72 LT-1 Idle Issue
Thread Starter
Burning Brakes
Joined: Jan 2006
Posts: 1,073
Likes: 331
From: Clear Lake Shores Texas
2016 C3 of Year Finalist
72 LT-1 Idle Issue
My 72 LT-1, all stock with the exception of a Holley Street Avenger carb, used to idle at a steady 900 RPM, per specs. Now, after the engine is warm, the idle drops to down to be about 500 RPM when coming to a stop and then slowly climbs back to a slightly rough 850-900 RPM idle. It has also become harder to start when it is warm, almost like it is slightly flooded. However, there is no evidence of gas dripping into the carb after a hot shutdown. The car runs well other than the idle issue. Anyone have any ideas?
Thanks
Thanks
Racer
Joined: Jun 2016
Posts: 336
Likes: 29
From: Il.
Check the EGR valve it opens when the engine gets to temp and if it is leaking vac that could cause the bad idle.Get the engine to temp so it starts running bad and take the vac line from the carb to the EGR temp sensor valve at the front of the engine and pull it off the carb. Put you're finger over the the carb port and see if the engine starts to idle right.
Is my vette stock?? HAHA
Joined: Oct 2015
Posts: 20,216
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From: Im not allowed to tell you
2020 C3 of the Year Finalist - Modified
2020 Corvette of the Year Finalist (performance mods)
2019 C3 of Year Winner (performance mods)
2016 C3 of Year Finalist
Did you drive it this summer in hot ambient air conditions with no problem?. Reason I ask is my 68 has a 72lt1 motor and I had a perculation problem in the spring as the outside air temp rose, my problem got worse. Wooden spacer, moving the gas line, using a fuel pressure regulator solved my problem.
Sparkiy77es assessment sounds like a good start otherwise. Either that or you got some bad gas and it dirtied your idle circuit in your carb. If the egr doesnt work try pulling the idle mixture screws and blowing low pressure air through the circuit. The edelbrock tech online suggested that in a vid on my carb. Shouldn't hurt yours
Sparkiy77es assessment sounds like a good start otherwise. Either that or you got some bad gas and it dirtied your idle circuit in your carb. If the egr doesnt work try pulling the idle mixture screws and blowing low pressure air through the circuit. The edelbrock tech online suggested that in a vid on my carb. Shouldn't hurt yours
Last edited by Rescue Rogers; Oct 17, 2016 at 08:41 AM.
Safety Car
Joined: Aug 2000
Posts: 3,711
Likes: 43
From: San Antonio TX
A '72 (any engine) does not have EGR. A drifting idle is usually an sign of a carburetor out of adjustment or in need of a cleaning. A cheap vacuum gauge is a very useful tool when it comes to collecting engine performance data. I suggest you get one since diagnosing a problem without data is just shooting in the dark.
Melting Slicks
Joined: Feb 2006
Posts: 3,105
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From: Sunrise FL
Thread Starter
Burning Brakes
Joined: Jan 2006
Posts: 1,073
Likes: 331
From: Clear Lake Shores Texas
2016 C3 of Year Finalist
Thanks for all of the suggestions. I actually have a vacuum gauge but didnt think it would be helpful in this instance since the problem occurred only under certain driving conditions and not when idling in the garage. I had fuel percolation issues with the original carb as well as other issues that could not be resolved which is why I run the Street Avenger.
While I had checked the fuel level on the primary side I had not on the secondary side and when I looked at that today I found it was quite high. I couldn't adjust it and had to change out the needle and seat. That appears to have fixed it. Thanks again for the help.
While I had checked the fuel level on the primary side I had not on the secondary side and when I looked at that today I found it was quite high. I couldn't adjust it and had to change out the needle and seat. That appears to have fixed it. Thanks again for the help.
