I have a 04 g35 sedan that just hit 200000 miles. I just recently changed valve cover gaskets, oil and filter, tranny flush, spark plugs and coils. Now i have random codes that will pop up on start up. I've checked all my plug ins, sensors, vaccum hoses etc. and all seem locked tight and clean. Never the same code when check engine light comes on. I recently heard about a ECU reset but not sure of the correct process. Need help please.

 

ECM reset will CLEAR the codes and reset your long term fuel trim, that's it. If codes come back it's because the ECM found problems.

Without posting the codes there's no possible way we can help. Each code is a very SPECIFIC problem the ECM found, they all have their own various steps to troubleshoot, there is no "one size fits all" troubleshooting.

You want to get those codes before you reset the ECM though. I'm guessing there's a large vacuum leak because either the oil fill neck got pinched between the upper and lower plenum, or you merely forgot to plug something in, or you got two of the coil pack harnesses backwards.

ECM reset is easy, disconnect the battery, pump the brakes a couple times, wait 10 minutes, plug the battery back in. Your alarm will go off, disarm it with the fob unlock button.

 

I do have about 15 different codes printed. I didn't list because once i shut off car and it sits for a couple hours the check engine light goes away and it drives fine. By that night or the next day the car has a random low idle under 2000rpm attempting to stall out but doesn't. Thank you for the info and will try the reset and see what changes.

 

Did you ever try following the troubleshooting steps for each code in the FSM?
It might be a good idea to start there?

 

Post the codes anyways, I'm usually pretty good about "working my way back up the waterfall" to give you an idea about which code/s are actually causing the cascade of error codes.