So I did a bunch of mods today. 160 thermostat, throttle body bypass and threw in an air foil while it was all apart. Also cleaned the MAF sensor and the intake.

I disconnected the battery for about 6 hours. When I restarted the car I thought it was going to start stalling on me. VERY rough idle, whole car was shaking, idle going up and down...

After about a minute it kicked into high idle and ran like a top again.

Everything runs great now but I suppose I am just curious if when the battery is disconnected for awhile if the PCM starts from scratch and reprograms everything?

 

The PCM clears immediately when power is disconnected. Volatile memory is primarily long term fuel corrections (BLM's), learned idle air control (IAC) minimum stieps, and stored trouble codes. Nothing related to the program is lost. Probably struggled to find the right position for the IAC. BLM's will be relearned when the engine and O2 sensors warm up and the PCM enters closed loop, and can use the O2 sensor feedback to adnust the A/F ratio. If your PCM was having to make large fuel corrections at idle using the Cell 16 BLM, it could have contributed to the rough idle, typically for about 206-seconds. You will have to drive the car until you operate in the many specific cells defined by RPM and engine load. Each cell will be relearned as you drive.

 

Thanks Fred!
Guess I'm going driving tomorrow!

 

The only other things that need to "reset" after disconnecting the battery that Fred mentions is the "IM" (emission) monitors. There are 8 and after driving the car for a few hundred miles all reset. Operationally there is no effect on the car however if you have plug in emission testing you should not get the test done until you drive the car under normal driving conditions for a few hundred miles as the drive cycle takes some time to get all of the IM's to read "ready" aka "pass"

 

Chimera96, thanks for the heads up.
Fortunately we don't have emissions testing where I am from. But after reading your post I can see how that could be a problem for some people and it is good advice.