I have a 1993 GMC 3/4T Suburban 4x4. New engine/transmission w/20k miles. Runs

[Elocksa]

fine but check engine light on. The check engine light comes on when you start and stays on until the engine warms up. It does appear to be idling faster than you would expect when it is started. I have replaced the O2 sensor, temp sensor, done complete tune up (plugs, wires, rotor, distributor cap, air filter, fuel filter), and rebuilt the carburetor/injector (this engine has 2-port injection). My question is, why is the check engine light on and is this a problem?

 

[nyninchdick]

Get the OBD scanned for fault codes, or buy your own code reader with a manual of codes. It could be a simple fix, but don't spend a fortune until you find out exactly what it is.

http://www.autoshoppingcenter.com/techtools/EQUUS/code_reader/obd_3123.html

 

[mdcbert]

Before you start part swapping, go find out what the code means. Then come back and ask. Fast idle? it could be a vacuum leak, or a misadjusted Idle air control module. Too little information from you here to tell...