Idle problem

[Hopeless]

My 2001 Sierra 5.3 has recently began having an intermittent idle issue, but the check engine light is not coming on.

Starting in the morning and driving to work is fine. Occasionally driving back home after work it will start to feel like it's "pulling" harder then normal. When this happens after putting it in park the idle jumps to 1000 - 1200 rpm, putting it back in drive the idle falls back down to 500-700 rpm.

Last weekend I bought some MAF cleaner and throttle body cleaner to clean both. I didn't remove the throttle body, just cleaned it the best I could with it still on the motor. Since then it's been fine until last night it did it again.

From what I've read I'm thinking the IAC valve is either going bad or gummed up and not working correctly. Anyone have any other ideas?

 

[dave_the_nerd]

I had similar problems years ago, and it was the IAC valve thingy. Problem was initially pretty intermittent, but got worse over a period of 1-2 months.

For an '04 Saturn Ion, that's a $60 part that took about ten minutes to replace.

It did, however, take a couple miles worth of driving to calibrate the new one. I knew that in advance, but it was pretty freaky. I replaced it in my friend's garage - initially, my 'new' idle speed was 4k rpm in neutral. I put it in gear, drove home, and by the time I got back to my apartment (~5 miles away) it was as good as new.

 

[Raizinman]

I would suggest you check and likely will need to clean the throttle bore. This normally takes care of most of the low or poor idle complaints.

 

[Hopeless]

Update

I didn't mention it in the op but every time I did something I started by unhooking the negative battery cable.

Replaced the IAC. Made it only a few days and started having the issue again. For whatever reason though the idle in park wasn't going as high as before, only going to 900 - 1000.

A couple weekends back replaced the TPS and PCV. Made it over a week now and hasn't happened again.