It came up in the earlier thread, and we seemed to rule it out BUT slow idle and dieing when hot sure fits TBF. Maybe the fact that it still turns over well when hot and now starts OK, (just idles slow) is leading us away from TBF when it shouldn't. Endfloat should be checked on all later ATs regardless. I don't think he has done that.