Topic: 428 PI Throttle Return Spring Gremlins

[kkupec02]

I replaced my throttle return spring bracket and spring back to stock over a year ago using Mansfield Restoration parts. I have had no issues. I started the car up yesterday and couldn't get the rpm to go under 20,000 through the pedal. I revved it multiple times but it hung up at 20,000. I went into the engine bay and could reduce the rpm by hand manually returning the linkage to the idle position. Gremlins must have gotten into the car because it makes no sense. The throttle return spring is now loose and flopping in the anchor holes. No tension what so ever. No changes were made. What would have shifted to cause the spring to be loose now? I have it working again through the pedal by putting an aftermarket spring on and cutting it to create the tension needed. But of course, that only masks the problem.

[Bob Gaines]

If one or more of the duel four throttle shafts are hung up so that they/it stay open could be a reason for excess RPM beyond the idle setting and a properly positioned spring bracket and spring to be loose. Another thing could be the duel four linkage has gotten hung up and would result in the same symptom. The gas pedal linkage hung up for some reason  also could cause the same thing. You will have to go through each one of those things to determine which one is the root cause .  Hopefully it will be simple lubrication or smoothing out a rough edge somewhere.

[carlite65]

20,000? new on me here.

[kkupec02]

The weird thing to me is that a new properly tensioned after market spring seems to have fixed the idle problem and it is now returning properly.

[Bob Gaines]

The weird thing to me is that a new properly tensioned after market spring seems to have fixed the idle problem and it is now returning properly.

Good to hear a apparent higher tension spring solved your problem for now. The Mansfield part should have needed no help. I would go through the systems to try and determine the root problem because it might get worse or cause other problems in case of internal carb issues.