Rough idle after maintenance
Thread Starter
Advanced
Joined: Feb 2004
Posts: 51
Likes: 0
From: France
This car makes me mad.
I tried another "strategy" today :
- Disconnect the battery
- Ensure all is plugged and in a good condition
- Connect the battery
- Let the ignition on one minute then off 10 secondes (adaptation only for the DME ME 7.2, even mine is M5.2 but it takes just one minute to do).
- Start the car... still bad running, even stop one time by itself !
- Let it warming, when warm, carefully hold 3000 rpm for one minute
- Release throttle, the can now runs smoothly.
Now, the car runs fine.
After a short drive test, no problem and still smooth running.
Even if it's written in the workshop manual that "the engine must run for several minutes before the engine controle module can relearn the idle speed and mixture adaptations values", I don't know if it was only an "adaptation relearn" problem solved by running, for M5.2 DME, or a strange other thing.
Hope it lasts, but I don't really like a problem goes without I know why... Maybe my car is just smart and fix it by itself.
But really, I'm sorry for disturbing and wasting your time, just for telling then that my car now runs fine. I would prefer "to know exactly why". Hope you understand. Hope also I can help you again for anything else. 
I tried another "strategy" today :
- Disconnect the battery
- Ensure all is plugged and in a good condition
- Connect the battery
- Let the ignition on one minute then off 10 secondes (adaptation only for the DME ME 7.2, even mine is M5.2 but it takes just one minute to do).
- Start the car... still bad running, even stop one time by itself !
- Let it warming, when warm, carefully hold 3000 rpm for one minute
- Release throttle, the can now runs smoothly.
Now, the car runs fine.
After a short drive test, no problem and still smooth running.Even if it's written in the workshop manual that "the engine must run for several minutes before the engine controle module can relearn the idle speed and mixture adaptations values", I don't know if it was only an "adaptation relearn" problem solved by running, for M5.2 DME, or a strange other thing.
Hope it lasts, but I don't really like a problem goes without I know why... Maybe my car is just smart and fix it by itself.
But really, I'm sorry for disturbing and wasting your time, just for telling then that my car now runs fine. I would prefer "to know exactly why". Hope you understand. Hope also I can help you again for anything else.
Race Director
Joined: Sep 2006
Posts: 19,031
Likes: 266
From: Bentonville, AR
After running the car several minutes after my first problem, with the correct plugs, it disappear and the car runs perfectly after for some month. But this rough idle occurs one more time between today and my first problem. After checking the coil resistances, one were different to the others. After replacing it, as the first time, after a little road test, all was fine.
The car is parked indoor, and safe. I was joking about the mouses but obviously, I visually checked plugs and harness. I didn't think that the MAF fails because I would have not only problems at the right side cylinders. I also checked the value measured and it increases as I push the throttle. The air temperature seems also to be fine.
Car running, I checked the O2 sensor values : one changes during throttle actuation, other one stays at 0. I will checked futher about it, but maybe is there my problem. I will let you know.
Thanks !
The car is parked indoor, and safe. I was joking about the mouses but obviously, I visually checked plugs and harness. I didn't think that the MAF fails because I would have not only problems at the right side cylinders. I also checked the value measured and it increases as I push the throttle. The air temperature seems also to be fine.
Car running, I checked the O2 sensor values : one changes during throttle actuation, other one stays at 0. I will checked futher about it, but maybe is there my problem. I will let you know.
Thanks !
I'd still not replace the MAF the first thing with one bank of misfires as the only symptom.
If the symptom repeatable then disconnecting the MAF from the wiring harness and seeing if the symptoms reappear is one way to possibly eliminate the MAF.
Lastly, my experience has been the amount of air being reported by a bad MAF can be ok. The intake air temperature reported by a bad MAF can be reasonable.
What I have seen is the short term fuel trims occasionally go rail to rail. That is the readings go from -25% to +25% and all points in between. When the MAF goes bad. However the MAF doesn't always fail outright but just develops an intermittent fault/failure. At other times, the MAF works just fine and the short term fuel trims are reasonable.
But when one observes the MAF's adaptation values are all over the place and not in some reasonable order -- by reasonable order I mean the adaptation values climb in increments from 0 to 25% and then go back down to -25% as opposed to the adaptation values take on the output of a randon number generator -- this is a pretty good sign the MAF's bad.
An outright failure of a MAF could of course deliver more concrete symptoms of it being the MAF that is bad, but my limited experience with bad MAFs is the more intermittent failures are more common.
Sincerely,
Macster.
Drifting
Joined: Dec 2009
Posts: 2,919
Likes: 3
From: Aiea, HI
I didn't see an answer to ivangene's question so figured I'd mention how fuel goes bad through time. How old is the fuel?
Fuel sitting in injectors and lines will gum up when evaporating from just sitting there. Yes the fuel doesn't need to of been exposed to air to gum injectors and lines.
Thread Starter
Advanced
Joined: Feb 2004
Posts: 51
Likes: 0
From: France
Even the car isn't a daily driver, it is regulary driven. But probably not enough, you're right. The car doesn't stay not running for a long time. Max in winter, sometimes 2 or 3, maybe 4 month without being drived (sometimes, we let the engine running). That's why I have to charge the battery (or because I let the door a little opened
). Maybe the fuel isn't good as before, but when my problem disappears, it's still the same fuel.My problems always go after running everytime it occured. I couldn't never had a car in this state for many months !
Maybe my AFM is dirty, and the "factory settings" resetted by the battery disconnection make the engine bad running because of wrong mixture. Let it running makes the modification in the correction, and then it can runs right. Maybe it's another thing wich can be corrected after some minutes of running.
Can a 996 be so intelligent ?
Not really sure but it shows me all signs of it. Nice car. 
Drifting
Joined: Dec 2009
Posts: 2,919
Likes: 3
From: Aiea, HI
Pretty frustrating. Could be a lot of things. I've had fuel pumps before they fail cause rough running on and off for months. Anyway the best thing to do for an electronicly controlled mixture and all is to set it up with proper fueling and spark. When trying what's easy and doesn't require major work on the engine the changing the fuel is a good option. A year old fuel is bad fuel. The electronic changes the ignition does to adjust mixtures and such would be adjusting to the max till it can't calibrate far enough with bad fuel. I think bad fuel would be prone to burn better in a hot engine. Even gummed up injectors probably function better when the gum is loosened by heating. When putting new fuel in there add some fuel system cleaner for the injectors. Like a lot of things its a combination of variables. There are fuel system flushes that can be used which I can't remember the name of. Lots of performance bike riders run into problems with fuel after winter storage.
All in all I figure if your fuel was a year old and you replace it the engine will run better with just that change. Don't forget to add some injector cleaner before fueling.
All in all I figure if your fuel was a year old and you replace it the engine will run better with just that change. Don't forget to add some injector cleaner before fueling.
