High Idle

[jackman]

I have a 1990 454ss truck that is idling high 1200 rpms. Ive replaced the intake and TBI gaskets it is still idling high. I applied vacuum to the EGR valve and the rpms drop to normal (700-750).
Does anyone know what else can cause this problem. All help is needed. Thanks!

[River Bum]

Mine did the same when I got it, it was the tbi plug (its called something) tbi sensor? When it was replaced it went back down to 840 if I remember correctly.

Good luck

Ron

[FieroSpeeder]

the egr valve is suppose to do that, so you know its working.


Does the idle drop after the truck is warmed up, if thats the case, it can be a coolant temp sensor. I would check it with a multimeter before replacing it to see if its good or not.

Your TPS can be off, and you can check that with a multimeter to see what the voltage is at closed throttle and WOT.


I changed a friends oxygen sensor, on his mustang, and it was causing it to be in a open loop, i guess the computer thought the car wasn't warmed up because the oxygen sensor wasn't giving off any readings.

[jackman]

Idle stays the same all the time. I have a scan tool it is saying myO2 sensor is working. I pulled the TPS off and checked it it is OK. Any more help is needed!

[River Bum]

Have you ran injection cleaner lately? Run (2) at the same time with a 1/2 tank of gas. Maybe the injectors are dirty?

Ron

[wileys_farm]

I've seen some trucks that around the intake the pcv valve hose(the one that goes from the throttle body to the pcv valve itself) get a pin hole in them and they will idle way up there. Pull the line off at the throttle body and check it for heat cracks and so on. It sounds like a vacuum leak to me somewhere. Listen closely around the intake, manifolds, the hot spots, this is where the lines will crack first.


hope i could help

wiley

[jackman]

I have replaced all the vacuum lines on it. Im checking the EGR valve solenoid now to see if it works other than that I dont know what to do. How would I check the IAC valve?

[wileys_farm]

still sounds like an intake leak somewhere. Start it first thing in the day before its drivin take ya some starting fluid and go around the intake and throttle body. If it idle'ls up you got a leak try this before you go out and spend money. Just dont spray starting fluid on the engine when its hot.

[jackman]

I have done that about 3 times now. When I apply vacuum to the EGR valve it self the idle goes down what controls the vacuum to the EGR valve is what I need know Im not real sure how all this vacuum stuff works. Thanks!

[wileys_farm]

Sorry I dont know anything about some of that vacuum stuff either. All of the aftermarket intakes I order are without the egr. In the manual that comes with the vehicle usually there are the vacuum routing guide(friend told me this). He said it could be under the hood also. Sorry I couldn't help.

[jackman]

Well back out to try something else Thanks for the help!

[gearhead748]

It might be a vacume leak. Easy way to find a vac. leak . this was tgg take a propaine thorch and take the pit off this will un screw and put a peace of vac. hose on it ( a foot or so will do) then turn the valve on just so you can hear the hiss then go all around the engine if there is a leak when you find it the rpm will drop right now then take it away and the rpm will go back up that a fool proof way to find a vac leak i do this all the time. let me know how this comes out