I have a 1988, 351W, 4X4, pickup that I recently rebuilt the engine in. It runs fine at times and at other times, it idles very fast (approx 1800 rpm). I can hear like a solenoid clicks and then it runs fast. Sometimes the idle will fluctuate, and sometimes it idles fine. I have changed the computer, the temp sensor, air temp sensor, and the idle bypass valve. Still I have the same problems. Acts like a vacuum leak, but can't find it if it is there. Any help would be appreciated.

Thanks
Jim

 

When it is doing the radical idle, push the egr valve in if you can and see if it changes the idle. If it won't move or changes nothing, bad egr valve. How are you checking for vacuum leaks?

Toby

 

Hello- Welcome to FTE! I have moved your post to the specialized forum we have here for your question. Check out the list of tech forums we have here. There is a wealth of information and expertise here to help you. There are a number of links in my sig below to help you also. Have fun!

 

I had the same idea, so I blocked the EGR valve off in an effort to rule it out. There was no change in the way it ran. I have sprayed WD40 and also tried water along the areas where I might have a leak. You should also know that I have removed the smog pump and all plumbing for it. Also plugged the holes in the back of the heads. The only vacuum I am running is for the power brakes, MAP sensor, heater, cruise, and the modulator valve on the transmission. All the vacuum solenoids are unplugged and have no vacuum going to them. I appreciate your help.

Thanks
Jim

 

Try using brake clean or if you have a propane torch, put a hose on it and run it along all the intake area( not lit of coarse) it will change the rpm's if there is a leak.

Toby