i need some input. History: Bought car 8 mo ago not running. replaced opti, mas air, tps and plugs. Finally ran good for about a week. Devoloped a miss under load(not noticable at idle or reving motor). thought it was fuel related. machanic says fuel press is good and no vacum leaks that he can find. it has no codes. opti was an ac delco. miss is not bad when motor is cold, gets worse as it warms up. any suggestions? 95 formula, t56, no mods. thanks for all the help.

 

O2's

 

Did you put new plug wires on it too? If not, I would try a new set.

 

How many miles? Like someone said the 02's are a likely culprit. If you have access to a scanner you can verify them to be bad or good. Check the plug wires since you replaced the plugs one might have gotten to close to the manifolds and got damaged.

 

If you don't have a scanner, you can check the O2 with a multimeter. There are 4 wires that go to the O2. Two are the same color (brown on my 96) and go to the heating element in the O2. The other 2 send a signal to the PCM, these are the wires you want test the O2 from. Get a couple sewing needles and push them up into the back of the connector far enough to make contact with the pins inside. Start the car and let the O2 come to temp. Set the multimeter to DC volts and measure the voltage at the two needles. The voltage should jump between 100mv and 900mv if the O2 is good.