Stevie

8/2/16- After dinner, the wife and I decided to go on I leisurely drive to the harbor when I noticed a slight hesitation upon startup. Going over bumpy Old Country Rd felt some stumbling with the engine. At a stoplight, the RPMs went south and almost stalled when taking off. One mile later got yellow "PSM Disabled OK to Drive". One more mile later got yellow "Auto Start/Stop Disabled OK to Drive". Then got yellow "Fault Engine Control OK to Drive" but the engine stumbled. Pulled off, shut down, restart saw all 3 messages again. On the way back home got barely enough power to get up the hill. I locked and unlocked the doors 3 times, power cycled battery and restarted no bad engine noise and only one message, "Fault Engine Control".

8/4/16- The car drove fine on my way to the indie porsche shop and they discovered the following codes: DME: P0172 B1 RICH, P301 MISFIRE 1, P0302 MISFIIRE 2,PO303 MISFIRE 3, P0300 TOTAL, 00418 PSM CONTROL UNIT. PDK: P199A IMPLAUSIBLE ENGINE TORQUE. PDK SELECTOR: 1802 SHIFT POSITION GATEWAY, 000401 CURRNT DISTRIBUTOR TERMINAL 30 RESET INSTRUTMENT: 00A008 PSM FAILURE. FRONT: 881202 KEY BATTERY FLAT. Nothing indicated a specific mechanical or sensor/system malfunction. They reset and cleared all codes, messages, tested alternator was charging at 14.2V. The car drove normally. Diagnosis: Sitting in the garage for 2 weeks brought the 4 year old battery to the threshold of acceptable voltage causing the sub-control computers to trip off the Fault Engine message.

8/5/16- I replaced the battery with a new Bosch Platinum and the test drive drove fine.

8/6/16- Drove 2.5 hours to Limerock for DE with PCA CVR running like a champ. At the track, it drove fine all morning. Then, after the 2nd session, driving in the paddock, the engine didn't idle properly and showed the same messages as on 8/2/16.

Spencer *** (great guy) of Speedsport in Danbury, CT, read the codes that matched the ones reported on 8/4/16 and concurred there were no causes listed for the errors. He cleared the messages and the car ran fine in the 3rd session but stumbled during return to the paddock and showed the same messages. I ran the 4th session without removing the messages and the car ran fine until the road back to the paddock when it stumbled again at low RPMs. Hoping I can stumble my way home by keeping the RPMs up, I filled the now empty tank with Shell 93. To my amazement, and the car ran perfectly fine at low RPMs all the way home.

Since then I’ve driven it perfectly fine for the past 4 days with no issue or messages (the ones that appeared at the track must have cycled out). Could I have had water in the gas the week before the DE that caused the misfires only at low speeds? Could it have needed two tanks to clear itself? Have any 991 owners had a similar experience or thoughts as to what might be going on here.

Thanks for your thoughts_Steve

roadrat

No idea. Is your car named Christine?

Jay-S

I've had my car stumble, stall (PDK so not clutch related) and throw faults a couple of times in a short period. Tank of gas I was on was from a different place than normal.

Nothing wrong when I took it in but with a new tank of gas at my normal place I haven't had the same issue since.

I hope it is something as simple as that.

siitech

I had a similar engine stumple, was barely able to drive uphill to reach the dealer. Although the error message I got was "Reduced engine performance Possible to drive on" which was different from yours. The dealer replaced the high pressure fuel pump and has been fine since.

Stevie

Thanks, siitech. Did the dealer advise you of the error codes that prompted the fuel pump replacement?

Dewinator

Mine had similar issues when the throttle valve went south. Air and fuel issues can be hard to tell apart.

Johnny5Alive

Sounds like a bad tank of gas.

ducktails

I had the exact same issues with my 981 S, including the misfire code.

It should be noted that this problem occurred with at least 3 unique tanks of gas filled up at different locations. After driving for a while, I would get the PSM failure and Start/Stop failure. Turning the car off and on again would make the problem go away, for about a month. Then it happened on three consecutive days.

I tracked this car. The consensus is that the ignition coils fitted to this generation of car will go bad under high heat conditions such as those encountered at the track. I would not be surprised to know that the 991 uses the same coils as the 981S.

See: https://www.google.com/search?q=981+...utf-8&oe=utf-8

Just so that you know, once you can get them to agree that the coil is an issue, SOP at the dealer is to move the offending coil to another cylinder to see if the problem occurs again first, before they will replace it. Not cool if you track your car, the last thing I need is to go into limp mode in the corkscrew :P

siitech

Just checked my repair Invoice, the fault codes on mine were P1023, P1026, and P12al.

Homeles

Had the Engine Control Fault myself. Called the dealer and they had it towed in. When checked, they got misfire cyl. 5&6. It was reset and I left. Happened again about a month later. After 3 or 4 start cycles, it cleared itself. Checked again by the dealer with same results. Fast forward 1 year and again, I get the warning. This time they kept the car for 9 days to replicate the problem. No dealer had ever seen the problem before so my dealer was advised by Germany to reprogram the computers. So far after 9 months, no problem.

barney55

Well, if I've said it once i must have said it......hang on, i have only said it once.

These cars seem to have become way over-complicated,my 25 yr old,

964 seems to just keep on rockin, never even seen a fault code.

Hope it gets sorted.

Noah Fect

Sounds a lot like the ignition coil failures that have been reported on the 981s, most (but not all) of them with aftermarket headers with inadequate heat shielding. The coils are directly above the headers. Some products apparently don't include any heat shielding at all, which if true is just nuts.

The coils are relatively cheap, and IMO one of the 981 owners had a really good idea.

991carreradriver

What kind of oil is being used?

Stevie

Mobil 0W40, why?

Stevie

After a week of spirited driving in this steamy hot LI weather, the car has been driving without skipping a beet, supporting the bad gas theory.

Saturday, I drove to Limerock for another DE and filled up at the same Shell station that seemed to have cleared the issue. The exact same scenario occurred; The drive up perfect; first two sessions perfect; after the second it stumbled in the paddock and threw the same exact messages as I originally reported in my first post.

I drove the second and third sessions with full power except in the paddock. Drove home with AC and no issues (except for the remnant Fault Engine Control OK to Drive).

My next step is to try adding Techron to see if it is the injectors. I'll post the results_Steve