Errattic idle

I am getting fluctuating idle either in park or in Drive(stopped). RPMs jump up and down from 500-900 for about 5 secs then idles fine for a few then jumps up and down again. I get no CEL or codes. I did clean the throttle body out (battery disconnected) and ran fine after that. All intake hoses/lines are reconnected and the 2 wire connectors are attached. any ideas?

It does sounds like a vacum leak somewhere on the engine. The easyest way to find out is to start the trailblazer and let it idle. Take a can of carb. cleaner and spray it around vacum hoses and the where the gaskets are on the throttle body and intake to see if there are any leaks.

If there is a leak the carb. cleaner will instantly make the idle of the engine jump up due to more gas being placed into the system. I have found that this is the fastest and easyest way to find vacum leaks.

i did clean the throttle body so maybe somehow a line came loose that i didnt catch. i will thy that, thanks for the tip.

Well i basically removed everything as i would be doing a throttlebody cleaning. disconnected the battery, removed the intake resonator and TB. all vac lines/hoses were intact. reinstalled everything and started her up and no bad idle. We'll see what happens when the wife drives it to work.

Well i basically removed everything as i would be doing a throttlebody cleaning. disconnected the battery, removed the intake resonator and TB. all vac lines/hoses were intact. reinstalled everything and started her up and no bad idle. We'll see what happens when the wife drives it to work.


Ok well keep us posted like to know that we done somthing right.

When disconnectiung the battery the pcm has to go thru a idle relearn, disconnecting the battery is not required to clean the tb.

When disconnectiung the battery the pcm has to go thru a idle relearn, disconnecting the battery is not required to clean the tb.

but you want to disconnect the battery so the pcm has to relearn the idle since the TB is now clean.

Still unecessary, this will happen without the battery disconnect.

Still unecessary, this will happen without the battery disconnect.
ok well i thought that was norm. learned something today.:grinyes:

well its doing it again but not as bad. going between 500-900 rpms and you can tell its affecting the headlights.

At this point if no obvious vacuum leaks, a full scan is in order.

At this point if no obvious vacuum leaks, a full scan is in order.

from a TechII? or would those SnapOn tools work also?

whats the function or what function is provided by the 2wire connector that attaches to the alt?

Snap on scanner is ok.

well since i resoldered that red wire it hasnt done it. its been 3-4 days now.

What red wire?

the red wire that goes to the connector that connects to the alt.

No mention of this issue in your previous posts, could have made some suggestions had we known. Broken, corroded? This is a control wire from the pcm that helps vary alt output.

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