Friend rebuilt, rough idle when cold, better warmed up. Do not know proper setting for rich/lean adjusting screw. Or if out makes it leaner or richer.

Hi Alan:
A bit more info would help, like what kind of vehicle, and any symptoms.
Check the inside of the exhaust pipe. sooty is rich, dry is leaner.
Check the spark plugs. sooty is rich, dry is leaner.
Check the mixture. screw in for leaner. If RPM increases, it was rich. If RPM decreases, it is already lean.

Believe it or not you just said the solution to your own problem manufacturers specs requires for any adjustments to engine idle or other carburator adjustments to be preformed while the engine is idling and at normal operating temp in plain english let the car warm up then make your idle and mixture adjustments if this doesnt solve it i would check the auto choke and make sure it is opening at normal operating temp hope this helps good luck

no-- plugs will not be the problem. More likely a vacuum leak from a hose left off somewhere. If a carby engine it will be the idle mixture screw out of adjustment check ignition timing is set at the correct advance point

It could be that you have to adjust the idle mixture screw a little . It may be set too lean or too rich which gives what you describe When the engine is at operating temperature turn the screw in or out a bit until the motor runs better. Adjust then until it starts to run rough then screw it the other way until it starts to run rough again. Correct mixture will be in the middle of those points.

Is it hard to start? The choke has some notches on the side by the electric choke plug...rich to lean...If hard to start cold, loosen choke screws on side and turn the dial toward close (rich) retighten adjustment screws and recheck performance...If choke stays on to long after warm up (idles fast) adjust the choke toward open or lean position. Try no more than 2 notches either way between tests...Hope this helps.

Cheap air/fuel gauges simply tap off the stock oxygen sensor. That sensor can only tell you lean or rich and the car should idle roughly at 14.7:1 and go rich under acceleration. Cruise down the highway at steady 50 mph and see what the gauge does. Should be calmer.
At idle the needle can bounce around quite a bit. Means nothing. It should however go sometimes rich and sometimes lean. That's how the computer adjusts, if it stays lean too long, the computer tweaks the injectors richer. If it stays rich too long, the computer tweaks it leaner. If the computer cannot adjust the ratio, it will set the check engine light and in that case it should be a flashing check engine (meaning stop the car and tow it to a shop - flash means the catalytic converter can burn out).
If you want to know the actual air-fuel ration you need to buy a wide/band oxygen sensor and related gauge. They are much more expensive and will typically run a few hundred dollars. If the car is stock except for K&N, don't bother with the air/fuel gauge.
As for computer hookup. Go read up about "LT1Edit". Don't buy the software (too expensive for a stock car) but you'll understand what software is out there to monitor your engine (and what hardware you need to buy in order for your laptop to talk to your car).

should adjust the butterfly to about 3/8" opening at 50 degrees farenheit when engine is cold. Usually about 1 mark to the lean side on the choke spring housing. If unsure set the choke to the center mark than richen up one mark at a time until the engine starts and idles up when cold after properly setting choke by fully depressing and releasing the accelerator before cranking. If it doesn't idle up enough turn up the fast idle screw 1/2 turn at a time. Another common problem with the YFA is the choke heat riser tube rusting off at the manifold and the choke not unloading when the engine warms. Install a new riser tube after using a drill bit the same diameter as the tube to drill out the remainder of the old tube in manifold before inserting the new tube and attaching to choke housing.

mcdevito75 here, The fast idle is needed when the engine is cold to make the air and fuel mixture rich to keep the engine running while cold, the carb. choke doew this with a bi-metalic spring in that balck round box on the side of the carb, a screw also hepls keep the choke closed until warm up, this screw can be adjusted tpo control how tight it holds the choke cloesed, here"s how to adjust this screw to slow fast idle speed, Locate on the carb, where the gas pedal connects, have a friend operate the gas pedal with the engine off, once you locate the linkage, you"ll also see 2 screws with springs around them, 1 is for fast idle the other for regular idle, you want the fast idle screw, notice this screw will lay against and Half moon shaped tab, while the other screw lays against a shaft, you need the screw that lays against the half moon shaped tab. Start the engine and step on the gas pedal slightly and relaease, at the screw that lays against this half moon, simply turn it counter clockwise or toward you just 1 2 or 3 turns very slowly, you'll hear the fast idle come down but you don"t want the fast idle to low, listen to the engine very carefully, slow it down just a bit, it should still race though but not out of control. Of course for a full carb, adjustment the shop should handle that., but this info will help.

If it only has 500 miles on it I would drive it awhile before doing anything. It could be the rings just haven't seated in yet.

Although this isn"t a proper fix, and may affect emissions, I ran accross this problem on a friend's 87 2wd wagon.

There is a dashpot that controls a lever the Idle set screw is on, I am guessing it is a decel valve that closes butterfly when coasting in gear. I never looked at a manual to figure out what controls the vacuum valve that is on the passenger side of the engine compartment, but if you disconect the vacuum line and plug it that lever will not back off and idle will remain where you set it with the adjustment screw.

Make sure the engine is warmed up and not on a fast idle cam before adjusting idle.

The car is a 5 speed, I not sure if automatic cars are the same.

The car idles fine now and still run's great and gets 37+ MPG with 240000 miles!

If you want to fix it properly you would have to diagnose why that dashpot is being actuated at idle