My 240sx has had numerous problems with acceleration and surging for quite some time and I have been unable to find the problem.

About a month or so ago, I replaced the 02 sensor, the pcv valve, cap, rotor, and coolant temp sensor. The car was fairly sluggish and was running extremely rich. I also advanced the timing a little.

It ran good for a few days and always runs better before the car warms up.

It is now VERY sluggish, with horrible acceleration and much more surging problems. Sometimes when backing off the throttle, it feels as if the brake is being tapped (best example I can come up with). It feels as if it wants to backfire occasionally, and still feels as if it is flooding from time to time.

My ecu reads codes 21 (ignition circuit) and 33 cts. I'm not sure if I haven't started the car enough to clear the readings, but I thought I had.

Someone PLEASE HELP!!!

Could a clogged cat cause my 02 to read incorrectly sending the wrong signal to the ecu? It always smells horrible after it is shut off and occassionally at idle (just not as bad).

Check your coolant temp sensor connection. The connector gets a green corrosion on it and causes high resistance. This causes a rich condition that shows up when hot.