:banghead: :banghead: :screwy: have a 96 grand am wih a quad 4. lately, if i use the cruise control on highway, engine will missfire/stumble, especially noticable when climbing hills. This problem will appear over 45 mph when cruise applied. if driving normal, car appears to missfire/stumble when traveling above 65mph and especially when traveling up hills. no codes present, and no lights on. changed all the normall stuff, coils, plugs, fuel filters, injectors, checked cat. still have problem. My thought is possably vacume leak that gets more pronounced once cruise is activated(cruise relys on vacume) car drives perfectly normal otherewise, starts, runs good, plenty of power-alwase,. the stumble will
ALWASE appear if i try to use cruise, will run fine for a sec, then start to stumble more and more....your thoughts please...thanks

Welcome to AF.

One thing you didnt list replacing is the boots for the plug if they have cracks it'll jump spark and misout.

Check you vacum lines to the Cruise box and all the others.
Could have a leak or something clogged up a little in those lines.

Also you said no codes, was it scanned with a cheap'o free scan or a GM Tech II scanner ?

thanks for gettin back to me. It was scanned with my snap-on brick. the boots were replaced. I'm thinkin vacume but i can't figure how low vacume would cause it to skip and buck. It will alwase do it if i use cruise. I have checked and rechecked the lines, everything appears normal. Anybody else in hear ever have this issue? thanks again, rich

....one more note, it only does this while at cruising speed once warmed up. above 60 while in 5th. drove it today without cruise and it will buck, just not as noticable. you really have to search to here/feel it. with cruise on, your riding a bull!!...thanks again

replace the spark plugs, and make sure they are gapped right, if that doesnt help check the wires.

xma1080, if you had read the earlier posts you would see that his car is a Quad 4 which has no "wires", they use boots.

Also his issues are only when the cruise is used, so I would say the problem is within the cruise system or its wiring.

Also thiers many things besides plugs and wires that can cause a car to misout at highway speeds.
Bad fuel, clogged injectors, clogged fuel filter, bad injectors or thier harness wires.

ok, my bad for not reading.