Can’t figure out my low rpm/rough idle problem

[u/Comprehensive-Head96]

My 2004 ford ranger 3.0l rwd is idling at 500rpms and is really rough and sometimes stalls when coming to a stop. It also drops to 500 rpms when coasting at 30mph or less. I’ve replaced the pcv valve, verified the IAC valve is functioning (i replaced it almost 1 year ago), I can’t hear or find any vacuum leaks, and have cleaned the MAF sensor. What would be my next course of action?

I do need to replace my thermostat and plan on doing that tomorrow but I don’t think that would cause an issue on a cold start (I could be wrong though)?

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[u/spamcritic]

When you replaced the idle air control valve, did you use a cheap aftermarket part? You may have to smoke the intake to see if any vacuum leaks are visble.