I have a 83 Cutlass Supreme with a 307,in the morning when I warm it up it will idle normal but after about 5 mins when it's warmed up it will idle high and I have to tap the gas and then it will idle normal, my question is why does it do that and how to I fix that?
High idle problem
- Thread starter Vega419
- Start date
- Status
That's how it's supposed to work. The question is what rpm is it fast idling at? I keep mine around 1500 to 2000 at start-up, and the adjustment for that is on the choke side of the carb down low. Only test at first start-up when the motor is cold, as even a minute of operation will heat the choke coil up. As it warms up, she drops down when you tap the pedal, but if you don't tap the gas at all, it will stay fast until it vibrates off the cam.
After a few minutes it idles really really fast I don't think it's sopose to be that fast, rpms are really going crazy and it only does it on a cold start up I don't know much about motors and I definitely don't know how to adjust it.... Could someone please explain
SmoknMali said:
No, it should be a 'hot air' choke.
Vega419, have you tried just turning down the fast idle? I'm sure you know where the normal idle screw is. Well it's NOT that screw. There's a different one on the passenger side of the carb under the choke housing. Turn that one to lower the fast idle. It won't effect your normal idle speed.
Read this first http://www.301garage.com/forum/index.php?topic=6098.0 and then look here for the adjuster screw.
I have an 83 Cutlass supreme that does the exact same thing.
On a completely cold start on the fast idle cam I set about 1750 rpm.
I let it warm a little on high idle/choke
if I dont bump the throttle to kick it down off the fast idle cams highest setting and follow the lower steps as the choke coil heats up, it will all of a sudden rev up to I would estimate 2000 or thereabouts. This occurs after a couple minutes of warmup time.
Then when I bump the throttle it will drop to normal hot idle, off of the choke cam.
I tend to think the wierd jump up in rpm is the computer adding timing or fuel or something, expecting the throttle to be off of the high step of the fast idle / choke cam?
wish I could see the programming of the ecm
On a completely cold start on the fast idle cam I set about 1750 rpm.
I let it warm a little on high idle/choke
if I dont bump the throttle to kick it down off the fast idle cams highest setting and follow the lower steps as the choke coil heats up, it will all of a sudden rev up to I would estimate 2000 or thereabouts. This occurs after a couple minutes of warmup time.
Then when I bump the throttle it will drop to normal hot idle, off of the choke cam.
I tend to think the wierd jump up in rpm is the computer adding timing or fuel or something, expecting the throttle to be off of the high step of the fast idle / choke cam?
wish I could see the programming of the ecm
I believe that the reason the idle goes up so high is very simple. When it's really cold, fuel atomization is poor, the air is dense, and all the metal surfaces are cold. Thus, a fast idle setting of 2000 rpm when ice cold, translates into 2500 or more rpm at operating temps. Because as the motor warms up, the EFE valve is directing hot exhaust gas under the carb, and the THERMAC air cleaner is directing exhaust manifold heated air to the carb. So as heat is added, fuel atomization improves, and the motor races. If you read the owner's manual, you are expected to kick down the fast idle as the car warms up, thus it shouldn't get to operating temp and the 2500 rpm while on the high step of the cam. You can't just start the car and go back inside for another cup of coffee like you can with a modern computerized car. These old choke cars are very hands-on, you gotta be there. An alternative is to set the choke rpm at the max you want it while unattended when at operating temp, say, 1500 rpm or so. The problem then becomes that when cold, the motor will chug and labor at around 800 to 1000 rpm or even stall until the heat comes up. This is because everything is cold and it is hard to set the vacuum break setting to work well at so low an rpm, it's much easier to set it for 2000 rpm. In summertime, you start the same car and it idles very fast, right? So you immediately kick it down. I try to set my fast idle as a compromise, fast enough to run well cold, but not too fast when hot. Ken's 1750 rpm is about perfect and rising to 2000 as it warms is to be expected. I would suggest adjusting the fast idle while the car is ice cold, with a tachometer, to run well at start-up. Then let it get hot and see just how high it races, and adjust it down to a comfortable rpm. By trial and error, you will eventually find the perfect setting for your car. The factory specs are a good place to start.
Bonnewagon said:
well put. that is exactly when I experience the scenario discussed.
the only other thing I would add to my previous post is that it is not a gradual rise to the higher idle speed. It is an immediate jump of at least 250rpm. Like flipping a switch.
It could be that the intake under the carb just reaches the temp needed to vaporize the fuel at that point.
The compromise setting may be the answer
- Status
Similar threads
