No vacuum leaks found, flush and filled cooling system, No CEL codes, timing is properly set with new timing belt.. Car misfires occasionally for a period of time, the stalling seems to occur only when something with fuel isn't right or new (fuel filter, added a fuel injector cleaner, Etc.). Car has been runing good as of late but lacks power and going through fuel. 11.8 galllons only last around 150 miles (Mostly Highway). I have to shift down to all most 2nd to get it up large hills.

 

When you set the spark timing with a timing light, you must install the ECU test jumper like you would to read codes. If you do it with the jumper off, you will set it way retarded, causing bad performance and mileage like you describe.

 

My mileage dropped to 16 mpg, cat converter was plugged.