I've tried searching for an answer, but to no avail, so here goes. I have an 88 GXL, and I just got a new exhaust installed recently. Over the past couple weeks, my car has been shuddering while letting the car coast in gear. I replaced the spark plugs, and installed the correct ones after seeing that my old mechanic installed the wrong type and didn't tighten them in the spark plug holes at all......... so i had a lot of black sludge on the spark plugs. I also replaced the fuel filter last week. The car is also backfiring every once in a while. I have a header, presilencer, and dual mufflers.......... no cats at all. What could be causing my car to buck like that? It runs fine while I am on the throttle, and idles fine. Only letting the car coast in gear will make it run like ***. Any input is appreciated.............

 

and btw, I have a Walboro fuel pump, brand new, at home, if that might be the problem. I was just hesitant to install it, because if my car is running rich I don't want to push even more fuel into the motor........... thanks....!

 

Could be a lot of things, I would do a compression check first, if compressions are good, then it might be the fuel system: sticky injectors most likely

 

Rich probably, just like mine. Some say its the TPS.

 

probly not but wouldnt hurt to check for warped rotors

 

When the car is coasting, not braking...