jon91581

Hey guys,

Thought I might try and get some answers from the collective brain trust. I've done a search on Pelican and here for cars/members that have reported a similar issue, but have not found a remedy to my problem.

Issue: Car starts and idles fine on cold start. I don't seem to have much of an issue backing the car out of the driveway, but within the first 5-10 minutes of driving, the car will stall when decelerating or coming to a stop. The car will immediately startup and drive normally afterwards, so this issue hasn't left me stranded.....yet *knock on wood*. My observation is that it seems to happen if I rapidly let go of the accelerator and push the clutch in as I'm putting the car in neutral at a stop light. If I keep the car in gear and engine brake to let the revs drop to 1,500 or so, and push the clutch in, the engine doesn't stall. This usually only happens once or twice, and then afterwards, the car drives fine. No hesitation in the upper RPM range (i.e. doesn't seem to be a fuel delivery problem) and idles rock steady at 850-880 rpm.

I do notice that right before the engine stalls, as the revs are dropping with the car out of gear, the oil pressure drops.

Here is a quick list of parts/procedures done to try and remedy the problem:
1. Replace/check DME relay - no fault
2. T-OBD scan and idle adaptation - O2 sensor fault, which I cleared and have ordered a replacement
3. ISV replacement with new Bosch part
4. Check idle and WOT switches - no faults

If anyone has had a similar problem and come up with a solution, I'd love to try it out in my situation.

Thanks,
Jon

Steve Weiner-Rennsport Systems

Hi Jon,

Sorry to hear about your stalling issues; looks like you've already done some good troubleshooting.

A few questions if I might:

1) How many miles on the car?

2) Can I assume you have the OEM dual-mass flywheel?

3) Have you checked battery voltages at 2K RPM (must be 13.8-14.2 VDC)

4) How old is your battery?

5) Have you thoroughly cleaned the battery posts & cables at BOTH ends?


The answers will be very helpful for me .

jon91581

Steve, I've included answers to your questions in red.

StopLookGo

Fuel pressure regulator?

Steve Weiner-Rennsport Systems

Thank you!

I'd suggest checking battery voltages at 2K RPM to make sure your alternator is OK as well as checking the date code on the top of the battery. If its 4 years old or more, its VERY suspect.

koenig_roland

i had similar issues some years ago. I changed the battery ground cable - and some weeks later the engine-ground cable "while i was in there" - and the problem was gone...

never happend again. And yes, my "old" ground cable also looked like new... :-)

jon91581

Hey guys,

Just went out to the garage to check voltage on the battery and at 2K RPM, with and without A/C. Here are my readings:

1. Engine off - 13.10V
2. Engine on at idle - 14.30V
3. Engine on at 2K rpm - 14.2V
4. Engine on at 3K rpm - 14.2V
4. Engine on at 2K rpm plus fanspeed "4" and A/C on - 14.13V

Based on these results, it seems the battery and alternator are functioning okay. I'll try cleaning the battery ground cable and battery terminals next. If that doesn't work, I'll probably replace the battery ground cable and order the starter ground cable as suggested by koenig_roland in the post above.

Any other thoughts or suggestions?

Thanks,
Jon

lauris

O2 Sensor may cure this.

One of mine started just randomly stopping but would immediately restart. no real obvious reason why, sometimes when cold, sometimes when hot, sometimes didnt do it at all.

the lambda sensor was seeingly giving wrong signal to ecu which was either over or under fueling the car, causing it to stall. new sensor fitted, and hey presto fine again,

cant be 100% but sounds very similiar - especially as it restarts immediately ok, but there is a slow running sensor that can cause issues when backing of the throttle,

would be interetsed to know what cures it

regards
Scott

jon91581

Thanks for all the insight, guys. I should be getting the O2 sensor this week, will install and report back. Also looking at purchasing a replacement battery ground strap to replace. Will try the O2 replacement first since I already know it's faulty.

Will report back as soon as that's taken care of. Hopefully, Scott is right and that'll cure the issue. Before the O2 sensor error, I didn't notice this behavior, but I'm surprised that the DME wouldn't be able to compensate. Again, I'm nowhere near an expert with the electrical systems of the 964, so I'll just go through systematically replacing/repairing things that I know are wrong/failing/broken.

Jon

jon91581

Quick update: Received the direct replacement Bosch O2 sensor this morning and used Smokin's very helpful DIY (https://rennlist.com/forums/964-1989...placement.html). Replacement went very smoothly with the exception of stripping one of the aluminum lug nuts on the driver's side rear wheel. Also found that my heatshield was missing a 10mm nut, but I guess 3 out of 4 ain't bad.

Put the car back on the ground, and fired her up. Idle was initially a little higher than normal at about 900 rpm. Took the car for a drive, and although the RPMs dropped when coming to a stop light, the car did not stall. I kept driving for a little while longer to get the car up to full operating temperature so I could run an idle adaptation back at the house.

On the 30 minute leisurely drive, I had a couple of instances where I thought the car would stall, but the RPMs only dropped to about 600 before bouncing back up to a stable 850 or so. Is this a normal issue/occurrence? I can't remember whether my car did this before it started stalling. I'm not going to say the problem is cured, yet, but the O2 sensor failure (#24) is gone, and I haven't had the car stall on my short drives.

Still going to change out the battery ground cable and starter ground strap once they get here.

Thanks for all of the help and will update if anything changes!

Jon

greg1990964

Sounds like you are on the right track. All that stuff adds up with a finicky car. Mine stalled when I first got it. Replaced cap rotor, isv and all has been great.

Earlydays

When you say "stripped a lug nut", do you mean the outer corners of the nut? If so, only use a 6 sided socket on the nuts to prevent this.

Jacke2c

964's have many grounds... often in places you wouldn't suspect, like right behind the coil packs. There is another ground on the car up near the starter that is difficult to get to. More often than not, when you have ground issues, you can sometimes have brief or intermittent "Christmas tree" lighting effects. When I bought my car, it stalled much like you describe. My ISV valve was fouled and oily, and the car just had not been maintained. I spent 4-6 hours looking for and cleaning all the ground points that I could find... like the four in the frunk (where the headlight wires enter the frunk, and again up near the bulkhead, followed by a search through the engine bay. They may not be the direct cause, but as an old electrician, faults often occur because random voltage spikes caused by poor grounds can have you chasing problems that don't exist and force you to spend money you needn't.

It is cheap insurance to spend some time with the car and you might be surprised how corroded the grounds are with the "white powder" from the galvanic action occurring between the dissimilar metals. my $.02 Best of luck since I know it is frustrating. Jack

ps. there was an old service bulletin about the AFM valve for pre-91(?) cars and how the connector is supposed to be tie wrapped back to itself where it plugs into the AFM. The problem was very similar to the symptoms you describe if memory serves me correctly.

pcarplayer

Jon, you and I have exactly the same symptoms. Interestingly the idle is quite good around town. Its only after a good drive over distance with a some amount of constant throttle parts (e.g. highway) the idle dips down to +/- 200 rpm when coming to a light. Sometimes it catches and bounces up to 1200 before settling at 850, occasionally it doesn't catch and stalls.

Mine started after the engine got quite wet so I can't help but feel its an electrical or contact issue

I'm very interested to hear how you progress. If I have any updates with mine i'll let you know...

jon91581

Another update: So far, so good. I've been driving the car for the last couple of days, and it seems like the intermittent stalling issue has been nipped in the bud. I'm still changing out the battery ground and starter ground straps, but will probably wait until I'm doing an oil change to get to the starter ground strap replacement. Also going to go ahead and clean as many of the grounds that I can find.

Earlydays - I stripped the threads of the aluminum alloy lug nut while bolting the wheel back up, which could probably be attributable to some tire shop using an impact wrench to put on the lug nuts. Steel lug bolt versus alloy lug nut....steel will win every time!

Turbotwoshoes - Based on my maintenance records that I've got from the previous owners, the service bulletin fix was performed. I haven't touched the AFM during my ownership and in the PPI, didn't mention anything, so I'm assuming that it's still zip tied. If I get some more ignition related issues that I believe are related to the associated interference, I'll take off the airbox and check it out.

Still surprised that my issue seems to have been resolved by the replacement of the O2 sensor. I really thought that the DME would be able to compensate, and I guess in most instances, it was able to. Just every so often, it wasn't quite quick enough and the car stalled. Hope that anyone else that has similar issues finds as easy a remedy as replacing an O2 sensor. ToreB/Rennlist diagnostic cable and software were instrumental in figuring it out.

Thanks,
Jon