'07 Suburban: post-TB clean idle woes

[Alex_V]

A friend's '07 Suburban (5.3, 184K) threw P0121 yesterday. Another friend who's plenty capable with all things post-2000 Chevy trucks scanned it, cleared the code, and sent him to me to clean the throttle body.

No CEL when I got it, no strange behavior as I pulled it into the shop. Took the throttle body off the intake but left it plugged in (caught the carb. cleaner and goo in a container) thinking that would avoid having to re-learn the throttle body. Upon startup, idle jumps to 1,700 but doesn't immediately come back down, instead staying right there, then slowly climbing up toward 2,500. Plugged in the scanner to watch the data, played with it for a minute, then took it for 6-mile drive. Runs fine, settles down to idle when in gear, and doesn't jump up high when moved from drive or reverse back to park. However, just like clockwork, when I tap the gas pedal in park the idle jumps up again and doesn't come back down until I put it in gear again. Also, startup idle is still just as high. Data shows desired idle @ 650-700 and actual at whatever speed it's revving, most of the time being ~2,400. Just to check it off the list I pulled the connectors on the TB and gas pedal sensor, inspected and applied dielectric grease - no change. Still no CEL, either.

Any wisdom?

 

[mclasser]

Does the service manual specify an idle relearn procedure?

 

[Ethan1]

Sounds like you need to relearn the idle with a bidirectional scantool.

 

[WobblyElvis]

I have heard of this but never experienced it myself.

1.Disconnect the battery and hold the + and - leads together for a few seconds.
or
2.Simply give it more time

I am sure you do not need any special toolsl
Hope you didn't over apply any cleaner to the throttle body. You don't want cleaner in the motor/gears

 

[Alex_V]

The guy that pulled the codes said he's sure it just needs relearned. He needed it this evening but it'll be back tomorrow for rear brakes so I'll do a proper re-learn then if it hasn't straightened itself out.

 

[GenesisGuy70]

I know it's not a Ford but I've done this a few times and I know it does what he says it does because I've done it.

https://www.youtube.com/watch?v=hZAsoqmqhdM

 

[Merkava_4]

Originally Posted By: Alex_V
Any wisdom?


Yes. It helps if you remove all the sensors from the throttle body before you start cleaning it. GM uses a Tamperproof T20.

 

[yugrus]

You should never open the throttle plate by hand if you don't have the scanner to follow the re-learn procedure. It is easier to have an assistant to open the plate by stepping on the pedal with key on, engine off, while TB is still on the car. This way you can clean the front, then remove the TB and clean the back. Get the shaft area good, so it doesn't stick. Clean as much of the intake as you can get, while there.
If the shaft isn't sticking, the idle will come down with time. Disconnecting the battery is another option, as previously suggested.

 

[TmanP]

My GM has a procedure to relearn the idle (after the battery is disconnected). I don't have the repair manual on me but it's so many seconds with the key on but the engine off, so many seconds with the engine running, then shut off.

I'd look for a similar procedure online, disconnect the battery and try again.

 

[LeakySeals]

Sounds like the TPS. i replaced my TB a couple years ago for something similar. They are relatively cheap to shotgun if you want to Hitachi TB W/TPS

Clearing codes is fools gold. Doesn't fix the problem, doesn't make it go away. Makes it harder to fix a problem. Most codes will clear on their own when fixed. A relearn procedure should not be necessary if the engine is running good. When you reset power, it resets to factory original config. Should not be any noticeable changes if things are good. Learning is continuous and ongoing. So there is no point.

 

[GMBoy]

Here is the relearn procedure you HAVE to do and with a Tech2 or similar high end scan tool:


Scan Tool Idle Learn or Idle Learn Reset Procedure – Performed after the throttle body is cleaned or replaced
1. Ignition ON, engine OFF, perform the Idle Learn or Idle Learn Reset in Configuration/Reset or Module Setup.
2. Engine idling, observe the scan tool Throttle Body (TB) Idle Airflow Compensation parameter. The TB Idle Airflow Compensation value should equal 0% and the engine should be idling at a normal idle speed.
3. Clear the DTCs and return to the diagnostic that referred you here.