Need help with my idle speed
Thread Starter
Racer
Joined: Mar 2002
Posts: 406
Likes: 1
From: Maroochydore QLD
Need help with my idle speed
My 79 is bone stock, just fitted a carby kit to the Rochester and it is now running so smooth, however I cant work out the idle, the sticker under the hood says 650 rpm, I hooked up my digital tacho which is new and I suspect very accurate, in neautral it sounds best at about 850rpm, if I set it to 650 rpm it eventually stalls, its just too low. Now at 850 rpm it drops to about 650rpm when I put it in gear (auto), still too low as it idles rough at this speed in gear so I am forced to raise it to about 950 rpm in park so that it idles nicely at about 780rpm in gear but this is too high out of gear.
What gives? Is the torque converter playing up? Do I have other issues like a vacuum leak (I suspect I may have a valley cover leak) Does anyone know how to test for a valley cover leak? I have plugged all vacuum lines (brake, PCV line etc.) for testing and the idle didnt change.
Cheers, Dennis.
What gives? Is the torque converter playing up? Do I have other issues like a vacuum leak (I suspect I may have a valley cover leak) Does anyone know how to test for a valley cover leak? I have plugged all vacuum lines (brake, PCV line etc.) for testing and the idle didnt change.
Cheers, Dennis.
Drifting
Joined: Mar 2011
Posts: 1,886
Likes: 9
Check all the basics, Dennis. Timing, Vacuum advance, etc.
A slight vacuum leak on the intake manifold will definitely make it idle like $%^&. I have heard of people using an unlit propane torch. You open the valve on the torch with the engine running, and pass it near where you suspect the leak. The vacuum will pull in the propane, and you will hear the idle change. Most people just use carb cleaner spray, but that requires cleanup afterward.
A slight vacuum leak on the intake manifold will definitely make it idle like $%^&. I have heard of people using an unlit propane torch. You open the valve on the torch with the engine running, and pass it near where you suspect the leak. The vacuum will pull in the propane, and you will hear the idle change. Most people just use carb cleaner spray, but that requires cleanup afterward.
Last edited by gcusmano74; Mar 27, 2012 at 09:01 AM.
