Hello new here. Sorry for the long post anyways. All GM factory parts used / Fel Pro gaskets

i have a 2008 Tahoe with DOD. I had a small oil leak coming from the valley cover so I took off the manifold to replace while replacing I also replaced the manifold gaskets and oil pressure sensor.

Well I put everything back together and now I’m having a surging issue (400-800rpm bouncing) with any load on the motor (AC, power steering, brakes) only notable when sitting in park the truck will just keep surging up and down until the ac is shut off.

so far I have eliminated the following:
vacuum leaks
battery is new
alternator tested (13.25) with load
replaced throttle body (gm part)
had throttle body zeroed in.
All grounds look ok.
MAF is clean.

im at an absolute loss what could be causing this annoying surge that only happens when vehicle is in park with load on motor. Didn’t have this issue before I replaced the valley cover/ manifold gaskets.

How did you do the throttle body?

had shop program it

Hoping to get some ideas of some things I might not be thinking of or overlooked.

I think you have a vacuum leak.

I thought so too vacuum leak is not the issue.

For grinns you can try to disconnect the battery and touch the battery cables together for a few seconds and reconnect and see what happens.Some times a Global reset can help. If not, Can you see what your fuel trims are?

Fuel trims are as below:
shortft1: -3.6
Longft1: -5.5
shortft2: -3.6
longft2: -5.5

FRP: 50psi


those are averages as number were fluctuating