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Reved-Up Idle -- What's Your Diagnosis?

My 5-liter Cobra has developed a problem with its idle. It will, on occasion, soon after driving away after a start or sometimes a restart, rev up to about 1,300-1,600 rpms. No amount of throttling it hard, or moving the throttle cable will bring the idle down. The only thing that works is to shut the car off and restart it -- then it'll idle at a normal rpm.

All of the EGR/air idle control valve parts (everything connected to the EGR) were replaced with new Ford parts, and the throttle body was cleaned, just a couple years ago. The O2 sensors are also only a couple years old. (Note: I always/only use gas from a "Top-Tier" company -- Chevon or Shell.)

The check engine light has not illuminated, nor did any codes pop up when I scanned the computer.

My guess is a TPS (throttle position sensor). However, any TPS I've ever had a problem with always caused the engine to to not only rev up, but would also sometimes drop rpms/get close to stalling out.

What should I do/replace? Just throw a new TPS at it and go from there? Wait for the check engine light to illuminate? Mass-air sensor, perhaps? What are your thoughts?

Patrick

1993 Cobra (115K miles)
Reply to
NoOption5L
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When you find out, tell ME.

Now that I know about such things, I'm going to be cleaning out the MAS and IAB on a routine basis. But that doesn't affect my problematic idling. Doesn't want to keep running when I start it up cold, and (like yours) TFrog likes to idle high for a time, after a take it out of gear.

Something is screwing up the fuel/air mix, and I suspect electronics. And I suspect that I'm going to have to find someone who thoroughly understands this stuff.

dwight

Reply to
dwight

Oh, I will!

Mine is fine going to work in the morning, but when I start it up to leave work in the afternoon is when it acts up. I'll be driving down the road, kick in the clutch as I approach a traffic light or something and it be idling at 1,500. I can throttle it hard, and I've popped the hood and played with the throttle cable, but nothing has worked except to shut it off and restart it. Then it's fine, again.

It's a malicious computer virus that only attacks black 5-liter 1993 Mustangs. ;-)

Electronics you mean one of the sensors, right?

Patrick

Reply to
NoOption5L

When it idles up like that, hop out and yank the plug to the IAC and see what happens.

Reply to
WindsorFox[SS]

You're right, a bad/dirty one of these this could cause the idle problem. However, this is one of the parts I replaced only about two years ago with brand new factory Ford replacement part. Could it really wear out/get that dirty that quick -- using Top Tier gas and doing almost all highway driving?

Patrick

Reply to
NoOption5L

patrick I had the same problem.(high idle whenever it felt like it.) paid up for a new tps and presto, problem has never returned. no codes were tripped.

Reply to
dave

And your rpms never dropped and the car didn't stall or near stall, right...? (Because, again, mine doesn't) Only the ocassional high idle, right?

If that's the case, then you convinced my it's time for a new TPS.

Patrick

Reply to
NoOption5L

To answer my own questions...

Doesn't matter. Air Idle Control valves can/do wear out.

It likely won't unless the AIC goes way, way out of whack.

Bad guess. Better guess = AIC.

Buy a new AIC valve. Patrick '93 Cobra (with new Air Idle Control Valve on order)

Reply to
NoOption5L

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