Idle issue after getting truck back from mechanic

[Fourtyfive]

2007 Silverado 1500 classic 5.3 flex.

Truck starts up fine when cold, but as it warms up, the idle gets a little choppy. When starting after warm, the rpms drop down below 500 then go back up, bouncing a little before leveling out. Wondering if this could be TPS or throttle body related. No check engine light and truck performs fine other than idle. 

 

The exhaust has a pretty bad smell to it as well, especially after I get on it. Not sure if these are related.

[Black02Silverado]

What did the mechanic do?

 

Check your MAS and TPS connections.

[Fourtyfive]

1 hour ago, Black02Silverado said:

What did the mechanic do?

 

Check your MAS and TPS connections.

Had the truck in to get brake booster and master cylinder replaced. Noticed the idle when i went to pick it up. He looked at it and said he thinks the throttle body might be going out, drive it for a week and see if it will fix itself. Well it didnt and he didnt sound vary confident in his diagnosis. 

 

Just wanted to check to see if anyone had this issue and/or could help narrow it down.

 

The connections appear to be fine. Cleaned out the throttle body and it the idle seems to have smoothed out a little, but still bounces when starting after the trucks warm. 

[Black02Silverado]

2 hours ago, Fourtyfive said:

Had the truck in to get brake booster and master cylinder replaced. Noticed the idle when i went to pick it up. He looked at it and said he thinks the throttle body might be going out, drive it for a week and see if it will fix itself. Well it didnt and he didnt sound vary confident in his diagnosis. 

 

Just wanted to check to see if anyone had this issue and/or could help narrow it down.

 

The connections appear to be fine. Cleaned out the throttle body and it the idle seems to have smoothed out a little, but still bounces when starting after the trucks warm. 

OK sounds like a vacuum leak.  Check all the connections around the brake system.

[Fourtyfive]

50 minutes ago, Black02Silverado said:

OK sounds like a vacuum leak.  Check all the connections around the brake system.

Just checked the connections. Only one hose coming off the brake booster itself. Hose is in good shape, no cracks that i could see. The barb its connected to does rotate freely on both ends. No idea if thats normal. Checked the rest of the vacuum lines around the intake, all appear in good shape. 

[mjm-1957]

Pull the master cylinder away from the booster and make sure the O-ring is there on the end of the master cylinder.

[Fourtyfive]

Yes the o ring is on master cylinder

[Cammedsilveradodude]

What kind of smell out the exhaust? Eye burning like raw fuel? Or fireworks smell? If you can go to a parts store and scan it, maf grams should be at 4.5-5.5 at idle warm and such. Gm relies on maf for a lot. Sounds like your truck is staying in open loop or vacuum leak. 

[carkhz316]

Can you find out if they disconnected the battery during service? I know it shouldn't be necessary for the MC and booster repair, but since everything in the book says to disconnect the battery to be safe, it could happen. If this happened, and your throttle body was a bit dirty, it will go through an idle relearn that can take a few hours, to a couple days of normal driving to complete. This correlates a bit with you cleaning the TB to improve it. Just drive it for a few days and report back before you start digging into it.

[Fourtyfive]

34 minutes ago, carkhz316 said:

Can you find out if they disconnected the battery during service? I know it shouldn't be necessary for the MC and booster repair, but since everything in the book says to disconnect the battery to be safe, it could happen. If this happened, and your throttle body was a bit dirty, it will go through an idle relearn that can take a few hours, to a couple days of normal driving to complete. This correlates a bit with you cleaning the TB to improve it. Just drive it for a few days and report back before you start digging into it.

Got the issue fixed. It was a relearning issue but had to get the ECU reprogrammed for it. Had been driving it over a month and it didnt relearn on its own. Chevy dealership checked it out, reset the ecu and no more idle issue.