Hello i have a 1979 corvette with the following modifications a 600 cfm holley car, a high rise edlebrock intake, and side pipes. I am having trouble with the idle only when in drive and in reverse never in park or neutral though. The idle problem only happens when the engine is warm never when its cold. When the engine gets to temperature the idle when at a stop while in park becomes erratic, it idles fine for a few seconds then jumps up one or two hundred rpm's and makes it seem like i have tapped the accelerator very slightly, I know this is going to sound stupid but it sounds like vvvvvvvvvv vmmmmmmm vvvvvvvvv where the vvvvvv is the normal idling as it should, and the vmmm is the idle jumping up one or two hundred rpm's. the car also hesitates when the engine is warm the car wants to stall and choke out like the rpm's go really low and if i don't press the gas the car will stall, but will start right back up if i try to start it.
I have already tried seafoam and changing the air filter, but other than that nothing so far, the air filter i changed to was the muscle car cold air intake by spectre with the flex tubing, i am not sure if i should attempt to change the air filter again or what??? because a mechanic told me a simple air filter replacement would fix the problem!
thank you in advance for any help on this!

 

Sounds like your mechanic doesn't necessarily know what he is talking about.

This link has a timing article written by Lars. He is one of the forum's carb and timing experts.

http://lbfun.com/Corvette/Tech/vettetech.html Look in the Timing and Vacuum Advance section for Timing for Peak Performance

Sounds like it could be a timing or carb issue. Little more info may help. I'm assuming a 350. What is your cold idle (with choke on) and what is your curb idle (once hot)?

You can email him at V8FastCars@msn.com and he will send you his latest version of the timing paper and one on how to tune your carb. You will be amazed how much better it runs when timing is correct. Mine used to stall at stop lights when in drive too.

 

my engine i believe is a 350 or a 327 not sure becasue the stamp on the block codes for both but i have been told its a 350 my car idle at 5 or 600 rpm when in drive but when in park it idles at 1000 this is with my choke all the way off, when it is all the way on its at 1300 when its in park and when in drive i believe its at like 600 definitely not more than 700 rpm, and thank you for your quick reply ill check the link out now

 

funny you post this, my car has developed same exact warm only, drive(gear) only, idling. I was gonna check my plugs tomorrow. I changed them a few months ago, but it acts like one is kinda fouled a little. I also checked for some air intake leaks, I found something. tomorrow when I drive it to work for a little while, I'll know if it was a vacuum leak.

 

Hey could you let me know if it was a vacuum leak i was also suspecting this and/ or my vacuum advance like scottw suggested, i also changed my spark plugs a few months ago maybe it is that, please let me know what you find out! thanks

 

Make sure your choke is pulling off after it warms up

 

went ahead and just checked plugs before driving since engine is cool. they were all fine as I suspected since guy I bought car from said engine is a crate with only about 27K miles. I don't think my issue is ignition related, distributor and all of its components are only a few months old and the wires are the fancier MSD wires, they also being only a few months. leaving now to work some, we'll see how it idles after it warms up

 

yeah, I'm good now, at least what driving I did do. rtv where the plate bolts onto manifold for the 2 lines that connect choke and back side of carb. edlebrock

 

Make sure your vacuum advance is connected to manifold (not ported) vacuum. Then get yourself a timing light and set up your ignition timing according to Lars' specs. If that doesn't solve your problem, I would start looking for vacuum leaks.