rough idle after battery change
 

I have a 1999 C230K with approx 68K miles. Last Sunday, the battery was dead and the starter wouldn't crank. I jumped the car and it drove fine the rest of the day. The next day, it seemed to be cranking a little slow, so I took it to my indie to check the battery. He replaced the OEM battery with an Interstate and immediately upon leaving the shop, the "check engine" light came on and the car started idling roughly. I took it back to the shop, they checked and thought it was the computer system in the car resetting itself. Indie told me to drive it for a week and see if problem persists. The car drove fine for one day and then started idling rough and check engine light came on again. It seems to only run rough when idling, not at higher speed. Any thoughts?

The fuel computer constantly changes the fuel mixture & adapts to sensor imputs. IF the battery goes dead & is disconnected then the fuel computer must re-adapt to the sensors again & that takes 10-50 miles of (light footed) driving to accomplish.

What codes come out of the computer?? P0170/173 are for fuel trim & mean that the DME/air mass sensor correction at limit.

Thanks for your reply M.B.Doc - They didn't tell me what the codes were, but did mention that it showed something with the number 4 cylinder. The indie shop owner said he didn't see how the battery change could affect a cylinder and that's why he thought it would adjust itself within a week. I will remind my wife to be "lightfooted" for the next several miles. Hopefully, your explanation is correct - the car ran perfectly before the battery was disconnected. Thanks again. BTW, any problems you know of using the Interstate battery instead of OEM?

http://www.peachparts.com/shopforum/tech-help/95945-98-c280-w-64k-bad-airbag.html

You might be interested in the post from "BLACKMERCEDES" in this thread.

Dan

OUCH! - I followed the "jump start" instructions in the manual carefully. I would hope that if a significant possibility existed that damage could result from jump starting the car, the manual would advise not to do it - not give instructions on how to do it.

I would think you are OK if you followed the instructions in the manual. BUT...It also looks like there is potential for some damage during this operation. I suppose you just have to weigh the risk VS the benefit and do what you think is best.

Dan

Update - my wife reports the car seems to be running fine now - I guess (hope) the problem was as diagnosed by M.D.Doc. I admit that after reading some of the info posted, I am now paranoid about jump-starting. Thanks, guys, for the input!