General Ford Ranger Discussion General discussion of the Ford Ranger that does not fit in any other sub-forum.

Idle Air Control cause of starting stall?

Old 02-19-2019
Thread Starter
Join Date: Mar 2017
Location: Seattle, WA
Posts: 86
Idle Air Control cause of starting stall?

1992 Ford Ranger Custom 3.0 V6 Automatic 6ft bed

Ive done a lot to this Ranger, Ron knows more than half of it I think. Recently repaired a fuel line I caused a pin leak from. After that my fuel pump died on a snow day. Replaced that, very old, had a broken black wire at its connector.

anyway the day after replacing the pump I got check engine codes everytime I drove. I found the FPR (pressure regulator) had a broken vacuum line. I repaired this. Now I get no check engine codes. Still runs the same though. When I cold start I HAVE to give it a little gas for 10 seconds before itíll idle on its own. Hasnít always been like this, but has been for some time now. Always drives and never has codes due to this.

I pulled the IAC electrical connection while running it today. It did NOT change the idle or anything else. Does this confirm an IAC issue? Before I knew much I did take this off and had cleaned it, no change happened back then and it actually was already clean.
Old 02-20-2019
RF Veteran
iTrader: (1)
Join Date: Jan 2014
Location: Vancouver, BC
Posts: 12,752
Yes, most likely IAC Valve issue
Take it off again and test if it is working by applying 12v and ground(from your battery) to its two pins, there is no polarity, Valve inside should move OPEN and then when 12v is cut it should move closed.
If IAC Valve doesn't move when you apply power then replace it

Also with a volt meter set for DC Volts test the IAC Valves wires, Red wire should have 12v with key on, other wire should be a Full Ground with key on engine off, so test that you see 12v with both meter probes hooked to the two wires.

Computer controls the Ground(other wire) to the IAC Valve to vary its voltage to open and close it to set air flow and idle RPMs, this method is accurate within +/- 3RPM
When key is turned on Red wire on IAC Valve gets 12volts from PCM relay, the computer will Ground the IAC Valve to open it all the way for startup, this is why ALL fuel injected engines should REV on startup, usually 1,500-1,800rpms then computer starts to close IAC Valve to set cold or warm engine idle

Computer uses ECT(engine coolant temp) sensor to detect engine temperature, so if ECT sensor should be failing and "telling" computer coolant is warm, 150deg say, then computer would set low idle, thinking its just a restart after sitting a few minutes, would still get the REV up on startup, if IAC valve is working

ECT sensor has no connection to dash temp gauge, thats controlled by ECT SENDER, separate device on the engine
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