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Car Forum / Ford / Ford Mustang / December 2006Reved-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) > 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, [quoted text clipped - 22 lines] > Patrick > 1993 Cobra (115K miles) 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 > > 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? > > 1993 Cobra (115K miles) > When you find out, tell ME. Oh, I will! > 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. 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. > 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. It's a malicious computer virus that only attacks black 5-liter 1993 Mustangs. ;-) Electronics you mean one of the sensors, right? Patrick >> 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 [quoted text clipped - 6 lines] > > Patrick When it idles up like that, hop out and yank the plug to the IAC and see what happens.  Signature"Trespassing on private computer networks through intentional misrepresentation is an activity that merits no First Amendment protection" - Judge James W. Haley Jr. "And now Dib I leave you to your.... Moosey fate!" - Invader Zim > >> 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 [quoted text clipped - 4 lines] > > > > Electronics you mean one of the sensors, right? > When it idles up like that, hop out and yank the plug > to the IAC and see what happens. 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 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. > 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, [quoted text clipped - 22 lines] > Patrick > 1993 Cobra (115K miles) > 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. 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 > > 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, [quoted text clipped - 22 lines] > > Patrick > > 1993 Cobra (115K miles) To answer my own questions... > 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.) Doesn't matter. Air Idle Control valves can/do wear out. > The check engine light has not illuminated, nor did any codes pop up > when I scanned the computer. It likely won't unless the AIC goes way, way out of whack. > 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. Bad guess. Better guess = AIC. > 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? Buy a new AIC valve. Patrick '93 Cobra (with new Air Idle Control Valve on order) |
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