LG4 High Idle - Team Camaro Tech
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post #1 of 12 (permalink) Old May 1st, 99, 11:09 AM Thread Starter
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I have an 86 IROC with an LG4 and a Q-Jet. Lately, I've been having problems with high idling. I have had problems before, and at first I thought it might be the choke sticking, but I'm not so sure anymore...

Here's the problem. When I first start the car, It'll idle around 2000-2500 RPM. Usually after a few minutes the engine will rev a little higher, at which point I can kick it down to a normal idle. Now, however, if I attempt to kick the engine down, it will just hover around 2000-3000 RPM.

If I let it warm up for an exorbitantly long time, or if I shut it off and re-start it, I can get the engine to kick down to a normal idle, but when I rev the engine up to about 2000 rpm, it will "stick," that is, it will start idling high again until I kick it down.

Usually I can let it warm up after I kick it down and it will operate normally, and I have tried spraying both the throttle linkage and choke with Gum-Out. It appears to help at times, however whenever I start the car I have the same problem. It may be a vacuum leak, but if that were the case, it would idle high ALL the time, wouldn't it?

Sorry for being over-detailed, but I think the more I say, the easier it'll be to understand the problem. Any ideas would be appreciated.

Mark
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post #2 of 12 (permalink) Old May 2nd, 99, 07:45 AM
 
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THE THROTTLE RETURN SPRING COULD BE A PROBABLE CAUSE IF NOT ITS MOST LIKELY THE CHOKE
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post #3 of 12 (permalink) Old May 2nd, 99, 07:46 AM
 
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THE THROTTLE RETURN SPRING COULD BE A PROBABLE CAUSE IF NOT ITS MOST LIKELY THE CHOKE
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post #4 of 12 (permalink) Old May 2nd, 99, 07:46 AM
 
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THE THROTTLE RETURN SPRING COULD BE A PROBABLE CAUSE IF NOT ITS MOST LIKELY THE CHOKE
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post #5 of 12 (permalink) Old May 2nd, 99, 09:44 AM Thread Starter
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Thanks for the info.

I thought about that...I sprayed the throttle linkage on the side with Gum-Out last time...it feels more like the throttle's sticking but the actual lever where the cable connects seems to be moving back normally.

The weird thing about it is that when I'm having the idle problems, the choke is actually further open than when it's idling normally. I thought it idled higher when the choke was shut. Would the choke being too far open at idle cause the same problem?

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post #6 of 12 (permalink) Old May 2nd, 99, 01:48 PM
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sq,
How many miles does the carb have on it ? Q-jets are sort of known for the throttle shafts getting worn out after a while, and they will cause this type of problem. Also, make sure you do not have a vacuum leak somewhere, that will also cause a fast idle.
You mentioned cleaning the throttle arm side of the carb with "gumout". How about the choke side ? There is a fast idle cam that moves with the choke and if it is sticking it will keep you on fast idle. It only moves by gravity so if it gets gummed up it will cause the problem. You might want to take the "gumout" can to the choke side of the carb also.
The newer cars generally have a very short choke opening time because of emmisions standards. There is a vacuum can called a "choke pull off" that should pull the choke open some as soon as the car starts. If this "pull off" gets a leak in its diaphram, it will not open the choke, and will also cause a vacuum leak. Last but not least, make sure the electric choke heater has not burned out and is not opening the choke completely. I know you said it was open but make sure that airflow was not doing it. If you shut the car off hot, the choke should be pushed open pretty good. Hope this helps, let us know what else you find.

------------------
Bill Koustenis
Advanced Automotive Machine
Waldorf Md



[This message has been edited by BillK (edited 05-02-99).]
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post #7 of 12 (permalink) Old May 2nd, 99, 03:06 PM Thread Starter
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Thanks a lot for the input.

I already sprayed Gumout on the choke and down the side where the lever comes up. I think if it turns out to be choke, I may just get a manual choke installed. I figure it's better off if I just control it myself than if I have to fix a million things and hope they stay working. It's an 86 and it's got like 140,000 miles on it.

Where exactly is the throttle shaft? I don't know that much about carburetors and don't want to take the thing apart unless I absolutely have to.

As far as vacuum leaks, I don't think it's that, unless it seals itself as the engine warms up or some crazy stuff like that. The idle is fine once I can get the car running.

Thanks again.
Mark
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post #8 of 12 (permalink) Old May 3rd, 99, 02:18 PM
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Mark,
With 148 K miles, the throttle shaft is almost certaintly loose. This is the actual shaft that the throttle cable attaches to. If you look at the shaft where it goes through the carburetor base and try to move it foward and back you will see where it has worn the hole in the carb oblong. This allows the throttle "butterflies" to hang up as they close, keeping them open enough to speed up the idle. This is going to require you finding someone with the tools to install bushings in the carb base, or replace the carb. If you can stand being without the car for a week or so, take the carb off, send it to the Carburetor Shop in California and have them rebuild it. They specialize in Q-jets and will make it like new. Dont waste your time with the manual choke as it will probably not fix the problem anyway.

------------------
Bill Koustenis
Advanced Automotive Machine
Waldorf Md



[This message has been edited by BillK (edited 05-03-99).]
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post #9 of 12 (permalink) Old May 3rd, 99, 03:29 PM Thread Starter
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Thanks for your help.

I probably won't be able to take the carburetor off until this summer, when I get out of school, but I was considering getting the carb rebuilt anyway. Can you give me the address or number of this place in Cali?

And is there anything else about the startup sequence that would affect idle OTHER than the carb or a vacuum leak? I just want to make sure I cover everything before I get the carb restored.

Thanks a lot, it really helps to talk to an expert about these things.

Mark
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post #10 of 12 (permalink) Old May 3rd, 99, 05:32 PM Thread Starter
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I'm sorry to keep asking questions about this. I'm not doubting your diagnosis, but since I was born I've been plagued with a desire to understand everything.

If it IS the throttle shaft, then how does finally getting the engine warmed up correct the problem? After I fool with the Gumout, etc, and get it running right, I have NO problem while driving and can easily restart the car after even 5 or 6 hours. That's why I originally thought it was the choke.

Is it possible that the throttle shaft is just sticking and requires some kind of cleaning or lubrication?

Also, what kind of tools do you need to rebuild a carburetor yourself? Is it something you can get a book on and do yourself or do you REALLY need to be intimate with the carb?
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post #11 of 12 (permalink) Old May 4th, 99, 02:05 PM
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Mark,
It could possibly be something else, it gets real difficult to diagnose these types of problems without having the carb in fornt of you. Q-jets are not very hard at all to work on if you are pretty good mechanically and have some patience. I would however recommend getting a book on them first. I think Peterson prints one. I have it at the shop and still look at it after 30 years of messing with them.

------------------
Bill Koustenis
Advanced Automotive Machine
Waldorf Md

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post #12 of 12 (permalink) Old May 4th, 99, 08:57 PM Thread Starter
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Thanks again. I looked last night and I could see where the throttle shaft had worn the hole down. I think I've got a smatter of all the usual Q-Jet problems. However I also examined the linkage and hosed everything that looked like it moved with carb cleaner...the engine had never started better since I bought it.

Today it didn't even need to choke, but I think that's cuz it was hot out. A rebuild may be in the future, but with my current financial and time demands I'll have to hold out a little longer. Do you think it might be beneficial to lubricate the linkage joints with WD-40 or some other lubricant?

Thanks again.
Mark
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