What is causing this high idle?
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Car: '88 Trans Am GTA; '84 Trans Am
Engine: L98 350TPI; 5.3 LSx built
Transmission: N/A; T56
Axle/Gears: 3.70 9 bolt; 3.73 10 bolt
What is causing this high idle?
I am trying to figure out why my car is idling at 1900-2100 rpms. Its a steady idle but it is obviously way too high. I have an L69 carb on an 87 LG4, since the car is an original L69 and I swapped a whole host of L69 parts from the original motor to this one its sort of a hybrid of the two motors. I didn't touch the wiring harness though.
So far I've replaced a bunch of the valves, (were stuck or old), ditched my smog pump as that siezed up, plugged my AIR tubing, plugged a couple other openings, no Cat converter, and the timing is good, idles smooth, has power, etc etc etc. So where the hell is the high idle coming from? I can't figure this out. I don't want to drive the car the way it is now. Previously it would die as I come to a stop. But it drives great. What am I missing here? I also have a new choke on the carb as well. Carb might be all original from the factory.
So far I've replaced a bunch of the valves, (were stuck or old), ditched my smog pump as that siezed up, plugged my AIR tubing, plugged a couple other openings, no Cat converter, and the timing is good, idles smooth, has power, etc etc etc. So where the hell is the high idle coming from? I can't figure this out. I don't want to drive the car the way it is now. Previously it would die as I come to a stop. But it drives great. What am I missing here? I also have a new choke on the carb as well. Carb might be all original from the factory.
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Car: 82 Berlinetta/57 Bel Air
Engine: LS1/LQ4
Transmission: 4L60E/4L80E
Axle/Gears: 12B-3.73/9"-3.89
Is the choke opening?
You didn't mention any attempt at adjusting the idle speed. Most likely the fast idle cam isn't dropping down (see "Is the choke opening?" above). It could be help up by the choke not opening, or not dropping down when the choke opens due to stickiness (gummed up, dirty, jammed, damaged, etc.).
You didn't mention any attempt at adjusting the idle speed. Most likely the fast idle cam isn't dropping down (see "Is the choke opening?" above). It could be help up by the choke not opening, or not dropping down when the choke opens due to stickiness (gummed up, dirty, jammed, damaged, etc.).
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Car: '88 Trans Am GTA; '84 Trans Am
Engine: L98 350TPI; 5.3 LSx built
Transmission: N/A; T56
Axle/Gears: 3.70 9 bolt; 3.73 10 bolt
Re: What is causing this high idle?
Is the choke opening?
You didn't mention any attempt at adjusting the idle speed. Most likely the fast idle cam isn't dropping down (see "Is the choke opening?" above). It could be help up by the choke not opening, or not dropping down when the choke opens due to stickiness (gummed up, dirty, jammed, damaged, etc.).
You didn't mention any attempt at adjusting the idle speed. Most likely the fast idle cam isn't dropping down (see "Is the choke opening?" above). It could be help up by the choke not opening, or not dropping down when the choke opens due to stickiness (gummed up, dirty, jammed, damaged, etc.).
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Car: 82 Berlinetta/57 Bel Air
Engine: LS1/LQ4
Transmission: 4L60E/4L80E
Axle/Gears: 12B-3.73/9"-3.89
How to verify choke operation:
With the engine cold, remove the air cleaner. Plug the port for the vacuum line that goes to the air cleaner. Open the throttle a little, the choke butterfly should snap shut. This should cause the green weight on the passenger side of the carb to move up (that is the fast idle cam). Start the engine, the choke butterfly should open slightly (pulled open by the vacuum break, aka "choke pull-off"). As the engine warms, the choke butterfly should continue to slowly open until it is vertical after 3-5 minutes. After the choke is fully open, blipping the throttle should cause the green weight to drop back down.
If any of these things does not happen, you've got some sort of choke problem (even if it has a new choke thermostat). The one most closely related to your described problems is the green weight dropping down after the choke is open and the throttle is blipped.
With the engine cold, remove the air cleaner. Plug the port for the vacuum line that goes to the air cleaner. Open the throttle a little, the choke butterfly should snap shut. This should cause the green weight on the passenger side of the carb to move up (that is the fast idle cam). Start the engine, the choke butterfly should open slightly (pulled open by the vacuum break, aka "choke pull-off"). As the engine warms, the choke butterfly should continue to slowly open until it is vertical after 3-5 minutes. After the choke is fully open, blipping the throttle should cause the green weight to drop back down.
If any of these things does not happen, you've got some sort of choke problem (even if it has a new choke thermostat). The one most closely related to your described problems is the green weight dropping down after the choke is open and the throttle is blipped.
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Engine: L98 350TPI; 5.3 LSx built
Transmission: N/A; T56
Axle/Gears: 3.70 9 bolt; 3.73 10 bolt
Re: What is causing this high idle?
In case the weight is not green as you describe, do you have a picture of it somewhere so I will know what I am looking for.
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Car: 82 Berlinetta/57 Bel Air
Engine: LS1/LQ4
Transmission: 4L60E/4L80E
Axle/Gears: 12B-3.73/9"-3.89
The handy-dandy E4ME service information sticky, https://www.thirdgen.org/forums/carb...e-rebuild.html . Scroll down to Figure 6C1-21. Item #37, "Cam-fast idle".
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Car: '88 Trans Am GTA; '84 Trans Am
Engine: L98 350TPI; 5.3 LSx built
Transmission: N/A; T56
Axle/Gears: 3.70 9 bolt; 3.73 10 bolt
Re: What is causing this high idle?
Ok, I found the green parts you were talking about on an LG4 carb I had laying around, then compared it to the L69 carb to find the weight. I didn't follow exactly what you told me but what I did (air cleaner and etc were already removed) was hold a finger over the vac port, then threw the choke all the way open. The choke butterflies went vertical when I did this. Moving my free hand over to the other side I pulled the throttle. When I did that the choke snapped shut. (I'm trying to avoid running the motor unless I really have to because I'm not sure if my car is charging either, but that is a problem for another day I want to get it idling lower so I'm not working on a motor that is idling like its doing 80 on the interstate).
Because of the snapping shut I'm assuming (if I understand it correctly) that the choke is working right. Naturally I should probably fire up the car to be 100% sure.
Because of the snapping shut I'm assuming (if I understand it correctly) that the choke is working right. Naturally I should probably fire up the car to be 100% sure.
Last edited by L695speed; 09-23-2009 at 12:24 PM.
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