I have a '90 240sx and it bucks occasionally. It is completely stock and has a manual transmission. The clutch was replaced by a mechanic 10,000 miles ago. The whole car has 90,000 miles on it. In the lower gears (1st and 2nd) it likes to buck very badly if I shake my gas pedal foot in the least bit. It like it is hypersensitive to gas pedal input. Say I go over a speed bump in a parking lot: my foot shakes a little bit as I go over the bump, that makes the car jerk a little bit, that little bit of jerking makes my foot shake more, and soon enough the car is bucking away like a BRONCO!!!!! The only way I can stop it is to try my damnedest to kep my foot perfectly still or to let off the gas completely or to push the gas hard. There are other situations where this problem occurs, it even occurs sometimes in stop and go traffic unless I concentrate very hard on keeping my foot perfectly still. I have driven my friend's 240sx and his does not have this problem. I have replaced the motor mounts and the transmission mount with the hope of curing this problem but it did not help. The rear suspension seems to be solidly mounted with no bad bushings or components. The rear shocks are original, so they arent dampening as well as new, but I wouldn't say that they absolutely NEED to be replaced yet. Everything on the car works flawless except this, please help me

Check and make sure the throttle cable is not adjusted to tight. Also this could be a sign that the throttle position sensor maybe bad at the lower throttle opening.

Thank you for your response. When you say "Check and make sure the throttle cable is not adjusted to tight" are you suggesting that perhaps tightness in my throttle cable is leaving the butterfly too far open, and the computer is compensating by shutting the idle air control port in the throttle body in order to maintain an idle speed that is not too high? How do I know what is the right adjustment for the throttle cable to be in? How is it adjusted properly?With regards to the TPS sensor, wouldn't my check engine light be on all the time and wouldn't the car run terribly if the TPS was broken? Can the TPS sensor be out of adjustment? If so, can it be adjusted easily?I have noticed that every once in a while my check engine light will come on for maybe 10 or 15 minutes while I am driving, but then it will go out by itself. The car still drives the same even when the check engine light is on. This used to happen maybe once every couple of weeks, but lately it's been occurring several times a week. I haven't noticed any big change in the way the car drives in the past couple weeks though. Does my computer store any trouble codes even after the light has gone out? How can I access the codes? Is the code reader inexpensive? Thanks again, -Quin P.S. If it's of any help: I have had the car for 5 months now and it has always done that bucking that I spoke of, it has neither gotten better or worse during this time. I also have noticed that I sometimes get what feels like clutch chatter when I am starting from a stop

Maybe a dumb answer but just trying to help, could it be O2 sensor? i know with my monte carlo ss , same symptons and that was the problem. ..............

By "same symptoms" do you mean the bucking in the lower gears or do you mean the check engine light coming on and off occassionally. I have fixed the check engine problem by reading the codes off the computer. Computer said I had an egr problem so I looked under the hood, while I was under there I noticed one of my injectors was leaking fuel. As I was fixing the injector leak I noticed that a vacuum line leading towards diaphragm of the BPT valve was ruptured, along with another random vacuum line near the back of the cam cover. I fixed the injector leak and vacuum lines, but still have the goddam bucking. Perhaps the bucking has gone down a teeny bit, but that could just be the placebo effect, because it is still definitely there.