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Gas Pedal Vibration during Accelleration post Engine Work

Looking to query the collective knowledge of this forum for an issue that I haven’t been able to have answered. The car is a 2000 Pontiac Grand Am, 3.4 L V6, 223K miles.

I had a major coolant leak and my normal repair shop couldn’t handle it due to lack of equipment. So to a local dealership I went. The following is the assessment and work performed.

“Cylinder head gasket leaking coolant. 12.80 Pressure tested coolant system and found the rear bank cylinder head gasket leaking coolant down the front of the engine. Replaced both head gaskets as well as intake, front engine cover gasket, valve cover gaskets and upper plenum gasket required for repair. Topped with coolant and performed LOF. Cleaned engine compartment area and road tested. Verified condition corrected”.

When driving the car off the lot after the repair, I nearly stopped and went back in to complain. The gas pedal was vibrating on acceleration and its never done that before. I figured I’d drive it around for a while and see if it shook out and it didn’t. I did drive back to the dealer the same day and rode with the mechanic who agreed that the vibration is there but didn’t realize it was new. He went step by step through the repair with me. All work was done from the top of the engine down so the transmission and CV joints were never touched. The only idea the mechanic had was there is a small crack in the shielding on the throttle cable along with rust. I’m tempted to replace this anyways from a safety standpoint but could this cracked housing/rusted cable be causing the vibration? During the course of the repair, this is the only part that was touched that is related to the throttle. The throttle itself is fine.

The vibration only occurs when accelerating from a complete stop. It evens out once a speed over 40 mph is reached. It does not seem to be dependent on the AC compressor running.

Any ideas/suggestions are most welcome. Thanks!

After the intake manifold was replaced on my 2000 Blazer there was a buzzing/vibration under acceleration. I traced it to the accelerator pedal. The throttle cable had not been secured to all the tie down points under the hood. I tied it down with a few zip ties to fix the problem.

Ed B.

My wild guess is that when they changed the headgaskets they didn’t properly adjust the valve lash. That would show up as a nervous vacuum gage needle.

What I`m thinking is that since the only connection from the gas pedal to the engine is the throttle cable that the vibration must be coming through the cable.I think they might have twisted or turned the end of the throttle cable to get it to line up with the throttle body linkage when they reconnected it causing the cable to have torque in it like a wound up spring.
I would disconnect the throttle cable from the throttle body and extend it out as straight as you can.If the cable is turned or twisted inside the shielding, straightening it out before reconnecting it should allow the cable to untwist/untorque itself inside the shielding.

I definitely think the vibration is being caused by the throttle cable whether it wasn`t routed correctly, not tied down correctly or twisted inside the shielding.