Hello all, im trying to find if anyone has any leads as to why my ranger idles up and down randomly. Ive already replaced my map sensor, idle air control valve and PC valve. Any info would be greatly appreciated. Thank you

 

Welcome to the forum

For future reference, please include year and engine size with questions
1988 2.9l

And did you check the MAP sensors vacuum line?
It needs to be "air tight"

Also is the idle high and stable when engine is COLD?
And the wandering only starts when its warmed up?


After engine is warmed up and idling
Unplug the IAC Valve
Idle should drop down to about 500-600rpms, barely running, engine may even stall, we can deal with that if it does

But main reason to unplug the IAC Valve is to see if the Computer is what is doing the wandering idle, by opening and closing IAC Valve

Or if the computer is just try to stabilize the idle

If engine stalls, look on the throttle linkage for the Anti-diesel screw, looks like an idle screw, give it a 1/2 turn clockwise and restart engine, see if it will idle at 500-600rpms now, still no IAC Valve
If not try another 1/2 turn

If you have a stable idle with no up and down, plug IAC valve back in and see what it does, if it starts to go up and down the IAC Valve or computer is the issue

If idle is still going up and down with no IAC Valve, then remove PCV Valve hose and block it with your finger, see if idle stabilizes, PCV Valve is a "controlled vacuum leak" but can get uncontrolled, lol
Remove each vacuum hose from intake and plug the port with your finger to see if that hose/device has an air leak