Hi, I just join this forum after acquiring a '90 firebird formula 5.0L. I dont have much (any) auto repair experience but trying to build my skills. So far the biggest repairs Ive done is replacing the heater core and thermostat in this vehicle.

The most prominent issue with this car is that it idles at about 2000rpm at startup. This is regardless of whether the engine is hot or cold. It will do this probably 7 out of 10 starts and continues to run this high (even when driving) for maybe 5-10 minutes until the engine finally slows down to a nice 650rpm. It does not run high again unless I turn off the engine and start it back up again... sometimes it will idle normally, other times its high.

The speedometer cuts on and off spontaneously while driving..I dont know it this can be related. When the speedo works, its accurate but when it doesnt, its completely dead. This seems to affect the engine speed slightly (I notice a small drop in rpm's when the speedo cuts off) but seems to have no direct correlation with the high idle condition.

What do you suppose the cause for this high idling is? Any suggestions?

Thanks!

 

I know on my firebird the car starts up and idles at around 1700 - 2100 rpms all year around. The reason for this is the choke mechanism is a carburetor and a similar mech in fuel injection vehicles. In the summer if you want the rpm's to go back down to around 700 just tap the gas after about 10 sec. In the winter you should just leave it as the engine warms up faster that way. The speedo problem is electrical. Maybe the computer in your car is going bad. That would explain everything. The computer went bad in mine with the guages failing and I replaced it noticing a boost in power.

 

try cleaning the throttle body to see if it makes any difference is the car sucking air anywhere cus a vaccuum leak will cause it too idle high

 

I will have to check for vacuum leaks but I figure it couldnt be a dirty throttle body since that would restrict airflow and have the opposite effect (stalling etc).
By computer, you mean ECM/ECU, right? ..the silver metal box underneath the passanger side dash?? ..is the a way to test is specifically aside from various symptoms?