Interesting info

[6670charger]

Not sure if anyone had heard of or done this, but I thought I'd share;

This past Wednesday, my exhaust fell down in the rear as the metal bracket had rusted away. Yes, I only had one connected as the stud on the other had broken a few years ago when I replaced the muffler; just never got around to replacing it until this week.

Anyway, the car has been running great (knock on everything in sight!!!!) since my head gasket change a few weeks ago, and was running great on Wednesday even after the exhaust dropped. After changing the exhaust brackets and hanger yesterday, I started the car and the engine started surging at idle. It also didn't want to run right away on startup. I know this is usually a vacuum related thing, but couldn't find anything under the hood that was loose. I know I torqued all the various bolts under the hood properly and had changed all the gaskets save for the oil pan when I did the engine. I had also changed most of the rubber hoses. My first thought was that maybe the O2 sensor in the exhaust got damaged when the muffler dropped, but I couldn't see any problem with the wiring or the connection at the pipe.

I stopped by my Indy down the street to see if they could shed any light or recommend something to look for. He couldn't see or feel anything loose or unusual under the hood, but suggested that I disconnect both the battery cables and touch them together (away from the battery terminals) for at least ten seconds saying that this will often reset the car's ECU and a few other electrical items.

Not knowing what else to do, I went home and did what he suggested and then reconnected the battery and started the car. No difference. I went in the house and did some computer research for about an hour, and then back out to the car to move it into the garage. Started her up......................no more problem! Started right up and then ran fine for a good 20 minute test drive and several test restarts, and running fine today so far.

So, if you're having an issue with your engine hunting idle, certainly check all of the Usual Suspects, but if nothing else seems to work, try disconnecting your battery and touching the connectors together for 10-15 seconds, then connect and let the car sit for an hour or two.

[YoungCR]

I had forgotten about this trick, thanks.

[jc43089]

I had a surging issue that came and went on my old e30 and it was due to a poor connection at the temp sensor causing excessively rich mixture.

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[jc43089]

It yes, sometimes it is necessary to reset ecu. I swapped a lightweight flywheel into an e36 and it would hardly idle, reset ecu and it was perfectly smooth again. It has a learning process to adapt to the specific engine. Pretty awesome technology for the time.

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