RPM's do not return to Idle

[Steve Gallegos]

When I step on the gas in neutral or any gear then back off, the RPMs drop to about 1500 instead of 900. Sometime it will slowly go back to 900, other times I have to rev the engine to get it to drop. I checked my throttle line and it works fine. Iam running a 351W with Edelbrock EFI with MSD electronics. I was told by Edelbrock that the problem could be my coil. Any suggestion

[twobjshelbys]

Mine does it too. I am going to try a return spring on the accelerator.

[Excaliber]

That happened to one of my two carbs recently, steadily got worse to the point where I had to "blip" the throttle briskly to get the idle to return to normal. Tried a heavier spring, re-routed the spring(s), nothing helped. Finally took off the carb and inspected on the bench. The throttle plate action is just a hair sticky, it won't return to full closed position without a slight push. The return spring was side loading it in such a way as to exasperate the condition. I keep an identical spare carb so I replaced the sticky one with my spare one. Idle is once again perfect. Which now leaves me with a defective spare carb.

I'm not sure what's going on with the throttle plates on the bad one. I tried WD-40, carb cleaner, etc, it still hangs up just a fraction. That carb is only a couple of months old, no carbon or nasty stuff on it. I suspect it's just flat out defective out of the box. Bummer....

[dcdoug]

You haven't been playing with distributor springs have you? If the springs are too light they can lose a bit of their tension and the advance doesn't return to zero. Easy to check with a timing light.

[RET_COP]

If your springs are pulling the throttle blades closed in the same direction you throttle is pulling the throttle blades open there is a lot of side load on the shaft which can cause misalignment and binding. [your throttle open action being on top and the spring closing action being on the bottom]

Try putting the springs on the opposite side of the throttle action [pulling from different directions] which will balance out the load and maybe stop some misalignment and binding.
Lou

[olddog]

From your description, it does sound like the throttle body is sticking and not going closed as suggested by others.

It could also be the idle air control valve (IAC) sticking open.

If the EFI is controlling the spark, there are no springs to check.

With it idling high, you can try closing the throttle by hand to see it that is it. You could also try unplugging the IAC, but if it is mechanically stuck unplugging it will do nothing.

Most IAC are easy to take off and clean up with choke cleaner. I never worked on your system.

I am shocked that the help line suggested the coil. It sounds totally off the wall to me. I see no way on this earth that a failing coil could cause a high idle.