Slight RPM surge - 986 Forum - The Community for Porsche Boxster & Cayman Owners

LEJ · 07-26-2016, 04:33 PM

The cruise control lever broke on my car so I bought a good used unit and took apart the steering to install the new (4) stalk combination switches. Once done, I had to reset the air bag light on the dash and I noticed that the engine, at idle, was surging a bit. Not much but noticeable. I removed the battery cable when I took apart the steering (don't need an air bag exploding) so could that have damaged something or is the engines management system confused? Any help will be appreciated.

tommy583 · 07-26-2016, 04:50 PM

The car will have to relearn it's settings after disconnecting the battery. Give it a few days.

LEJ · 07-26-2016, 07:42 PM

Thank you, I hope you're right

thstone · 07-26-2016, 09:00 PM

To explain a little more of what Tommy said...

Yes, it is very common for the engine to run rough after disconnecting the battery because the ECU settings were cleared. As the engine is operated, the ECU adjusts (learns) the engine settings to optimize operation. Those settings are stored in volatile memory so resetting the ECU clears them. Then when the engine starts again the ECU has to use the original pre-programmed settings which aren't optimal for an engine with a lot of miles and many years of wear and tear. The typical result is that the engine runs rough. The ECU will slowly adjust to the optimal settings again as you drive. Give it a few days or so of normal driving and everything should be back to normal.

kk2002s · 07-27-2016, 05:57 AM

I'm curious if Clearing the ECU should be done after changing Coil Packs
I just changed all 6 with new design.
Car seems to run as before but maybe it would be a benifit

LEJ · 07-27-2016, 07:09 AM

Tommy583 and THSTONE, Thanks, you were right, it's already running better after just a few miles of driving

LEJ · 07-27-2016, 07:12 AM

KK2002s You said that after changing the coil packs, the car seems to run as before.. (Did it run good or bad before and does it run good or bad after changing the coil packs??) If the coil packs were working correctly before you changed them then I seriously doubt it will run noticeably better after changing them..

kk2002s · 07-27-2016, 08:16 AM

LEJ - Car ran fine before. A couple pending Misfire CELs in the last few months motivated me to look at the coil packs and there were a couple cracked ones
I guess if it ain't broke leave it alone