My computer seems to be really a idiot on idling speed, it could start the car at 1, 200 and lower it down to 400 shortly after which may cause car shaking like a misfire (or maybe it does produce misfire then). So how could I tune the computer? Or is that caused by a bad spark plug? Thanks in advance! BTW, I just pushed my stang passing 140, 000 miles, adding 8000 during last 4 months.
Sounds like a dirty/bad IAC/ISC or a vaccum leak. I would start by cleaning he throttle plate and the IAC first, then look for dry rotted, broken, or disconnected vaccum lines.
locate the vacuum line leading to the EGR valve seloniod and the discontent it and plug it and if this fixes the problem then you kno whats bad but also it could be the EGR valve it self but the iac is a the best place to start.... hope it helps i had the same problem
