tmirish

'96 corsica, 105k, new plugs and wires, new cam position sensor because it broke when I replaced intake gasket set yesterday. No check engine light. When cold, starts fine, not much for fast idle, runs like the dickens to and beyond highway speed. When warm enough to move temp gage off cold, chugs and bucks under load as pedal is pushed until tranny downshifts to higher rpm and then runs fine again until upshift to start the process all over again. Tapped on the MAF sensor no go, no apparent vacuum leaks, no fuel in vacuum line to MAP sensor, PCV valve is clean and working. Beyond a slight hesitation at first punch, seems to rev up fine in park. I know this thing has about a dozen sensors and it can get spendy just replacing, just looking for a direction to start. Daughter's car trying to keep cost down.

Thanks.
Tim

heisabud

Sounds like a bad knock sensor.You do not say the make or type of vehicle?
Fuel quality verie's from brand to brand,a poor quality fuel will cuase pre detonation/a engine that "knocks". The quality of spark plug wires make a difference,the quality of the spark plug makes a difference,the quality of the ignition coils make a difference. The type of fuel additive you use makes a big difference also. I found that running a mild octane booster fuel additive increases the fuel mileage plus improves the engines performance. I installed Bosch irridium high performance plugs. Jegs high performance coil packs,morroso 8mm high performance spark plug wires. Why put all of this effort into a 91 2.2 liter Corsica,with 155000 miles on the engine? I run Pensoil high mileage engine oil, high viscosity rateing.No Sythetic oil.This only seem's get past my oil rings and smoke out the tailpipe. Why? Becuase I want my engine to last as long as possible,and to run the very best it canmto get the very best MPG possible.

tmirish

heisabud, you are exactly right about a bad knock sensor. Ended up paying a guy to use his high buck scanner and found the knock sensor was advancing timing too far when incorrectly sensing knock.

Thanks to all.