Bad Throttlebody assembly?

[GangstaCowboy]

Hello-
Over the last few months I have been trying to track down some vibrations and sound in the engine bay. Currently the symptoms are when idling cold and in reverse the engines will shake making noise in the cabin. The shaking also occurs when the heat or ac is on, regardless of fan speed. Sometimes if I press the brake peddle hard enough the engine rpm will drop extremely low almost like it wants to stall. One occasion the engine died on me while I was parked, but never happened since. I initially thought a TB cleaning would help and it seemed too a little. If revved the car up in park and took my foot off the gas the idle would dip and all the lights would dim for a second and then it would come back up to normal. After the TB cleaning this went away but the other symptoms remain. Has 139k miles on it and new plugs and wires since 110K. Could the TB assembly be bad and the extra load on the engine from the AC system, brakes, or transmission be causing this? Other than this the car drives perfect but I can tell something is going on. One small note when I cleaned the TB the butterfly valve some to stick a little when almost closed. Is that normal?

 

[OR VietVet]

Care to share the year and model?

 

[GangstaCowboy]

That would be helpful. 2006 Tahoe

 

[OR VietVet]

You can try and get MAF cleaner at the parts store and follow directions and be prepared for higher than normal idle for about 1-2 days till it relearns. I personally think you may have a couple of problems going on. You may have the dreaded intake manifold leak causing a vacuum leak. When you do this check you can use a spray bottle of water and spray around the intake mount area and see if the idle changes. Keep in mind the MAF cleaning may fix all problems. The sticking throttle plate may just be more gunk at the pivot at the bushings where rod goes thru. spray the cleaner right on there and wipe away with clean rag.

If you do the intake gaskets do this: Use only Felpro gasket kit, new bolts/nuts where it is bolted down, make sure everything is extremely clean on reassembly, replace the knock sensors with AC Delco and do the knock sensor harnesses with AC Delco or Dorman and look at you tube for tips. This is a common problem/leak after 100k.

 

[GangstaCowboy]

Thanks for the advice, I will check the gasket for leaks. Sometimes I hear the vacuum pump running when nothing is on. Is that a sign of a leak somewhere? **Edit: I meant to add I have thoroughly cleaned the MAF and no change in symptoms.

 

[OR VietVet]

Where do you have a vacuum pump?