Sometimes van engine revs and then All trans gears slam

As above Recently car backed into my 2006 Chevy Van. Shortly thereafter, engine. Sometimes revved high and ALL gears started slamming. When idling normally van shifts normally . Since it’s all gears involved with high idle I"m thinking computer info problem engine communication to tranny. Any ideas?

Putting the van in gear while the engine is revving too high will cause slamming. Keep doing this and you will end up with damage to the transmission and other driveline components. You need to fix the revving problem. It could be a sticking throttle, a vacuum leak, or some other problem. Is the Check Engine light on?

Thanks for responding. No check engine light. First can I lower the idle speed? Please remember at this time the idle is usually fine/smooth gear change. Will the attempted cure be worse than. The disease?

Idle speed is controlled by the engine computer. What is needed is a systematic diagnosis to determine why the computer is getting it wrong. How bad was the damage from the rear end hit? Perhaps an emissions fitting at the gas tank was dislodged or damaged.

If the attempted cure begins with an accurate diagnosis, no harm done.

Was there not an insurance claim involved . If there was then contact the other persons insurance and inform them you still have unresolved problems.

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A good collision center should be able to address the problems. Involve your insurance too, they may be able to help you deal with the other company. Hopefully you have a report from a law enforcement officer.