97 high idol - Ranger-Forums - The Ultimate Ford Ranger Resource


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Old 1 Week Ago
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97 high idol

Okay for the pros out there, my 97 2.3 when you start it even if it's warmed up 95 degrees out it doesn't matter it revs about 2500 to 3000 even if you just shut it off, I warmed it up check for vacuum leaks there are none any ideas
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After it was warmed up and idling, did you unplug the IAC Valve's 2 wire connector?

Thats how you check if there is a vacuum leak

Unplugged the IAC Valve will close and RPMs should drop to 500 or so, under 600
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97 2.3

Yeah Ron did exactly what you said and it's slowed down the engine so much it actually died, I am mechanically inclined I just I'm from the old days and you know like a 68 Impala I could figure out
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Well if the IAC Valve is setting the idle that high then computer is the issue, or its wire to IAC Valve or internal short to ground inside IAC Valve.

Control for IAC Valve is a pulsed Ground
When key is turned on IAC valve gets 12v on Red wire, and the computer boots up, and then Grounds the IAC Valve, so it opens all the way for start up
This is why ALL fuel injected engines SHOULD rev up when started, air valve is opened all the way
When RPMs are above 400(engine started) computer then starts to Pulse the Ground for the IAC Valve, this is the same as lowering the voltage to the IAC Valve, so it starts to close, RPMs drop.
Computer then sets "target" RPMs for idle, these are set at the factory and are engine temperature based, the colder the engine the higher the idle.
Fully warmed up target idle can be 650 manual trans, 750 automatic, but this changes by year because of emissions standards, higher idles have less emissions, also if Defrost or AC is on idle will be higher

The IAC valves voltage to RPM is Learned by the computer over a few drive cycles, computer has engine RPM data from crank sensor and a "target" RPM, so it varies the IAC Valves voltage to match target RPMs then "remembers" that voltage, so it can return to that voltage without "hunting" for correct voltage.
Correctly working computer/IAC Valve setup will stay within +/- 3RPM of target


You can use sewing needles and pierce the two wires on the IAC valve, then test with volt meter, the red wire should have 12volts key on, the other wire goes back to the computer and is the Ground.

Test red wire, engine running, to engine ground, should read system voltage, like 13.6 volts
Then use other wire as the Ground for volt meter, should read lower voltage, like 8 volts, if its the same 13+ volts then other wire is shorted to ground , in wiring harness or in the computer
And it is possible the IAC Valve is shorted to ground internally.
Engine and key off
Unplug IAC Valves 2 wire connector
Use OHM meter to test for internal short
Put one probe on IAC Valves metal case and touch the other probe to either terminal, neither should show a connection to case, i.e. low OHMs
If Valve tests OK then put 1 probe on engine ground and other probe on Non-Red wire in IAC Valve connector should read high OHMs or N/C(no connection), if low ohms then move wiring around, there could be a short to ground in the wiring harness.

Last edited by RonD; 1 Week Ago at 11:19 AM.
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