chris walrod

Pull the dizzy caps and have a look for carbon tracking. At a minimum, clean the insides of the caps. I doubt its your problem, but worth a look.

midnite993

I have not tested the TPS or MAF yet...will do so after the fuel filter job. I also ordered new caps and rotors which the car also needs anyway.

Thanks for the advice so far...wish me luck! The Sierras are calling me...anyone drive highway 190 before? I'd hate to have to drive this road in my wife's ratty old '97 Civic:

http://www.mighty190.com/

geolab

To me it looks like it is a fuel problem. You said the fuel pump was changed at the dealer, problem number 1.
When installing a new fuel pump, a new retaining valve should be installed. It is a small valve which is located
between the pump and the fuel out hose. The majority of the dealers do not change the valve. If you buy the pump from Bosch, the valve is included,
from Porsche, not. I have a new one I can send you if need be (free)
Then the fuel regulator might be the culprit.
New pump but no new filter? curious. AT THE DEALER????? convinces me more 'bout the retaining pressure valve.
Start with changing the filter, and then the fuel regulator on top of injector 3.
The retaining valve needs removing the pump out again.

David in LA

Hmmm....a MY95...has the wiring harness been replaced under recall? My euro-spec MY94 993 had stumbling, surging, backfiring and startup issues. Harness was totally fried when they pulled it out.

fnckr

+1 here for the cat being clogged. Mine was just replaced due to stalling and not revving past 5400 rpm.

chris walrod

This may help his long starting problem but might not help the stumbling troubles.

I didnt realize the valve was included with the pump as sourced from Bosch. Good to know!! Thanks Geolab!

CP

Did not read every post here, but try the MAFs. That's the classic symptom when the MAFs failed in my M5. Good luck.

CP

1pcarnut

Does the car have a K&N by any chance? If so your MAF may be toast. Either way, at least try a good dose of CRC MAF spray on it, couldn't hurt.

geolab

That is exactly why I have a new one. I bought it from the dealer @ 40 euros before
my Bosch pump arrived. When I received the bosch pump it had the valved installed already.

TheOtherEric

Definitely test the fuel pressure and fuel flow rate. Both procedures are described in the shop manuals.

I'm betting a cat issue, though.

geolab

What eliminates the cat for me is :
1- it revs on neutral to redline, (same amount of exhaust airflow under/without load)
2- it is worse when cold
And worse when cold could be fuel pressure, with pressure build up later when hot, midnite says it turns from the first try.
I hope we find the culprit soon

fnckr

Actually geolab think about this. It's tough to apply full throttle exactly at redline while in neutral. The engine would blow right past redline violently. You can apply throttle gradually to get to redline or you can floor it well before redline, but cannot maintain it there.

However, under load, as in my car, I couldn't get it past 5500 rpm even with full throttle application. Actually at 5500 rpm it would still accelerate but in barely noticeable increments even with full throttle.

Also, when cold, the engine has to fight more friction due to thicker oil, less fuel flow, etc. which would make it even more difficult to get to redline. I say do the pressure test on the cat, or just remove it.

midnite993

Well, did the cat pressure test (no increase) and the fuel flow test, and everything seems to be working fine. It filled my 1 quart container in about 30 seconds. Is there such a thing as too much fuel pressure? Would that check valve described above (that gets left out at the dealer) cause this?

Next I will try to clean the MAF sensor. Do I need to remove the sensor to clean it, or can I just spray the cleaner through the MAF intake behind the air filter?

The car had a K&N filter on it which I recently replaced with a stock paper filter, in fact just before this problem occured. Thinking this might have caused the problem, I ran the car again with the K&N and the car ran with the same problem.

Will let you know about the MAF...

chris walrod

Remove the MAF -- its not too hard to do -- you'll need to loosen a hose clamp way back behind the ISV valve to get the MAF tube free from the intake. This is after the airbox is removed.

VNTGSPD

Going back to the simple things...

Did the problem occur immediately after the air filter change? If so, I would do two things:

1. Remove the filter and drive the car to see if the problem persists. I have read of filters "collapsing" under vacuum pressure from the intake manifold. I think this was mostly limited to aftermarket airboxes without sufficient clamping force to hold the filter in place. This would potentially cause the stumbling/loss of power.

2. Check all hoses/wiring going to the MAF and surrounding area to ensure something wasn't bumped or pulled loose during the filter install. If the car ran well after the change and then developed the problem shortly after, this could still be the problem.