1985 firebird, 350 with quadrajet, all factory except exhaust. Only shorty headers to a y pipe.

Seems to start and run great in the summer time. But when it gets cold out, it suddenly seems to idle high (around 1400 rpm) until I drive it for a bout a couple blocks.

Is there an adjustment for the choke that would correct this? It looks like the choke is riveted closed... the only adjustment screws I see are for the idle, and the other looks like it adjusts spring tension against a little green tab on the right hand side (passenger) of the carb.

I would love to be able to warm up my engine in the winter time at around 1000 rpm instead of 1400.

Any suggestions would be greatly appreciated!! Thanks!!!

 

1400 is normal for a cold start.

 

WHAT!?!?! You're kidding me!! it always used to run around 1100 at idle when it was cold outside. I would love to leave it sit and warm up for a few minutes in the morning, but I feel like it is just revving way too high for that much time.

 

Do you still have the underhood sticker that gives the various adjustment specs? It'll probably say high idle should be 2300, or something like that. That adjustment is done while the engine is warm, by manually engaging the high idle cam. When the engine is cold and the high idle cam is engaging on its own, it'll be much lower.

This is about how this all should operate:

Engine cold. Depress accelerator 1/4 to 1/2. Start engine.

At this point, the high idle cam is on the highest step. The choke butterfly will have closed completely before you started the engine. When the engine starts, vacuum is now applied to the "vacuum break", often called "choke pull-off". This should open the choke butterfly slightly (and there is a spec for that - see the q-jet sticky in the top section of this forum). It should also, after you tap the accelerator slightly, allow the high idle cam to drop down one step.

Now, the engine continues to run, either idling or you've pulled out and start driving (gently, because everybody knows an engine should be babied until it is up to full operating temperature). The choke heater relay has engaged, which is sending 12 volts to the choke thermostat, warming up the choke thermostat coil. As the choke thermostat coil warms up, it will start relaxing the force it has been applying to the choke butterfly mechanism. This will start opening up the choke butterfly gradually. It also allows the high idle cam to drop down a little more, but this won't happen unless the throttle is off-idle a little to release the force the high idle adjustment screw is putting on the high idle cam.

After 4 or 5 minutes of running and/or driving, the choke thermostat coil should have warmed up enough by now to completely open the choke butterfly, and let the weight end of the high idle cam to drop down completely (again, if the throttle has been off of idle to release the force on the high idle cam). This will also disengage the secondary lock-out lever from the secondary throttle shaft. At this point the high idle cam should be completely disengaged, and the curb idle screw controlling the amount the primary throttle blades are being held open.

Hopefully from this description, you can see the various things that could cause a cold idle to be too high, or stay high for too long.

First, perhaps the choke thermostat isn't closing the choke butterfly all the way (weak choke thermostat coil, improper adjustment, etc.). This could cause the high idle adjustment to have been improperly done when the weather is warm. Now that it is colder, the choke is closing farther, and hence now on a higher step on the high idle cam.

Or, perhaps the choke pull-off (vacuum break) isn't adjusted properly so that it doesn't open the choke doesn't open enough at first to drop it off the highest step on the high idle cam when the engine and weather are colder.

Or, perhaps the high idle speed is improperly adjusted.

Or, perhaps the high idle cam and/or choke mechanism is gummed up. Might be remedied by a can of carb cleaner spray.

In my experience, setting everything to the factory specs, with everything operating and adjusted properly (including the ignition timing) produced the best results. I did tweak the vacuum break and high idle adjustments when I put the 350 under the LG4 system to produce a little better cold start and early warm-up running characteristics. I made sure the vacuum break opened the choke butterfly enough to move the high idle cam below the first step for starters (after everything was initially set to factory specs, including ignition timing). It's been a little while, but I believe I also was able to settle for slightly less high idle warm RPMs than spec'd, but don't start there.

 

My high-idle is right about 2000rpm for my 84 TA with a 350 swap in it. It was 2400-ish before I turned it down. The "low idle" is around 1600 which I"ll normally kick down to right away if it's not freezing outside.

If it's really cold outside, like below 30*, I'm not sure 1000rpm would keep a carb running even with the choke set to that RPM.

 

I tweaked my 350 to run right at around zero degrees. It was fine under all other conditions.

The '82 LG4 that I ran from October to February was all set to factory specs, and ran fine when cold. The engine was pulled in February for an LS1 swap, or I could have told you how it ran in the summer...

I guess I should mention that both cars had a functioning thermovac air cleaner.