Mitsubishi Repair: my mitsubishi colt engine problem, mitsubishi colt, radiator fan

Question
i have a 1992 mitsubishi colt 1.3 gli and the problem is i started
today in the morning and everything was ok until in the
afternoon i was driving normally and the ''check engine'' warning
lamp came on everytime i engage into 3rd gear and get to
40mph but it does not do that 0n 1st,2,4,5th gear,i have
checked the engine oil and the water everything seems to be
ok.but i was wondering could it be the radiator fan not working
because the temp gauge is on half not cold nor too hot,could
you please help me with the situation.

thanks,,  

Answer
Jeremiah,
That's an interesting problem. Does the CEL (check engine light) turn off if you go from 3rd to 2nd?  It's possible your engine temp. sensor is malfunctioning, but you'd most likely have  performance problems.  If your car is running fine with that CEL on, you may have an emissions problem.  There's little difference between 3rd gear and 4th gear, so it's strange this only happens in one gear.  I'd also recommend you check yoru car's computer.  You can read this article for more information:
http://www.90gsx.com/eclipse/cap/caps.htm

If your ECU is malfunctioning, all sorts of weird problems can happen.  Remove the ECU and visually inspect it.
Good luck!