High Idle, Low Idle, Unintended Acceleration, Rough Downshift, Clean Throttle Body

[ChicagoSSV]

Hey all,

I got a fairly common base issue but it seems unique- I had a slight idle rev (200rpm) on the first start only, warm/medium ambient temp outside. I got bored one day, cleaned the throttle body which was a bit dirty but fair for 120K miles. I forgot to disconnect the battery before pulling the TB connector though. I did move the blade but slowly and smoothly. After re-install, idle was same, car drove fine. I did the 3min on, 3min off and drove the car (in tow mode as I do) it was all the same, no improvement. Next day, high idle, about 2,000 rpm for maybe 5s, and the car drives like garbage. Rough downshifts, unintended acceleration, high idle on random starts, realllly low idle in gear but smoother than any other sub-500 rpm idle Ive ever heard of. I cant even hear the exhaust at stop lights, passengers think the car died..It drives worse in regular vs tow mode, almost dies on downshifts in regular with no shudder or anything but I can see the tach. dip down low. I tried a fresh TB and some highway miles but its been a couple months, I need help. No codes, 2013 Tahoe SSV. Please let me know what you think.

Thank you

 

[Fless]

Might scan your long- and short-term fuel trims to see if they indicate anything.

 

[Foggy]

There is a TB clean procedure that you can do with some scan tools..
It resets the "learned" zero position as that has most likely changed in 120K miles...
Also, check/remove/ clean your connector to the TB and MAF sensor.
If the Key is Off , you don't have to disconnect the battery

 

[Doubeleive]

I would be giving the MAF a hard stare.....all your weird problems can be pointed right at it. just food for thought don't run out and buy one but I would be watching it on the scanner for sure. Could be the TB didn't want to be cleaned..... I clean mine every 3 months so it's used to getting it's @ss wiped

 

[Doubeleive]

I would also go back and spray some cleaner in the TB harness both sides, let dry and reconnect.

 

[swathdiver]

Hey all,

I got a fairly common base issue but it seems unique- I had a slight idle rev (200rpm) on the first start only, warm/medium ambient temp outside. I got bored one day, cleaned the throttle body which was a bit dirty but fair for 120K miles. I forgot to disconnect the battery before pulling the TB connector though. I did move the blade but slowly and smoothly. After re-install, idle was same, car drove fine. I did the 3min on, 3min off and drove the car (in tow mode as I do) it was all the same, no improvement. Next day, high idle, about 2,000 rpm for maybe 5s, and the car drives like garbage. Rough downshifts, unintended acceleration, high idle on random starts, realllly low idle in gear but smoother than any other sub-500 rpm idle Ive ever heard of. I cant even hear the exhaust at stop lights, passengers think the car died..It drives worse in regular vs tow mode, almost dies on downshifts in regular with no shudder or anything but I can see the tach. dip down low. I tried a fresh TB and some highway miles but its been a couple months, I need help. No codes, 2013 Tahoe SSV. Please let me know what you think.

Thank you

Sometimes the computer will raise the idle to provide a little more power to the alternator to charge the battery. Most folks don't notice it.

Look for vacuum leaks or something you forgot to re connect. If you took the throttle body off the intake, make sure you didn't pinch the gasket (o-ring).

 

[iamdub]

Sometimes the computer will raise the idle to provide a little more power to the alternator to charge the battery. Most folks don't notice it.

Look for vacuum leaks or something you forgot to re connect. If you took the throttle body off the intake, make sure you didn't pinch the gasket (o-ring).

^This.

I was gonna say to recheck everything you touched to see if you didn't properly reinstall something and now have a leak after the MAF. It's too easy to fold the lip on the coupling where the intake duct meets the throttle body. This is often done on the underside so you don't see it. The factory coupling is a tight fit so I squirt a shot of lube on it and smear it with my finger so it's just a really light coat. Makes a world of difference.