High Idle "HELP"

[stytch64]

I have a 85 720 with the z24 and have a problem I can not figure out. I was hoping some one here might be able to lead me down the right path. My wife was driving the truck and said that stalled at a light, started right back up but she said the idle was higher than normal. She noticed that the Idle kept getting higher while she was at lights and the truck not in gear. She brought it home to me and the idle was way high, maybe over 2G. I have looked at everything I could think of and withe the idle screw all the way out I cant get it under 1300 rpm.I checked: Throttle cable, looked down bore for any blockage and did not see anything, tried looking at the linkage behind carb and didn't see anything evident. I then started with the vacuum lines and found that I might have a vacuum leak at the egr valve so I capped that off with no luck. My head hurts and I just don't know enough about this mixed up vac system that I am calling out for help. Has any one heard of anything like this. Thanks in advance.

[ben1]

Well nobody else is posting anything so here's a couple ideas. Have you tried unhooking the throttle cable from the carb altogether? Once had a similar high idle problem that turned out to be the pedal itself was binding up.

I'd track down and fix any vacuum leaks. Get a couple cans of carb cleaner and spray slowly over the whole vacuum line spaghetti mess. If the engine kicks down, you've just sprayed over the top of a vac leak and can fix it. Also spray between the carb and intake manifold to check for leak there.

If you don't have emissions tests where you are, you can take out most of the vacuum lines just leaving the one from the carb to the distributor and capping the rest.

Also, have you checked the operation of the choke and the cold start solenoid (or whatever that's called that puts it on high idle when cold), maybe it's binding up.

Hope this helps.

[lalsimmons]

I had a similar sounding problem, my mechanic said he "bypassed the EGR". I couldn't tell you how to do it, but it solved the problem.

[lalsimmons]

I have since removed all vac lines and I posted a lengthy set of pictures when I did it. My mechanic said to do it, along with a lot of people on the boards. I ended up having the timing done once the vac lines were all gone, but the truck is running well since.