Need help with Revving motor

[ndalake]

Hello, I need some help. I have a '89 GT with a 5 spd, AC, runs really good most of the time with normal rpm's under idle at about 800 - 1000 rpm's, then after about 45 minutes of driving, the car will idle up to about 2000 rpm's and hold there. It doesn't go up anymore and doesn't come back down either. Once it begins to rev high, you can turn the car off and start it right back and it goes right back to 2000 rpm's again. It's really annoying at a red light with flowmasters! The check engine light does come on randomly, just about everyday after about 20 minutes of driving. Is this a MAF problem, a ECU problem or something else? Is the check engine light connected to this issue? When I purchased the car used in September, it didn't do this. It has developed this issue over the last couple of weeks.

Does anyone else experience this?

Thanks for any help you can provide.

 

[HISSIN50]

You answered your own question - grab them codes and take a little guesswork out of it. Jrichker has a couple of sites that go into pulling codes if needed.

Good luck.

 

[robertdale]

I had the same problem with a bad Throttle position sensor. Might want to pull codes and check TPS voltage.

 

[txstang84]

ck the IAC too...

 

[superhuaman]

+1 for the iac. if the tps causes a high idle, it will not return instantly upon restart.

 

[HISSIN50]

If you stop some place safe when it decides to idle up, you could disconnect the IAC electrical connector and see if the idle drops. If it does, that would be telling.

Good luck.

 

[jrichker]

You guys with idle problems could same a lot of time chasing your tails if you would go through the Surging Idle Checklist. Over 50 different people contributed information to it. The first post has all the fixes, and steps through the how to find and fix you idle problems without spending a lot of time and money. I continue to update it as more people post fixes or ask questions. You can post questions to that sticky and have your name and idle problem recognized. The guys with original problems and fixes get their posts added to the main fix.

Your problem is covered in the sticky. Check it out.

 

[87ttopstang]

I had the exact same problem a few years ago. Put on a new IAC and it fixed the problem.

 

[ndalake]

Thank you all so much for your insight and help. I thought the company where I work had a lot of acronym's, they've got nothing on this group. I tried to find info about this prior to posting and had no luck. I'm going to go read this info and get educated before I ask anymore stupid questions.

Thanks a bunch.

ndalake

 

[seijirou]

Thank you all so much for your insight and help. I thought the company where I work had a lot of acronym's, they've got nothing on this group. I tried to find info about this prior to posting and had no luck. I'm going to go read this info and get educated before I ask anymore stupid questions.

Thanks a bunch.

ndalake

Not a stupid question chief, nobody popped out knowing this stuff. Sometimes you need to ask some questions to see how much there is to learn.

The IAC is the Idle Air Control valve. It's the cylinder that's bolted to the side of your throttle body. When it's open, air can go around the throttle body blade. The computer uses it to control the idle rpm.

The TPS is your Throttle Position Sensor. Which is just as it sounds, it lets the computer know what position the throttle is in. Be it opened or closed or somewhere inbetween.