nord

Hi!
Need some help from you guys..
I suddenley started having trouble with my 1988mod s4 32v engine.
Changed the timing belt last week but the car has been running good until now.

The symptoms are:

*Very rough idle..from 300-2000 rpm.
*Harder to start when hot.
*The spark plugs are all black.
*Erratic engine when driving in low speed.
*Think it's running rich.
*Getting worse every time i try to drive it.
*Lower power output.

Changed idle stabillizer,vakkum elbows,hoses,floppy valve vaakum unit,knock sensors,injector seal's and gaskets yesterday beacuse i had them avalible but with no differense on the engine's running performance.

disconnected MAF yesterday and it idle'd smother but very low...also checked to see if the burn off sequnse was working...but couldent see anything glowing down in the MAF.

Any ideas what the problem could be?

Ron.

Daniel Dudley

Check your timing, first and foremost. I overadvanced a timing belt a few years ago and toasted the cats. I don't think that is your problem, but since you just changed the TB, check the timing and eliminate that as a variable. Also, check your temp sensor connection.

69gaugeman

Maybe TBF? Is this an auto? Check pressure plate and crank endplay.

SwayBar

Running rich, black plugs, and then doing this:
I vote for MAF. See if you can borrow a used one and check how the car runs with it installed. If it still runs poor, then it's the LH.

Mike Frye

Ron,

<NEWBIE QUESTIONS>
I have no experience with the s4, but for clarification, you said you did the TB last week, and it's been running good until now. How many times have you started it since then, how many times driven and how many miles? Anything else done at the same time as the TB, like the WP? Cam gears? What else was out?

I'm sure these other guys have a handle on it, but from a troubleshooting standpoint, some other experts might respond if something rings a bell with more info.

I'm just watching and learning because I can ask questions with the best of 'em.

nord

Hi everyone!
Been out in the garage now working on the car..
It seem's like the burn of sequense in the MAF is working fine.

I've been driving it every day for a week so i dont think it's got anything to do with the timing belt change.

Tried to disconnect the temp II and it runs alot better and idel's much better...no problem driving it but far from perfect.

Could it be as simple as the temp II..?,anyone that now's how many Ohm it will measure on cold/hot engine?

Ron.

Giovanni

*Very rough idle..from 300-2000 rpm.
*Harder to start when hot.
*Erratic engine when driving in low speed.
*Getting worse every time i try to drive it.
*Lower power output.

If its an automatic I would check for TBF first!!!! https://rennlist.com/forums/928-forum/260921-thrust-bearing-check.html and if it checks out fine than worry about the LH and/or MAF.

Scott M.

Does it feel like it's running on 4 cylinders?
-check for a loose coil wire or bad coil.

killav

If you can't get your hands on a MAF, John Speake has an excellent write up on website on how to at least partially check your MAF for gross failure.

http://www.jdsporsche.com/faqs/new%20MAF%20FAQ.pdf
Scroll down to "I can't borrow a MAF, what else can I do?"

Make sure all of the rubber hoses are connected properly to your MAF boot. I had one that popped off (idle stabilizer hose) and my car would not run on its own unless I un-plugged the MAF, which then put it into limp home mode.

TBF is always a possibility in an auto. When is the last time you have checked this?

There is also a test for the TEMP II sensor. All it takes is an Ohm meter. Maybe somebody could snipe the sheet out of the shop manuals?

michaelathome

This sounds EXACTLY how my car was when I got it, turns out my O2 sensor was unplugged forcing the car to run on the WOT map. Yours may have failed. Only difference here is that mine wasn't getting worse, it was always the same. At a stop light/sign w/the brakes on it felt as though it would stall then idle up to 1200 and back to 3-400 again. Blackened plugs and slight smoke out of exhaust when under heavy throttle.

Good luck,

Michael

Mongo

How can you factor in a thrust bearing failure if he's running massively rich and idling erratically? This is a fuel injection issue, not a mechanical failure. If you have a thrust bearing failure, the engine would have massive chattering, knocking, or would even seize upon startup most likely.

It has to be a sensor issue. A new Temp II sensor may help if you said the running improved when it was disconnected. If it still runs rich, ever thought of a fuel pressure regulator failing? When they do, sometimes the car runs FULL RICH.

O2 sensor is another good idea. The trouble is with FI cars, it could be a number of things that could lead to poor running. Start with the simple stuff first. It helps.

Jim bailey - 928 International

while the first point is correct This is WRONG ..."If you have a thrust bearing failure, the engine would have massive chattering, knocking, or would even seize upon startup most likely." There is NO NOISE, NO CHATTER, NO ROUGH RUNNING, at all and yes near the end the engine stalls at idle, may not crank when hot on the starter motor and the oil gets filled with powdered aluminum. But this "engine problem" is most likely a fueling issue.

Shark Attack

expand on hard to start when hot... will not start or slow crank?
I agree with jim, i think one of your sensors went bad and its messing with your fuel mixture

Mongo

Woops. False info Jim, would the aluminum shavings show up on the dipstick in the event of a TBF? I'm kinda tired of hearing everything blamed on TBF, which is not very common on 928s, and rarely happens, but yet scares the majority of people on this forum. I mean c'mon, it's like the equivalent to having Eddie Griffen autocross your car

killav

So, in quick summary,

MAF
Temp II
O2 Sensor
Ruptured fuel damper
Possible False Air (vacume leak) causing rich/lean mixture conditions. This one is out there a little, but possible.