Jeep runs bad until I stop, then fine from then on

My 1999 Jeep Cherokee, 4L inline 6, has a very weird problem. Usually, after starting, it runs well for around 10 seconds, during which time I back up and get ready to leave. Then when I switch to drive, it starts to run poorly, having no acceleration in speed or and very little in engine rpm, until I stop using the brakes. Exactly when the suspension relaxes, the idle returns to normal and it runs perfectly after that.

Sometimes the rough running starts while I’m backing up too. So I don’t think it related to the transmission. But all I have to do is completely stop, and then it runs great from then on.

This doesn’t happen every time, but probably 60-80% of the time. It’s been happening for about 2 months now. Thanks in advance for your help!

The brake booster check valve may be causing your problem.

Has the ‘Check Engine’ light come on at all?

No, the Check Engine light has not come on at all. Rod Knox - How would the brake booster check valve do this?
Thanks for the help!

A vacuum leak will cause the engine to lose power and run poorly. Along with the possibility of a faulty check valve, a weak driver side motor mount can cause the engine to lift toward the passenger side when accelerating in a forward gear and pull the vacuum connection at the booster.

Thanks! I’ll check both.