I'm having trouble getting the idle speed correct on my '79.

While the car is running, standing still with the trans in DRIVE, engine is idling around 900.

While the car is running, standing still with the trans in NUTERAL, engine is idling around 1600. This seems way too high to me. But if I reduce it, then the idle is too low with the trans in Drive.

I don't know what to do about it.

Suggestions?

What are your engine's idle speeds?

Thanks!

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-Adam Wartell
NCM Lifetime Member #1222
Founder: C3 Vette Registry 
C4 Vette Registry, C6 Vette Registry

My first Vette, now owned by JB79:

My 79 does the same or very similar thing. After I run the car (let it warm up) for 3-5 minutes, the idle speed drops and everything is fine. I asked my mechanic about the phenomenon and he mentioned that it was not a-typical for carbureted engines.

Does yours settle down after it warms up? Mine starts out at about 1700-2000 RPMs and then drops to about 900 when it warms up. It sounds like there's a small plane in the garage in the morning when I first start it up.

I do have a new crate motor which would lead me to believe that it is a carburetor thing. If the phenomenon is new, perhaps it has something to do with the recent drop in temperature in your neck of the woods.

Andy

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1979 Corvette. 330HP 350ci Chevy Vortec. Dynomax ceramacoat headers. Holley 650 4bbl. 3 speed automatic 350 turbo tranny w/ shift kit & torque converter dyno'd @ 864 ft.lbs |IMG|http://www.rogerscorvette.com/free/milligan.jpg|/IMG|

|QUOTE|GTSTMPR said: ...Does yours settle down after it warms up?...|/QUOTE|

I should have specified...this IS after it warms up.
Before it warms up, these numbers are much higher.

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-Adam Wartell
NCM Lifetime Member #1222
Founder: C3 Vette Registry 
C4 Vette Registry, C6 Vette Registry

My first Vette, now owned by JB79:

Sounds like your automatic choke needs to be adjusted,( black round thingy on the passenger side of the carb if it is electric or would look like an 1/8" rod coming up from the manifold to the carb). You could probably adjust the electric one yourself. If it is the other type, get a case of good beer and call George. That doesn't mean you need to bribe him, it will just be nice to have it on hand "just in case" .

The motors manuals that I have stop short of 79 but all say 600 or 700 in drive. The engine should be at running temp. thats to make sure the choke is open, But you should also be sure that the fast idle is not sticking.

|UPDATED|11/14/2002 9:02:29 PM|/UPDATED|


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Go thru all the carb and choke adjustments in order. They are found in various places: Motors manuals, Carb rebuild kits, Doug Roe's Rochester Carbs book, etc.

Mine idles at 750 in park, 550 in drive, a little lower than specified, but that's how I like it.

I can't tell what your particular solution is, there are a bunch of rods and screws that need adjusting, any one or a combination could be causing your problem. Fast idle should start about 1200 in neutral and quickly come down to 900-1000 on the second step. It shouldn't take a stock motor more than a few minutes to be on the low idle step.

Joe

|UPDATED|11/14/2002 10:49:38 PM|/UPDATED|

Mine idles at around 450 in drive and 600 in Neutral, I guess mine is way low, based on everyone elses numbers. This may have changed since the "useless" choke was replaced since I last drove.

Scot

Adam:
According to the Specs package I received from Chevy (and I think you have the '79 L-48 automatic, same as me) dated October 1978 the idle speed should be 500 (in drive). L-82 should be 700 in drive.

Manuals in neutral should be:
L-48 - 700
L-82 - 900

Hope this helps, but it sounds like you might have choke problems.

FWIW, my idle speed needs to be tweaked every fall when they bring in that crappy oxygenated gas and it gets cold so the idle cam doesn't come off all the way easily. I also have to adjust the idle mixture on the Q-jet, not just the idle setting on the throttle. Then in spring I reverse the ritual. The 1970 350/300 TH400 specs from the GM service bulletin are 600 RPM in drive and 750 in neutral. I believe the 4spd idle settings are a bit higher, but I'd have to go look that up to confirm and I'm being lazy right now. ~Juliet

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I HAVE AN 80 L82 WHICH ALSO HAS AN IDLE PROBLEM. I HAVE CHECKED VACUUM HOSES, PCV,AND LOTS OF OTHER THINGS. THIS CAR HAS SAT ALOT THIS LAST YEAR. SHE RUNS GREAT AT FULL CRUISING SPEEDS. FAST IDLES 1200, SLOW WARMUP IDLE SWINGS BETWEEN 500-700 AND I NEED TO KEEP MY FOOT ON THE BRAKE AND GAS AT A LONG STOP LIGHT TO KEEP HER RUNNING. I BROUGHT HER INTO THE SHOP TODAY AND THEY THINK I NEED TO REBUID THE CARB. I'LL LET YOU KNOW IF THIS IS THE TICKET.

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During these colder months, I need a good 3-4 minutes of "foot throttle" just after starting to keep her from stalling. Once warm, my idle is about 700 in park & 600 in gear. I never thought of the oxygenated gas mentioned above. . . but who knows. By the time I get around to adjusting for this, it'll be springtime & I'll have to reset it back!
~ Joe