2002 ENVOY. THE TEMP DROPS AND THE ENGINE WILL RACE. THIS HAPPENS WHILE DRIVING AND SOMETIMES WHEN STARTING, EVEN IF ENGINE IS WARM, THEN IT WILL GO BACK TO NORMAL. WHAT IS CAUSING THIS? SOMEONE GAVE ME AN ANSWER OF A19.....NO HELP.

Are your fans working

Sounds like the thermostat is sticking, on warm up on lot of vehicle the gauge goes past normal and when the thermostat opens drops back. If it is going higher than normal, the thermostat is opening late. Needs changing before it stops opening altogether.

Try putting a fuel pressure gauge on the injector fuel rail. Start the engine then turn it off, the pressure should hold steady not drop to zero. If it drops you have a bad injector leaking fuel into the engine. Also smell the oil to see if it smells like gas.

see if the radiator fan is it running even when the engine is at C or at heat
if its running when its at C the thermostat is not working properly
do you keep the windows open when you are driving can be a reason
as the car has a radiator in side also which gives you the heat

Sounds like throttle position sensor is not working properly.



Good luck

mai

Sounds like a faulty sensor, if the actual temp is 195/215. The ICM is processing the information it receives from the sensor and performs accordingly. A complete diagnostic scan would be helpful in determining the proper repairs needed to correct the problem.
Good luck...i hope this helps, please rate me a fixya.

replace your ignition module this vehicle had a overheated module problem

check coolant level ,must be low ,chck for coolant loss

you have a side post battery that sometimes appear to be tight but may not be check for corrosion and tightness

ck fuel pressure