Major Dieseling/High Idle Problem

[dream on mcss]

Well it seems that since my friend dylan is never on here anymore, I have to post his problems with the car. Were having a major issue with high idling (2500rpm+) and dieseling after shutdown. The high idle started last thursday I think it was, when dylan had me go out to start the car to let it warm up after school while he was finishing up in auto. I let it warm up for atleast 5 mins, then I tapped the throttle to get it out of fast idle and it wouldn't go down, so I waited a few more minutes then did it again, still nothing. Well thats obviously a problem but nothing really major, but the NEXT day, when we got to school, parked, and he shut the car off it started dieseling BIG TIME. It lasted for about 10 seconds then it finally quit. It did it again today for about the same amount of time, so now we got a serious problem. I think the dieseling and high idle are the result of the engine running lean and developing hot spots which cause it to diesel. Its on the CCC system so I don't know how we can adjust the main jet, so any help would be appreciated guys. The high idle is so bad it causes the car to jump forward every time he puts it in gear. Anyway, I'm thinking its running lean, what do you guys think?

EDIT: Its a 305 4bbl on the CCC system.

 

[chevy2480]

Sounds to me like the distibuter moved and is now to far advanced or you have a vacumn leak causing a high idle.

 

[Bonnewagon]

I think your choke is not releasing.

 

[kyhunter89]

Lmk how this ends. I'm in the same situation with the same car. Only dieseled when someone else shut it off. But has been idling high at times. I assumed it was low octane gas seeing as its first time I put 87 in it and at a unfamilar station.

 

[ElCaminoGRAN/SPORT]

I think your choke is not releasing.

This answer sounds about right to me ,my olds 350 w/4b.carb does the same thing off and on and it happens when the choke gets stuck,fiddle with it and im usally good for a few weeks.

 

[megaladon6]

seconding the timing and check the carb for free range of motion on all parts. the one thing i don't like about Q-jets is all the linkage crap for the choke/idle speed stuff. a little bit of dirt or rust and one piece freezes, screwing something else up.

 

[megaladon6]

also, pull the plugs to check the color, this will give you a basic idea of the air/fuel mix.
if it's just carbon build up or anything like that, with it in high idle, spray water in the carb, as much as it will take with out stalling. this will steam clean everything.

 

[dream on mcss]

Well thanks for all your help guys, we just got out of school but when we started it up this time it didn't high idle at all and it's atleast 60 out so maybe the problem is the choke because apparently it only does it when it's cold. So what could the problem be? So I'm guessing it has something to do with the choke then, right?

 

[Bonnewagon]

If it's an electric choke the contact under the grey connector gets cruddy and the choke works intermittently, until it quits altogether. Sanding the contact works for a while, but the best fix is to solder a new wire to the connector then add a separate quick-connect. A hot air choke uses a tube that draws hot air from the manifold, and it gets clogged with crud and rust. It needs a hose to draw clean air from the air cleaner as it's source.

 

[othtim]

do you have a throttle return spring? are you sure the throttle is closing all the way when you release the pedal? for sure check all your linkages.
are you running really lean at idle?