Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem

'81 Long/Random High Idle(s)

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MP81:
Hello there!

Ever since getting the car ('81 Z28, LG4 305) last year, the carb has always exhibited somewhat odd/random behavior.

When you start the vehicle up, it jumps to high idle (maybe a little higher than I'd expect) until the choke opens and the idle begins to come down. However, at some point, you'll hear it change, and it'll start increasing - all the way to about 2500 RPM, if you let it.

The only real way to get idle RPM to drop back down is the rev the hell out of the thing, and at some point, it'll drop down to 750 RPM, where it idles like a champ, though it likes to creep up to about 1k after that...

Sometimes, when you rev it when it's up high doing it's "thing", they're very slow to drop back down.

I remember earlier this year (prior to putting the car up on stands to install my headers - where it is currently still sitting awaiting my lazy ass to install the new exhaust) I was messing with it, because it had gotten really bad after the winter. I'm no carb expert, so bear with me on the terminology/descriptions, but the "rear linkage" (separate from the main throttle linkage) seemed to exhibit exactly the same behavior if I pushed on it while the car was idling - same sound of suddenly rising RPM, etc. I thought I had fixed it by playing with that a bit, but it seems to have returned.

I need to give the linkages all a good coat of lubricant (since I doubt that's been done in...well, maybe never), but I'm not sure if that'll be the entire solution.

Any idea what might be the culprit?

Thanks,

Kyle

Frank400:
Looks like and electric choke that is not working, or unplugged, or plugged but with no power (12v with ign on).

MP81:
The choke does seem to operate right after you start it, but checking for 12V with ignition on would be an easy test.

EDIT: Couldn't get a real good reading on the connection to the choke with the ignition on (but getting a good reading on the battery wasn't easy either, so I'll take another stab at it tomorrow) - regardless of that, I'm glad that I checked it, because it definitely was barely attached (terminal was too "open" and loose, so I closed it up a bit, and now it is tight on the spade).

Mudsport96:
I'm not as good as many of the guys on here, but there is a possibility that the choke coil is going bad. Just like anything else, it can wear out, so maybe its opening and then closing again instead of staying open. Something to look at.

Cliff Ruggles:
I see these problems frequently and exactly why we always replace the associated parts on those units.

I would replace the electric choke and the choke pull-off.  Adjust them per the factory service manual.  Also lubricate all parts involved with the choke and fast idle, and the problems will be corrected provided that you have a good voltage supply to the choke coil......Cliff

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