I have been around cars my whole life and do all my own work, but I am at a total loss with this problem. Here's what I have a 2007 trailblazer SS it has a 408 in it with a PRC L92 top end with truck intake, comp cam 227/238 114 and kooks 1 7/8" headers and magnaflow full exhaust, RPM level 5 trans with a Yank 3600 converter. A week ago I removed the throttle body to clean it and replace my air filter on my cold air intake. Ever since I did this my idle has been crazy. When I start it cold it jumps up to about 3500 rpm then slowly idles down to its normal 800rpm. When in gear it surges BAD and is worse the lower the gear your in and even worse with the A/C on. I have checked for vacuum leaks even had it smoked and it has been a week and about 300 miles so any relearning should be done ? I have noticed lately when you first start it the engine pops and sounds like its skipping for about the first 10-15 seconds then smooths out. I have also noticed my gas mileage has gone in the toilet about 5-6 MPG and feels down on power. Would a bad 02 sensor cause this ? or would that throw a code because I have no codes and I have scanned it multiple times. I am starting to think I damaged something in the throttle body electronics with the cleaner, but would that cause these symptoms ? or maybe its something completely different that just happened the mess up at the same time ? I tried the trailblazer site and all I got was insults how I'm stupid and if I was a good mechanic I would know the problem ? I feel everyone has a time when they need a second set of brains or a fresh set of eyes on the problem.

 

sounds like a vacuum leak or maybe you hosed the maf somehow? But you said you had it smoked.. no leaks found I'm guessing

 

How did you CLEAN the throttle body? Agree this sounds like something related to whatever you did during the cleaning process, inadvertantely of course.

Jon
PSI

 

Did you perform an idle relearn procedure? Also make sure throttle blade isn't binding closed when shut.

 

the first thing I did was an idle relearn I found online for the LS2 trailblazer and it didnt work, I then took it to the dealer so they code force a relearn with the Tech 2 that did not work so a couple days later I had it smoked and they fond nothing after doing 3 times ?

to clean it I took off the throttle body and sprayed it with brake parts cleaner and wiped it down and then sprayed it off with more brake parts cleaner ? I did notice the black plastic is discolored now looks grey ?

It will idle down just very slowly and sometimes slower than others ? i have also noticed if I run WOT for any length of time and let off it will be stuck at 2000 rpm for about 30 seconds and then drops to 1500 and will not go below 1500 till I come to a complete stop and wait about a minute then it will finally kick down to 800 rpm ?

I just bought a new throttle body ? i have found numerous posts like this but they are just a high idle and most just stop after a couple post never saying the cause ?

 

wanted to also say thank you for the help so far

 

Do you think the brake clean got into the circuitry inside the throttle body. I only ask because Brake Clean and Throttle Body Cleaner are different. I know brake clean is the universal cleaner for most of us, but it can do some nasty things in the incorrect application. Could be why the plastic discolored. Dont want to point you in the wrong direction but being that you have that black cover over the throttle body (where the 6 pin plug goes) it isnt hard to imagine something getting in there to the circuit board. Just a thought.

Lastly, could the TECH II force the idle down? Are there any codes being set?


Jon
PSI

 

Sounds like your maf took a **** on you for whatever reason....

 

That's what I was thinking that the brake clean damaged the circuit board ? I will know today the new throttle body should be here ?

 

we will find out today I have a friend coming over with a MAF too in case the new throttle body don't work.

 

eliminated the MAF today we switched it out and the same thing still, of course Fedex rerouted my throttle body so now it has taken 3 days longer than expected ? maybe tomorrow it will show up ?

 

just out of curiousity, it the throttle body ported? ive seen a friends act like that when he ported his and went to close to the butterfly... possibly gunk had build up and help seal it and once cleaned it cant seal. no dbw seals perfectly as the blades do not touch the edges of the housing... just a thought... after i ported mine it would idle at 1500 for about 2 seconds after i stopped, then down to 975, where i have mine idle, then its normal

 

no porting, I was thinkin of getting one glad I didn't now it would idle at 3,000 rpm LOL still no throttle body I think Fedex just does what they want my scheduled delivery has changed 3 times ?

 

Sounds like the brake clean screwed up the throttle body. I've only used Throttle body cleaner myself, or just some simple green and let it soak on the backside of the blade. I've also heard about the TBSS being kinda tempermental when it came to cold air intakes, like you HAVE to get a tune kinda tempermental.

 

I made a similar mistake on a friends saturn with dbw tb. It ruined the circuitry inside. It was hard to figure out since I thought cleaning it would help. My bet is the tb is bad.

Someone correct me if I am wrong but a simple test to eliminate a maf (I know you already swapped it) by unplugging it. The vehicle goes into open loop. If the maf is the problem you would be able to notice a change in how it runs once it's unplugged.

 

You are correct on the MAF, as I'm sure his has an integral IAT sensor also.

 

I think it was the brake clean still waiting for the new TB to come in ? I have had this tune since the engine install and never had an issue till now I don't think the cold air intake would cause a problem now it has one on there in one form or another since the 408 has been in it. I'm really leaning towards the TB being messed up ?

 

Agreed. Post when you get the new throttle body. Good information.

Jon
PSI

 

just installed new throttle body and it runs like new again, thank goodness. I was getting nervous every person i talked to had a horror story about the PCM or tune changed or something....put the new on on and it runs great perfect idle again no popping. Thanks for all the replies and hope this helps someone else with a similar problem. Moral of the story "DON'T USE BRAKE CLEAN ON A DBW THROTTLE BODY !!"

 

I did this once. Its the TPS. They're about $34 to replace. When you clean a throttle body all the sensors need to come off too. Moisture will seep through the butter fly bearing and will ruin the sensor after about 2 days. I see you might have bought a whole new TB.. Sorry man but it was only a TPS