[agb1758]

Anybody have any idea what would cause a engine surge on decline? Got a 98 Grand Am I'm working on, when I go downhill, only after first starting it, it will rev up about 500 rpm's, won't do it when warm. Checked motor mounts, and binding in accelerater cable, all good. Computer diagnostics show no problem. Real pain!!!

[HotRodF100]

This may be way off but.... I had 3.1 and a 3.8 that did kinda the same thing. On the top of the engine there is an idle mixture motor, it is just before the the throttle plate. It has 2 torx screws in it and a weatherproof connector. When you remove the motor, it had an O ring seal, a shaft sticking out with a spring around it, and a cone-shaped end that is about 1/2". My symptoms were mostly after a stop behind a vehicle, the engine would drop to a low RPM, then rev up and you feel like you would hit the guy in front of you. Remove the motor and clean the plunger and shaft as well as the surface that it closes off against inside the intake. It will be black with gook, brake cleaner works well for cleaning it off. You can pull the shaft out or push it in but if you do, it take about 25 miles before the computer gets it back to the right place. In those 25 miles, the idle will be all messed up. Even if this doesn't fix it, it's a good PM measure anyway. To replace the motor I'm told is about $80. Hope this helps, Good Luck!!