inconsistant idle
Thread Starter
Heel & Toe
Joined: Aug 2013
Posts: 17
Likes: 0
From: romoland california
inconsistant idle
I have been working through may problems, and are close to the end in getting my vette ruing great.
after chaning intake manifold and carb back to original. I have it running well and tuned up based on ear and timing lights, air fuel ratio tester etc.
last problem.
when I set the idle in neutral, then put it in gear the idel is too low. when I increase it in drive, then put it in neutral , it idles too high.
I can't get it to idle at the correct speed for both conditions (neutral and drive).
any suggestions where to look or try next?
Vet69
after chaning intake manifold and carb back to original. I have it running well and tuned up based on ear and timing lights, air fuel ratio tester etc.
last problem.
when I set the idle in neutral, then put it in gear the idel is too low. when I increase it in drive, then put it in neutral , it idles too high.
I can't get it to idle at the correct speed for both conditions (neutral and drive).
any suggestions where to look or try next?
Vet69
Le Mans Master
Joined: Oct 2006
Posts: 7,123
Likes: 433
From: Gladstone MO
C3 of Year Finalist (appearance mods) 2019
I don't know the exact specs for your car, but it used to be around 650 in drive. They jump to about 750 in park or neutral. That's memory so subject to error.
Thread Starter
Heel & Toe
Joined: Aug 2013
Posts: 17
Likes: 0
From: romoland california
But I set it at 550 rpm in drive, then it goes to 1100 rpm in neutral.
any ideas why such a large difference when under load or not.
it is a 350/300 hp with an automatic trans.
Le Mans Master
Joined: Apr 2011
Posts: 6,284
Likes: 1,170
From: Hermosa
Most likely reason is low initial timing or loss of vacuum at low rpm causes vac timing to drop out if your using manifold vacuum source. Try increasing your initial timing.
Have you set the idle mixture screws for highest rpm at idle?
Have you set the idle mixture screws for highest rpm at idle?
Last edited by REELAV8R; Sep 28, 2013 at 10:20 AM.
Le Mans Master
Joined: Oct 2006
Posts: 7,123
Likes: 433
From: Gladstone MO
C3 of Year Finalist (appearance mods) 2019
Also make sure the fast idle cam is not holding the throttle open- and the choke is all the way open/off. Check the advance springs in the distributor too. If they are missing or too light the RPM change could be changing the advance.
Thread Starter
Heel & Toe
Joined: Aug 2013
Posts: 17
Likes: 0
From: romoland california
timing at idle is at 12 degree BTDC
I had the idle screws adjusted well, tested with fuel/air mixture right on.
a I was going check the vacuum today by disconnecting vacuum lines from manifold to see if it made a difference.
Le Mans Master
Joined: Apr 2011
Posts: 6,284
Likes: 1,170
From: Hermosa
Other causes could be a vacuum leak. I've never set mixture screws with an a/f gauge so no experience in tat area, but if the idle rpm changes when you either screw them in or out that is an indication that it was not optimal where they were.
Ignition timing may not be optimal at factory setting either.
This a recent development? Any changes to the engine recently?
Ignition timing may not be optimal at factory setting either.
This a recent development? Any changes to the engine recently?
Thread Starter
Heel & Toe
Joined: Aug 2013
Posts: 17
Likes: 0
From: romoland california
Other causes could be a vacuum leak. I've never set mixture screws with an a/f gauge so no experience in tat area, but if the idle rpm changes when you either screw them in or out that is an indication that it was not optimal where they were.
Ignition timing may not be optimal at factory setting either.
This a recent development? Any changes to the engine recently?
Ignition timing may not be optimal at factory setting either.
This a recent development? Any changes to the engine recently?
now it is back to stock, so I tuned it (think I have mixture and timing right). so I was trying to set the idle.
I ran into another problem or two today, will check out the vacuum possibility when I get back at it.
Vet69
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Safety Car
Joined: Jan 2009
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From: anchorage ak
Other causes could be a vacuum leak. I've never set mixture screws with an a/f gauge so no experience in tat area, but if the idle rpm changes when you either screw them in or out that is an indication that it was not optimal where they were.
Ignition timing may not be optimal at factory setting either.
This a recent development? Any changes to the engine recently?
Ignition timing may not be optimal at factory setting either.
This a recent development? Any changes to the engine recently?