text: Idle problem, RPMs keep increasing! - '00 GT - Ford Mustang Forum
  Ford Mustang Forum > Ford Mustang Model Specific Forums > 4.6L Mustang Forums (1996-2004) > 4.6L Tech > Idle problem, RPMs keep increasing! - '00 GT
  post #1 of 9 (permalink) Old 08-20-2013 Thread Starter
  Idle problem, RPMs keep increasing! - '00 GT
  I have a 2000 GT, 168k, 5sp. Just the other day I was coming to a stop in my driveway after work and I noticed my RPMs weren't coming down to normal idle. They were around 1300rpm. I tried revving to see what would happen and they just kept increasing and wouldn't come back down! I had to just shut off the car and I'm afraid if I shut it off when it's revving to high I might damage the internals. This happened again tonight so I'm looking to have this fixed right away.
  I was thinking maybe a bad TPS? IAC is fairly new, less than a year old. I haven't cleaned MAF in a while, I'll try that too. Any other possible culprits?
  post #2 of 9 (permalink) Old 08-20-2013
  Check the iac, throttle body and any vacum leaks
  post #3 of 9 (permalink) Old 08-20-2013 Thread Starter
  I know for a fact that it isn't my IAC. I will check for vacuum leaks and clean the MAF and throttle body.
  post #4 of 9 (permalink) Old 08-20-2013
  I know you said the iac isnew but make sure its not a defective one.
  post #5 of 9 (permalink) Old 08-20-2013
  While experiencing the issue, unplug the IAC electrical connector. What happens? If the engine stays running, go buy a new one - Motorcraft if at all possible (check rockauto, they usually have oem stuff like this and prices usually don't make your piss boil).
  Being that the Idle Air Control does just exactly as it's name implies, I'm leaning on that for now. Vacuum leaks usually produce a low unsteady idle, and TPS are rare to have issues and generally have different symptoms when they do. As far as replacement IAC's, I've heard before that certain brands sold by parts stores aren't destined for greatness, so I'm kinda thinkin that's what's happening to you.
  post #6 of 9 (permalink) Old 08-20-2013
  Start by checking the throttle return spring at the throttle body! Its probably not the problem, but you need to be certain of that before anything else. I would even check the cruise control stuff, the rpm's climbing and not coming back down is not a common problem and definitely serious.
  If the revs are climbing and you can't stop them shutting it down is the best thing you can do. The spark and fuel are cut off, but as long as the engine turns the oil and water pump turn so you will do less damage than anything else you could do.
  As as most things for your Mustang go the aftermarket is better and costs less than stock. In terms of sensors, OEM is the only way to go.
  post #7 of 9 (permalink) Old 08-20-2013
  It's a small crack in the vacuum lines. I had the same problem! Visually inspect the line from the firewall all the way to the throttle body and fuel solenoid.
  post #8 of 9 (permalink) Old 08-23-2013 Thread Starter
  Thanks for all of the replies guys! It hasn't happened since I posted this thread so we will see how it plays out! Definitely unplugging the IAC will be the first thing I try. I did buy Motorcraft so hopefully it isn't a defective.
  It makes me feel a little better knowing that shutting it off is the best thing to do.
  post #9 of 9 (permalink) Old 09-14-2013 Thread Starter
  Well guys it happened again tonight...I did what you said and unplugged the IAC and the engine reminded running. The idle went WAY down though. I went from sitting at 2300 to 500-650 until I finally shut off the car. I will be checking my receipt for the warranty on it.