I have owned a 1986 300zx turbo for two yrs. and been having a terrible time getting it to run. I finally took to the dealer and had it check out. They said it was a TPS and harness that needed to be changed. I replaced the switch and the car ran like never before, with one exception. The day I had the switch replaced, when I got home and shut it off, it won't start again. It turned over like the timing belt had failed. the next day the darn thing started up and again ran like a champ, until I had to stop for gas. The next thing I now its on the back of a tow truck being taken home. You guessed it, once at home I tried to start it and it fired right off. So the question is, What would make the car operated in such a manor. I think it may be due the changing of the switch but others say it could be the coil or spark plug wiring.

Any and all advise will be welcomed.

pull one of the plugs out and place the wire back on i and ground it to the chassis and try to start it and see f you are getting good spark at the end of the plug..... also check your coolant temp sensor those will keep it from running also when its heated up..... u also said the dealer said u needed to replace the harness did you do that also u may have some wires breaking down when they get hot