Mechanic did running OBD but found no code. Replaced fuel filter no luck. tried new ECM, distributor and other things no luck. It has fuel pressure “to” throttle body and spark during no run period. What’s the deal?
Is the idle air control (IAC) valve working correctly? The IAC controls idle speed.
The problem might be in the Idle Air Control circuit. There’s a component on the throttle body called an Idle Air Control motor. This component allows air into the engine and controls the engine idle speed anytime the accelerator is released.
The first thing to try is remove the IAC motor and clean it and the idle air bleed ports on the throttle body. Sometimes these become dirty where the IAC motor doesn’t go to the proper position, or the bleed ports become dirty and don’t allow idle air into the engine. If this doesn’t fix the problem, then it could be caused from a defective IAC motor.
Tester
Someone isn’t remembering their basic engine operations. Back to basics: When the throttle is released, the throttle plate goes to the idle position. When it does, the throttle position sensor (tps) tells the engine computer. Based on what the tps (rightly or wrongly) and other sensors tell it, the engine computer controls fuel injector action and the idle air control valve (iac) action, and engine timing, accordingly.
Use an MAF Sensor Cleaner on the MAF (Mass Air Flow) Sensor. Clean the throttle body bore and throttle plate, and iac passages with Throttle Body Cleaner.
Your mechanic can use his scan tool (or, multimeter) to observe the voltage patterns from the iac, tps, and MAF as the throttle is moved from the throttle stop to just off (1/4 inch) idle stop, and back. Erratic voltage patterns drive the engine computer gah-gah.
Use a vacuum test gauge on the engine to observe (in a diagnostic sense) engine intake vacuum as the throttle is moved with the engine running.
Thanks for the input, guys. We’ll look at it.
Don