1990 Corvette TPI, overheating and high idle.

I am baffled at the moment. I Just picked up this 1990 Corvette with the L98 TPI. The motor was replaced with a Jasper Class 1 performance engine 7,000 miles ago. Now, I had some problems with the cars idle. I was told it may have been the IAC valve so I replaced that. Only for it to know make a horrible hissing noise which means a vacuum leak, I never reset the valve properly since I do not know how!

But the worse of problems is the overheating. Starting 2 weeks ago, whenever I am driving the car for a at least 30 minutes, the car will start to heat up while sitting at idle. If I have the AC on, the car will not heat up as bad. I have noticed the car is able to heat up to almost 260*F whereas normal temp is 190*F- 210*F. Oil Temp will get to almost 210*F at most. I just changed the Thermostat to a 160* stat, also refilled the system with 50/50 green antifreeze. I bleed the enitre system out, and noticed water flow. However, at times I do hear the fan will not kick in, then sometimes it will at the proper time. I am not leaking any fluids, and the previous owner allowed the car to sit a majority of the time. I just changed the oil, 10w-30. It is still a factory car outside of the motor and the T-stat.

to add: If I have the AC on from start-up to shut down, the car will stay at the 160* stat's operating temp. If I have it off, the car will be ok as long as I am consistantly moving. But if I am idleing or slowly moving in traffic, it will heat up and heat up quick!

Please help! I traded a perfect trans am for this piece! I am hoping its just a relay problem!

thanks Ryan
Do you
have the same problem?
Tuesday, August 21st, 2007 AT 11:55 PM

1 Reply

With the A/C off at idle check to see if your cooling fan comes on. There are usually 2 fans 1 for normal operation, and 1 dedicated to the a/c.
If the temp sensor is NG, on your car the ecm is supposed to keep the fan on full speed. Check the fan relay! If it's NG the ecm can't run the fan!
If it overheats and the gauges show hot test the coolant temp sensor with a scantool.
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Sunday, August 26th, 2007 AT 7:55 AM

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