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Q: Violent surging from rough idle after cleaning throttle body and putting in gas

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The van has stalled 2x when stopped at a light, seems to coincide with letting my foot off the break. It starts again just fine. Also stalled when breaking in a parking lot and in a gas station. After cleaning throttle body and the iac valve, the van seemed to have a smoother idle. I noticed the van didn't have a throttle body cover or a gasket between the IAC motor and the intake passage. I placed a gasket b/w the IAC motor and the intake passage but still no gasket cover. Anyway, gas was on E. I put 1 gal. in the tank, the van sounded the same, and I noticed white emissions for the 1st time. Later, I filled the tank to 3/4 full, then stalled in the station. I then stalled at a stoplight. Later, in my driveway, with my foot on the break, the van's surges were the worst I've heard and felt. Each surge moved the van forward as if being pushed from behind while in park and in drive. I'm afraid to drive it. Any help is MUCH appreciated!!!

My car has 177000 miles.
My car has an automatic transmission.

Hello and thank you for contacting YourMechanic. You may want to perform a tune-up and change all of the spark plugs and wires first. Then check for vacuum leaks on the engine with a vacuum gauge. If the vacuum gauge reads less than 15 hg, then look for any vacuum hoses that may be disconnected or cracked.

A vacuum leak will stall out the engine and cause a rough idle. If you need assistance with finding a vacuum leak, then seek out a technician, such as one from YourMechanic, that can diagnose your rough idle and assist you with fixing your vehicle.

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