As a note. I disconnected the battery, reconnected, started the car. Ran for 15 minutes just fine. Once the car was fully warm (midway through heat - normal running temp) after about 3 minutes I revved the car to 1500 rpm. At this point, the car began to misfire, and the check engine light came on. Restarted the car, and it sits fine at idle. But when you rev the engine a few times, it will begin to misfire again. Just adding a note to the problem.

 

After doing the above, I then locked my keys in my car. Totally unrelated. Just a sign of my misfortune. LOL

 

Well, the shop diagnostic manual didn't offer much help. Although an interesting thing is fuel system re-calibratesjust beforewarm-up. The system runs open loop until then - ignoring the O2 sensors. When it re-calibrates, it uses the MAP sensor. I'd try to unplug the temp sensor and run until it's warm and see what it does. If it runs OK, i'd look at the O2 sensor (upstream), if it still misfires, look at the MAP. It almost sounds like it's starving for fuel (lean condition.)

 

OK. I will give this a shot in a bout 30-45 minutes and get back with the results. I really appreciate your help and if you can find time to check this thread later, that would be much appreciated. After calling 5 shops, one of the 5 said it could be a fuel problem. They would run a pressure test to make sure that it was getting enough fuel. I didn't think this would be related. But then again i'm not a mechanic.

 

More info. I don't know if i mentioned this before. But once it begins misfiring, it continues to misfire after i've released the gas. For instance, the car is warm, i start it, rev it, it begins misfiring. Then let it idle and it will continue to misfire until i restart the car. I've called a few auto placed. 2 out of the 3 that would speak with me said that it is most likely a fuel pump. But that doesn't make much sense to me. Based on all of this information. Would a fuel pump make sense to you?

 

Another question. You asked to remove the temp sensor. Where is this located on the 03' neon's?

 

Check the fuel pressure, that will tell you if it's the pump. I don't think it would be since it continues to misfire. It sounds like a control problem, but a fuel related control problem. The engine could be throwing the timing way off, which goes back to crank/cam sensors. You know how to check the fuel pressure?

 

I'm told the crank sensor wouldn't affect anything except the startup. No I am not aware of how to check the fuel pressure. Should I proceed with the removal of the temp sensor and let it warm up as a test. Or should I just take it in and get it looked at..

 

Check the fuel pressure with a tire pressure guage. There is a schrader valve at the end of the fuel rail by the injectors. The car should have the ignition on, but not running. I think around 50psi is where you should be, but I'd have to check for sure. Unplug the temp sensor and try it, it should only take a few minutes and might lead to a cheap resolution.

 

Can you describe to me the positioning of the temp sensor.. I'll try that before I take it in. Just not sure where the temp sensor is..