I have 91 ford mustang lx 2.3 when it idles it goes down to 500 rpm we have replaced the alternator, battery, fuel filter, fuel pump... We also cleaned out the IAC and the throttle body...
Clean the fuel injectors check for vacuum leaks and restricted exhaust
Ck throttle body for crap around the throttle plate,this will restrict air flow at idle, thus low RPM
I just cleaned both the throttle body and the idle air control valve
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