Cleaned throttle body. Now high idle.

nospark

Original poster
Member
Feb 20, 2012
28
Hazelwood MO
Hello, I just removed TB and gave it a good cleaning. I disconnected battery first as I thought it cleared computer. Now I have idle of about 2500rpm. If I put it in gear it simmers down to normal in a few moments and then shift to park and it stays normal. Hit the throttle and it goes back to high idle again. Never had this problem with 04 Trailblazer. Now I have 07 Tahoe with 5.3. Please help and Thank You
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
Have you driven around for a half hour or so in stop and go traffic to allow the computer to relearn the new behavior of the throttle body?
 

Hypnotoad

Member
Dec 5, 2011
1,584
It sounds like you may have a vacuum line that you forgot to hook back up or accidentally disconnected in the process.
 

Envoy_04

Member
Jul 1, 2013
749
Hypnotoad said:
It sounds like you may have a vacuum line that you forgot to hook back up or accidentally disconnected in the process.

I agree, this is easy to do and not even think about it too. :yes:

I once bolted my throttle body back on, turned to do something else, and came back and hooked up the air intake piping picked up my tools and shut the hood. When I started it up it was running all kinds of rough, it would almost die, then rev, and repeat. Wouldn't respond at all to the throttle. Took me a minute or so to realize I hadn't hooked the vacuum line OR the wiring connector back up. :rotfl:
 

nospark

Original poster
Member
Feb 20, 2012
28
Hazelwood MO
Update. I agree that vacuum line could have same result and I have checked the 1 that I was a where of that comes off the 'blob' duct work that's hidden under top cover. Sort of looks like small 90' pcv valve and connects to steel line. Rechecked wiring ect. I took it on a mostly highway run about 28 mile round trip and that helped slightly. When I got back I checked this thread before having to run again. Going off of Roadie's reply I took regular streets instead of highway. It got better with every complete stop I had to make. Never hoped for red lights before. It seems to be relearning with each stop and the performance is coming back. It was running rather flat from a rolling get in it hard scenario. I assumed disconnecting battery would reset to factory defaults. That work with the I-6 Trailblazer I had witch I figured out the 1st time I cleaned it's tb and didn't follow step #1. Disconnect battery. Had similar issue then with idle would spike last second when stopping. I believe Roadie cought me on that error. Other than knowing this issue yesterday was just not right, my daughter was driving Tahoe to work night shift. That bothered me more than if I was the only driver. I will be checking back with this thread hoping someone know's a way to prevent this idle issue when cleaning tb and 'sticky' it as it needs to be known. Its stupid. This could bad results for inexperienced driver and/or just piss off experienced DIYer. Thank you all. And yes, interruptions can cause mistakes, glad I proofread this.
 

IllogicTC

Member
Dec 30, 2013
3,452
nospark said:
Update. I agree that vacuum line could have same result and I have checked the 1 that I was a where of that comes off the 'blob' duct work that's hidden under top cover. Sort of looks like small 90' pcv valve and connects to steel line. Rechecked wiring ect. I took it on a mostly highway run about 28 mile round trip and that helped slightly. When I got back I checked this thread before having to run again. Going off of Roadie's reply I took regular streets instead of highway. It got better with every complete stop I had to make. Never hoped for red lights before. It seems to be relearning with each stop and the performance is coming back. It was running rather flat from a rolling get in it hard scenario. I assumed disconnecting battery would reset to factory defaults. That work with the I-6 Trailblazer I had witch I figured out the 1st time I cleaned it's tb and didn't follow step #1. Disconnect battery. Had similar issue then with idle would spike last second when stopping. I believe Roadie cought me on that error. Other than knowing this issue yesterday was just not right, my daughter was driving Tahoe to work night shift. That bothered me more than if I was the only driver. I will be checking back with this thread hoping someone know's a way to prevent this idle issue when cleaning tb and 'sticky' it as it needs to be known. Its stupid. This could bad results for inexperienced driver and/or just piss off experienced DIYer. Thank you all. And yes, interruptions can cause mistakes, glad I proofread this.

There is no way to prevent it completely. The PCM is literally "sniffing out" the precise calibration of your throttle body. Same thing is done for transmission adaptive shift points, transfer case adapt ready points for A4WD, even the CASE relearn. Sometimes, you'll have like I had - it just idled a bit high for about three minutes and simmered down, followed up with some driving and all was completely fine. Others may experience what you had.
 

HARDTRAILZ

Moderator
Nov 18, 2011
49,665
I have had an idle of about 1000 rpm at every cold start for a couple months. Unhooked the battery a couple times with no change.

After some driving it goes down to the normal 600 or so rpm, but it is rather annoying that this happens.
 

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