High Idle Issue with my TrailBlazer

[Black08TB]

08' TrailBlazer with 4.2ltr I6

On cold starts it will idle at 1000-1100 RPM and drop to 900 RPM in short order. After driving and coming up to operating temperature, when I come to a stop and the truck is at idle in gear it will be back to normal around 600 RPM. So now the warmer weather is here and it still acts like it's Winter time on start up. I'm wondering if there is a sensor that tells the engine / computer what the ambient temp is outside and how to moderate the EFI system? I imagine it's a wide range sensor so it maybe malfunctioning but still be in it's operating range, so there would be no trouble code just inaccurate temp readings. Anyone ever have such a problem?

Also, when I shut the truck down after a 30 minute ride home from work and restart it 15 minutes later it will high idle again like it was a cold start and drop again once again after idling or driving a bit.


Thanks for any help you guys can offer!

 

[Mounce]

Mine does the same thing. I don't worry about it.

 

[littleblazer]

Mine holds 750 after a minute or so. After the air pump shuts off

 

[Mounce]

Luckily I don't have SAIS but it's always done exactly what the OP describes.

 

[Black08TB]

Well at least I'm not alone with this little problem!

 

[coolasice]

Completely normal

 

[Black08TB]

Completely normal

No offense, but I disagree. I've had the truck for 6 years and it started this only over the past winter. In the past during the warm months it started and idled down immediately.

 

[Mounce]

When's the last time you cleaned the throttle body and reset the PCM?

 

[littleblazer]

Just to add to the post above me, you replace the battery recently or have it go dead?

 

[coolasice]

No offense, but I disagree. I've had the truck for 6 years and it started this only over the past winter. In the past during the warm months it started and idled down immediately.

got a scantool? check coolant temp when cold and after warmed up. (clean maf and throttlebody and reset pcm)

 

[Black08TB]

Just to add to the post above me, you replace the battery recently or have it go dead?

Never wen't dead, but replaced the original battery last fall when I did ball joints, wheel bearings, transfer case oil and spark plugs.

I cleaned out the throttle body when I changed the spark plugs with spray carb cleaner. No on the MAF. The 4.2 was running fine.

I've never had a real fuel injection service performed at a shop, I do add a can of Seafoam to a tank of fuel 3 or 4 times a year and use Mobil gasoline almost exclusively.

Had the coolant flushed and thermostat replaced in March this year.

How would I go about resetting the PCM?

106K on the truck, just in case it matters.

 

[coolasice]

Never wen't dead, but replaced the original battery last fall when I did ball joints, wheel bearings, transfer case oil and spark plugs.

I cleaned out the throttle body when I changed the spark plugs with spray carb cleaner. No on the MAF. The 4.2 was running fine.

I've never had a real fuel injection service performed at a shop, I do add a can of Seafoam to a tank of fuel 3 or 4 times a year and use Mobil gasoline almost exclusively.

Had the coolant flushed and thermostat replaced in March this year.

How would I go about resetting the PCM?

106K on the truck, just in case it matters.

pcm reset
http://gmtnation.com/forums/topic/8296-throttle-body-tb-relearn-42/#entry172547

 

[Black08TB]

Thanks Cool, I'll give that a shot this weekend!

I need to change a heat blend door actuator (I bought a GM one a few weeks back) on the driver side and I'll do the PCM reset while I'm at it.

 

[Mounce]

Gotta clean the TB when you reset the PCM...if not, you'll have a bad time.

 

[Black08TB]

Will do!