Rough running fixed by engine braking?

[d00df00d]

Just wanted to get some thoughts from BITOGers on what happened. Read this and let me know what you think.

My car had been sitting for a few weeks so I decided to take it for a little drive around the neighborhood. Turns out the battery had died, so I needed a jump. My brother and I got it running after a few hard starts and a stall from idle, and I set out for my drive. It maintained idle RPM just fine, but the engine was running a little rough and it took more throttle than usual to start from a standstill. This continued even several minutes after the coolant had reached operating temp. I also had a check engine light. Understandable.

What I don't understand is what cured the rough running and weakness: after 10-15 seconds of engine braking in 3rd gear from around 3,000 RPM, the engine was butter smooth and ran normally (although I still had a check engine light).

Thoughts?

 

[Deltona_Dave]

I am no expert, but have had a few batteries die. Seems like your engine computer needed some time to "relearn" it's settings after losing electric power for some time. I just had to change the battery in my Titan and let it idle for 15 minutes, then drive around for 20 minutes or so. Ran poorly for a few minutes, then it remembered.

Just my .02
Dave

 

[ls1mike]

Originally Posted By: Deltona_Dave
I am no expert, but have had a few batteries die. Seems like your engine computer needed some time to "relearn" it's settings after losing electric power for some time.
Just my .02
Dave

Bingo, I just had the Buick apart for the LIM and it sat for a week with the battery disconnected, a few rough starts, some idling and driving for the "relearn" and presto! Smooth as silk.

 

[saberz]

Some cars need to have the computer re-learn air/fuel mixtures when the battery is disconnected for a certain period of time. The Xterra can relearn the amount needed by the way you drive. Thats why many people recommend when buying a used car to disconnect the batter, reconnect it after some hours and let the car idle for 10 minutes.

Then drive the car as you would normally drive for a few days and it will adjust the mixture to your style. This helped with some MPG problems on the Xterra due to the computer.

 

[d00df00d]

I fully understand all that. What I am wondering is why the problem suddenly went away when I engine braked for 10-15 secs. Any ideas?

 

[cchase]

Something vacuum related perhaps cleaning itself out?

 

[Scott_Tucker]

It may be that you had an ignition misfire that cleared up after a few minutes of running. Is this your M3? It may have spark plug boots that are starting to leak. This is pretty common on coil on plug vehicles.

 

[d00df00d]

Yes, this is the M3.

I haven't checked the coils and plugs yet. It needs a little bit of work in the coming weeks though (which is why it has been sitting) so I plan on doing that then.