Fast idle problem

[ChevySepticGuy]

Hey guys,

Sorry for the amount of posts lately!  

I've noticed that when I'm driving the truck that she seems to run in fast idle all of the time. When I put her in Neautral and give her a shot of gas she will kick out of it, but as soon as i shift her into gear and touch the gas to accelerate she will go back into fast idle and stay there. (maybe this could be the reason for all the backfiring and stuff... mentioned in another recent post of mine).

P.S. It's the rochester 4 bbl.

Today I sprayed the carb and all related linkages with carb cleaner but haven't noticed much difference...there was a lot of gum on those butterflys though.  

I hope i don't have to mess around with my idle screws. I'm scared of screwing her up! the whole 1 and 1/2 turns and all that stuff always freaks me out because i tend to "over-do" things sometimes!...lol

"Chevy Septic Guy"
1985 Chevrolet Custom Deluxe C30 (1 ton) 350.

Edited by: ChevySepticGuy at: 7/5/06 3:29 pm

[gpday06]

does it do it when its hot outside? because my '79 C10 350 does the same thing, except when its really hot outside, so ive been thinking its the choke, but dont know for sure

[thirstycanadian]

I was having the same problem recently.  It would stay in fast idle unless you bring it down with the brakes.  Really annoying that you can't bring your speed down on the gears.  Plus when I had to shut it off in fast idle it dieselled like crazy.

On mine I found a little vacuum motor attached to the front drivers side of the carb which was holding the throttle open.  I forget what my mechanic called it over the phone (dash-something? help me out, cause I know you guys know more than me).  Apparently its purpose is to slowly close the throttle when you suddenly let up off the gas.  I guess this is to keep it from snapping shut and potentially causing a backfire.  I think it is an emissions add-on as well.  

I pulled and plugged the vacuum line going to it to see if that was causing the idle to stick high and it was indeed the culprit.  With this vacuum motor disabled I am not noticing any difference in how it drives.  Nothing more than the normal (normal for my truck at least) little lick or snap from the tailpipe when I get off the gas for shifting.  I haven't tried it at highway speed yet, but it seems normal so far.

Good luck