High idle after freeway driving

heavy4x4 · July 22, 2005

Anyone else get this?

I just went on an hour drive on the freeway and had the A/C going. When I came to a stop, my idle was at around 1200-1300 rpm. It didn't go down the remaining 2 miles I had to get home. After the vehicle sat for 30 minutes parked in my driveway, I started it and idle was back to ~500rpm.

Is this normal?

-Steve

Bish · July 22, 2005

Anyone else get this?

I just went on an hour drive on the freeway and had the A/C going. When I came to a stop, my idle was at around 1200-1300 rpm. It didn't go down the remaining 2 miles I had to get home. After the vehicle sat for 30 minutes parked in my driveway, I started it and idle was back to ~500rpm.

Is this normal?

-Steve

<{POST_SNAPBACK}>

I would say no it is not normal. Mine has never done that in 148K.

What year/model is your truck?

71GMC_3/4T · July 22, 2005

My '92 Chevy Z-71 did this when the O2 sensor was loaded up with crud from a fouling plug.

Raymond Lowe · July 23, 2005

Anyone else get this?

I just went on an hour drive on the freeway and had the A/C going. When I came to a stop, my idle was at around 1200-1300 rpm. It didn't go down the remaining 2 miles I had to get home. After the vehicle sat for 30 minutes parked in my driveway, I started it and idle was back to ~500rpm.

Is this normal?

-Steve

<{POST_SNAPBACK}>

It's not normal but not unheard of if you have a standard transmission. Sometimes an O2 sensor can sense a condition it doesn't like and call for a higher idle for a brief period of time. Even brands of fuel can impact this. If it doesn't go away then try cleaning the throttle plate.

PFarkas · July 23, 2005

Anyone else get this?

I just went on an hour drive on the freeway and had the A/C going. When I came to a stop, my idle was at around 1200-1300 rpm. It didn't go down the remaining 2 miles I had to get home. After the vehicle sat for 30 minutes parked in my driveway, I started it and idle was back to ~500rpm.

<{POST_SNAPBACK}>

It could also be an IAC problem.

Other people have posted with a similar problem - I'd link to a message thread, but the Search hates me....

heavy4x4 · July 23, 2005

Anyone else get this?

I just went on an hour drive on the freeway and had the A/C going. When I came to a stop, my idle was at around 1200-1300 rpm. It didn't go down the remaining 2 miles I had to get home. After the vehicle sat for 30 minutes parked in my driveway, I started it and idle was back to ~500rpm.

<{POST_SNAPBACK}>

It could also be an IAC problem.

Other people have posted with a similar problem - I'd link to a message thread, but the Search hates me....

<{POST_SNAPBACK}>

Search hates me too...that's why I posted

Butch 02 Denali · July 23, 2005

If the PCM senses high tranny or engine temp, it will raise the idle to speed up the water pump. I bet that's what happened!

DEV1ST8R · July 23, 2005

The search hates everybody

mmmikkke · July 24, 2005

But new servers are only a month or so away, and then seach will be over its period.

heavy4x4 · July 24, 2005

If the PCM senses high tranny or engine temp, it will raise the idle to speed up the water pump. I bet that's what happened!

<{POST_SNAPBACK}>

Engine temp and oil pressure look good.

If the tranny temp was high enough to make my truck do what it's doing, don't you think it would throw the "high trans temp" message in the message center thingy?

-Steve

I'm leaning toward IAC as I've gotten some good advice on that being the problem. I'll see if my problem continues (it doesn't happen all the time, usually when it's hot out and I have the AC on).

Truckdog · August 27, 2005

I have a 2000 Silverado 5.3 4x4 and it is doing the same thing. The rpms will just increase and stay there. Sometimes 1000 and some time more. It was running 50 MPH with no pedal. I pretty sure the throttle is not sticking. I can cut it off and go crank it again and it's back to 500 rpm. I heard the O2 sensor could make it overfuel? I'm looking for answers also.

CapitalTruck · April 20, 2006

Did anybody ever find a solution for this? My 2004 4.8 is having the same problem. I think it's going to wear my brakes out faster!

HotWheels301 · April 20, 2006

It could be the IAC, but I certainly wouln't rule out the Throttle Position Sensor. It happened to me on my 2000 Mustang GT and that's what it turned out to be.

heavy4x4 · April 21, 2006

Sorry I never posted an update to this topic, everyone.

I did end up fixing this problem by cleaning the Idle Air Controller. I'm not sure about everyone else's truck, but the intake area of my engine is coated pretty well with some heavy carbon build-up. I cleaned the carbon build up out of the IAC and fixed my high idle problem.

To do this:

- Disconnect the wires and remove the two torx screws on the IAC (when looking at the engine, the IAC is the black thingy at about 2 o'clock on the throttle body) - I actually ended up removing the entire throttle body so I could get at the second torx screw (thanks GM)

- Spray carb cleaner onto the plunger of the IAC to break up the carbon - wipe out whatever you can with a rag

- My Haynes manual states you shouldn't manually push the plunger in on an old IAC, as you might break it

- Bolt everything back up and you're good to go

- While you're in there, clean out the carbon that has built up inside the throttle body where the butterfly valve/throttle blade seats. This will solve any "sticky pedal off idle" issues.

Good luck. I won't guarantee this will solve your problem, but it certainly solved mine. I guess I'll probably have to clean the IAC again some time in the future, but probably not any time soon.

-Steve