what is the purpose of the fast idle solenoid?my 1992 7.3 non turbo is running rough after i change the fast solenoid with one out of a turbo engine
The main propose is to help your engine warm up faster when it cold.
I am not sure right off the top of my head why the engine would be running ruff after you change the solenoid. The solenoid has nothing to do with fuel injection or air into the motor. Maybe the solenoid is out of adjustment.
Check the solenoid after the truck warms up to operating temp, if it still stuck out the solenoid is bad.
To do a quick test of the solenoid you can hook a jumper wire from the battery to the solenoid if it sticks out it good, if it does not it bad.
The solenoid is also adjustable, find a small wrench that fits the shaft head of the solenoid and turn it to where it is needed for your truck to idle at safe high idle RPM (1300 RPM is good).
Also you can splice a wire on to the feed wire to the solenoid, and hook it up to a switch in the cab powered by 12 volts. Flip the switch and BAM High Idle on a IDI.
Here's the most important part of installing the High idle switch!!
Get a diode from Radio Shack the .99 cents for a 2 pack, get 1n4004 diodes.
Install the diode with the stripe going towards the solenoid in the OEM feed wire. This keeps the 12 volts from your cab control switch running down the feed wire. Also keeps power from going to the sensor that controls the solenoid and damaging the sensor.