Rising Idle - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Hard Luck · 03-22-2012, 01:09 AM

Out driving the CST and as the day pressed on, idle speed increased. I will try to be as specific as possible.

327 with a slight cam, turbo 350, HEI, Edelbrock manifold with their Q-jet, and long tube headers. Outside temps were steady at about 40. Ran a bunch of errands, stop and start with the average speeds around 30 to 40mph. Total time was about 2 hours. Engine temps at a constant 180 degrees.

Fresh tune up, recent oil change, new belts and hoses, coolant system flush with new thermostat.

Started the day with an idle of 800 in neutral and in gear about 500. Little bit of lope, does not seem like it can go any lower in gear. After a few stops the unladen idle went up to 1000 but in gear was still 500. Runs and drives just fine. A few more stops and idle rises to around 1200 but in gear is still 500 and still runs fine. No visual clues as to what is going on.

Any ideas?

gcburdic · 03-23-2012, 10:21 PM

ttt

soxplayer · 03-23-2012, 11:38 PM

Get out the WD 40 and spray around the carburetor looking for a vacuum leak. The 500 in gear wont rise with a leak as the engine would be running lean and not make any more power. If it is a leak and it gets bad enough your truck will stall in gear but idle really fast.

Autoblueprint · 03-24-2012, 12:37 PM

Check the action of the choke spring. The carb choke plate should be fully open when the engine is at operating temp. You will have to take the air cleaner top off each time you stop while running errands to see if the plate is fully open. If it is not, then the choke either needs to be adjusted or replaced.

03-22-2012, 01:09 AM	#1
Hard Luck I've got grease on my mind. Join Date: Sep 2007 Location: Oly, Wa Posts: 481	Rising Idle Out driving the CST and as the day pressed on, idle speed increased. I will try to be as specific as possible. 327 with a slight cam, turbo 350, HEI, Edelbrock manifold with their Q-jet, and long tube headers. Outside temps were steady at about 40. Ran a bunch of errands, stop and start with the average speeds around 30 to 40mph. Total time was about 2 hours. Engine temps at a constant 180 degrees. Fresh tune up, recent oil change, new belts and hoses, coolant system flush with new thermostat. Started the day with an idle of 800 in neutral and in gear about 500. Little bit of lope, does not seem like it can go any lower in gear. After a few stops the unladen idle went up to 1000 but in gear was still 500. Runs and drives just fine. A few more stops and idle rises to around 1200 but in gear is still 500 and still runs fine. No visual clues as to what is going on. Any ideas?

03-23-2012, 10:21 PM	#2
gcburdic Restoration Virgin! Join Date: Jan 2008 Location: Huntersville, NC Posts: 8,298	Re: Rising Idle ttt __________________ Geoff with a G 1968 Chevy C10 SWB The Mistress 1972 Custom Deluxe C20 Suburban A Suburban Named Isabella 1966 Ford Mustang Mama's High School Graduation Present

03-23-2012, 11:38 PM	#3
soxplayer Registered User Join Date: Jun 2009 Location: Forest City IA Posts: 56	Re: Rising Idle Get out the WD 40 and spray around the carburetor looking for a vacuum leak. The 500 in gear wont rise with a leak as the engine would be running lean and not make any more power. If it is a leak and it gets bad enough your truck will stall in gear but idle really fast.

03-24-2012, 12:37 PM	#4
Autoblueprint Registered User Join Date: Mar 2011 Location: Los Angeles, CA Posts: 152	Re: Rising Idle Check the action of the choke spring. The carb choke plate should be fully open when the engine is at operating temp. You will have to take the air cleaner top off each time you stop while running errands to see if the plate is fully open. If it is not, then the choke either needs to be adjusted or replaced. __________________ John Harlowe 1971 CHEVROLET C-10 FLEETSIDE LOWERED



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