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Hi,

My 69 Malibu, totally stock 350, has developed a problem with idle speed not returning to normal whem I let off the gas. It goes to a fast idle until I goose the petal slightly, then it drops down to normal. The choke works fine. I have used a lot of carb cleaner trying to make sure everything is very clean. Also, I replaced the throttle return spring. Neither helped. The car is a stick shift with no air...there is no "fast idle" solenoid. I guess something in the carb is sticking and the cleaner maybe isn't getting to it. Any suggestions other than rebuilding the carb?

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R.E. Stancliff
 

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check the high idle cam-when the car is cold the cam is placed into a higher idle mode. you have a black plastic choke housing that contains a coiled temperature spring. with the engine cold-unloosen the 3 screws on the side and open the throttle slightly-rotate the cover slowly until the choke butterfly moves backwards.you will have to make a few adjustment until its on the proper setting!!
 

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If it comes back to a fast idle when you back off slowly but returns to a slow idle when you whack the pedal, it is probably a worn throttle shaft. Grab the end of the shaft, rotate it a bit and try to wiggle it. If it wiggles noticeably, it is worn.
 

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On that model you probably have the choke coil mounted on the intake manifold with a tin shield over it. It should have a rod that goes from there to the carb. You need to bend the rod to adjust. The straighter you make the rod, the more your choke will open up faster. That in turn will kick you off of fast idle. What may be going on which is very common is the choke coil is not getting hot enough to open all the way. It uses the heat in the intake to warm up the coil. The crossover passage commonly becomes plugged with carbon and the only fix for that is to remove the intake to clean it out. Another possibility is that your heat riser is not working. That is the piece that goes between the right exhaust manifold and pipe. It has a flapper in it to close off the exhaust on the right and force it thru the intake passage to the left. That will heat the choke coil and also helps atomize the fuel for better drivability. Keeps it from stumbling like a lean condition. That flapper will become stuck open. It has a thermostatic coil to close and open it up.
 

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R.E.,
Check the simple(read that inexpensive) things first. There is a return spring that returns the arm to idle when you left off the gas. This can become "sprung" and worn out. Hit the "help" section at your local parts store and they should have a replacement spring. Careful when replacing this spring not to make it too tight, as it will feel like you are stepping on a truck gas pedal.

Let us know how this pans out for you.

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Better Late than Never Fred
Team Chevelle #400
ACES #4055
I'd rather have a bottle in front of me, than a frontal lobotomy.
1970 Chevelle Malibu
 

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All the advice above seems good...BUT FIRST:

Grab the steel fuel tube where it screws into the carb. Pull it from side to side, twisting the carb.

I got a dollar that says you can wiggle the top of the carb enough to change the idle speed. If it's loose enough, you'll do the same thing when you actuate the throttle. Slam the throttle shut, and the carb "wiggles" into it's low-idle position.

Correction of this REALLY COMMON (practically every Rochester 2G series carb is afflicted!)
problem is simplicity itself:

Pull the carb off, tighten the screws going UP from the cast iron base into the float bowl section. Put the carb back on, adjust idle speeds accordingly. You might not even need new gaskets, if you're really careful and somewhat lucky.

(Just did this on Dad-in-Law's '70 Skylurch!)

Of course, while you have the thing off the car and you're holding it in your hot li'l hands, you might wanna toss a carb kit and float into it...
 

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Keep in mind if you do have the black plastic choke on the side of the carb the car Must be OFF to make adjustment. Vacuum is applied to this housing which makes it hard to turn it the gasket is good, usually break the plastic housing if you try to adjust while car is running.
 
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