I have had an issue with what I think is a lean condition. The vette tends to surge a little when running between 1500 and 1800 rpm in second gear. I have an L48 4 spd with 125K miles. The carb and engien are original. The engine has good compression across the board. Plug insulators are white so I am thinking lean. I didn't notice it when I bought the vette but the engine was not running well to start with. The distributor was replaced (weights and pins shot on orginal one), timing chain replaced (original one streched bad), and the carb was rebuilt (throttle shafts worn badly). The place that rebuilt the carb did a poor job at best so I plan to do some work on the carb this winter.

I replaced the PCV valve at the start of the summer thinking this could be it, but made no difference. When I plug off the PCV valve my rpm drops from 635 down to 530. Is this normal? I have sprayed around the intake manifold and carb base with WD40 looking for a leak but could find none. I have plugged off the vac line to the controls and it did not change the idle rpm.

Any ideas? I am going to plug the PCV valve and take it for a run to see if that changes anything.

Thanks

The PCV valve itself is probably not the problem. You might have a lose fitting grommet(in the valve cover), or on the hose for the PCV valve to the carb.
It is normal for the engine rpms to change when you plug the end of the PCV valve. The PCV is designed to pull contaminated vapors from the engine crankcase into the intake, to be burned. This is why you also have a "filter" in the air cleaner assy., from the tube on the valve cover. It allows the PCV to draw the vapors thru the crankcase(basically, a "controlled" vaccuum leak). Otherwise, it would simply create a vaccuum inside the engine.
My bet would be a problem with the carb, and/or the ignition system.

Thanks, I did plug the vac line to the PCV valve and it didn't make a difference. So this winter I am going to go through the carb and see if there is something else going on with it.

Speaking of PVC valves... I had a vent cap on each of my valve covers and a guy working on my engine put a PVC valve in one cover and ran it directly into the base of the carb. It doesn't run any better but I have noticed a reduction in oil consumption. Is this correct place to have the PVC valve connected and if not are there any consequences?

That is the correct routing for the PCV, but it should also have the other "vent cap" removed, and a tube run from there to the air filter housing, to be "legal". Its not a real problem to leave the other vent cap on the other valve cover, tho.