I posted about this a while back...but noone really knew for sure...It may be a general/engine question..but My car is a TBI, so, that's why I'm posting it here.
When the car's in gear but stopped (at a light)with foot on the brake, the gas will surge a little,...then go back down.
It does it till' I start going again. Not a big surge where it's dangerous...but it has scared Me a little sometimes. If I don't have a firm grip on the brake I could lurch forward, some. BUT....
It didn't happen all summer...and the last time I remember it happening was last winter. So, I guess this is something that gets worse in the winter (look at Me, I'm a friggin' genious!)
Has anybody ever heard of this?
it's a 91' RS TBI 305 auto with an open element K&N, if that helps...
Thanks for any info!

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Everything I know I learned by messing it up at least once.

 

Mine surges a little but not the point you say. Um obviously check the vaccum lines, make sure your plug wires are all connected. Your car will run surprisely well on 7 cylinders. And maybe even see if you need to put some more or less timing when it's cold. I may think a few more (probably not it) ideas.