what is this CEL

[TURB0]

I recently re-assembled my 91 gsx and went to fire it up. The car won't hold an idle unless I pump it and sounds as though it has some monstrous cams in it. I am pulling CEL 21 on my logger yet cannot find what this means. Any insight?

 

[Mr Peepers]

Diagnostic code 21 is the engine coolant temperature sensor, it is the lowest temperature sensor in the thermostat housing.

By the way it does not control the temperature gauge in the car, it tells the ECU when the engine has reached operating temperature.

 

[TURB0]

Would that greatly effect how my car runs?

 

[Old Mitsu Tech]

Back in days of old we had what was known as a choke. Flash forward to present day. No more choke. When your key is turned on, the first thing the pcm looks for is the coolant temp. If the engine is cold or perceived cold, the pcm tells the injectors to go rich as a cold engine needs a richer mixture than a hot engine. Here's the fun part. If the coolant temp shorts out and shows -40 degrees and the engine is warm, you are in for a very rich mixture. Go the opposite way on a cold engine and it won't start as the pcm thinks the engine is warm and reduces the fuel mix through the injectors accordingly. A very important sensor. Come to think of it, they are all important. It's just the coolant temp that the pcm looks at first.

Good Luck