Shuts off, idles, revs and accelerates itself

AKEVANS

MEMBER
2003 BUICK PARK AVENUE
AUTOMATIC
203,000 MILES

My car when turned on will idle sometime but also rev itself then go back to running like normal the rev again. It does this with driving too and it accelerates on its own then stops accelerating on its own. It will also shut off after driving a few feet or drive completely normal. The mass air flow has been replaced with another Buick part not from the same model but a compatible model. It's a second hand one though.

1 Reply

AL514

MECHANIC
4,632 POSTS

Hello, it sounds like you have a vacuum leak, possibly at the intake manifold gasket. I have had other cars do this same exact thing. They almost seem to drive themselves. This is because the engine computer is reacting to "false air" getting into the engine. It will open and close the Idle Control Valve trying to compensate for the issue but it can't, so it just goes back and forth. The engine computer also sees extra oxygen in the exhaust from the oxygen sensor data and this causes the fuel control to do the same thing, switching back and forth between different fuel injection measurements. I'll put a guide below to help with vacuum leaks. The best way to find leaks is to use a smoke machine to fill the intake with smoke with the system sealed off. When slightly pressurized, smoke will come out any leaking areas. Try block off the Brake Booster Hose as well, just to verify there's no leak through the Booster. But it sounds more like an Intake Manifold leak.

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

https://www.2carpros.com/articles/mass-air-flow-service

https://www.2carpros.com/articles/engine-idles-too-high