1992 tbi 350 won't idle

My truck has been cutting up lately. It idles too low hot and cold, it runs well otherwise. I've change the temp sending unit in the intake, its got a new Accell distributor cap and rotor, a new MSD coil, and AC Delco wires and plugs. I replace the tps with a spare I had and that made no differance. I also used a spare AIC motor, that help for a while but its right back where it started. No check engine light present. Any ideas? Thanks

A couple more possibilities.

EGR & PCV.

you can also check vac lines for cracks. the TB has a gasket kit avail because they dry and leak.

The egr is working, and there is a good pvc with a new line on the truck. wouldn't a vac. leak cause the truck to idle high? mine runs at around 400 rpm, it cuts off sometimes when at a light or I lift the throttle suddenly.

The egr is working, and there is a good pvc with a new line on the truck. wouldn't a vac. leak cause the truck to idle high? mine runs at around 400 rpm, it cuts off sometimes when at a light or I lift the throttle suddenly.

A small vacuum leak would cause an idle increase. However a large vacuum leak, such as an EGR vlv not closing all the way due to carbon build up, will cause an engine to idle down and/or die.

Also the injectors could be clogged or the fuel pressure is too low. Or maybe they are running too rich.

Pull the spark plugs and have a look at them to determine a too rich or too lean condition.

Also if a different IAC worked for a while and then went bad again you need to look at the wiring.

I decided to replace the IAC motor again with a new one, I didn't realize they were that cheap, $22.95 @ autozone. The truck now idles like it is supposed to. When I removed the old IAC motor the plunger was fully extended and I couldn't make it retract, its now in the bottom of my waste can. Thanks for the replies. :biggrin:

I decided to replace the IAC motor again with a new one, I didn't realize they were that cheap, $22.95 @ autozone. The truck now idles like it is supposed to. When I removed the old IAC motor the plunger was fully extended and I couldn't make it retract, its now in the bottom of my waste can. Thanks for the replies. :biggrin:

just for future info do not try to move the IAC valve. also do not use carb cleaner on it.

throttle body cleaner is used with a soft brush [like tooth brush] to loosen the carbon deposits.

just for future info do not try to move the IAC valve. also do not use carb cleaner on it.

throttle body cleaner is used with a soft brush [like tooth brush] to loosen the carbon deposits.

Why not try to move the plunger? In the repair manual for the truck it says to toggle the plunger back and forth while keeping light pressure on it, to retract the plunger before installing.
I probably shouldn't have but I washed the whole throttle body, inside and out, down with carb. cleaner. I can't tell it runs any better but it looks better. What will carb cleaner hurt that throttle body cleaner won't, just for future info. Thanks J cat

Bear in mind that most carbs have no electrical components (except electric chokes), whereas TBs have a myriad of emissions control devices that are electric or electronic, composed of circuits, wires, servo motors, and electromagnets. Carb cleaner's solvent makeup is formulated to cut through carbon and varnish buildup without regard to anything electrical in nature.

The IAC valve is an electrically controlled plunger. If the carb cleaner gets inside the valve body it can soften the insulating glue or wire insulation, gumming up the mechanism, rendering it useless. If at all, it should only be used on the plunger portion to remove carbon deposits...do not immerse it. TB cleaners use solvents that are more friendly to the electrical components.

Only new IAC valve pintles can be adjusted using the wiggle method.

Hope this helps!

the carb clean destroys electrical componets...sure looks good nice and clean but the electrical is destroyed...the IAC is a motor and the gears may be damaged with any attempt to rotate..if you do get this to move now when re-starting it will have to readjust to the proper position..

you also have rubber gaskets/seals these also get destroyed by carb cleaner...

carb cleaner is only for metal...............