Another high idle thread - how-to on butterfly plate springs?

[jawn101]

Hey all. So, this issue has been plaguing me for years and I've finally decided it's time to tackle it.

Same old story. Car turns over perfectly every time, initially the idle is a smooth 750.

After some warm-up or driving, the idle will raise to 900-1000. Blipping the throttle doesn't help it. Shutting the engine off entirely and restarting it, however, does. If I get out and push the throttle arm closed in this state, it doesn't change anything.

This leads me to believe that it's not mechanical, to do with the quadrant arm, throttle spool, etc at this point, but rather perhaps vacuum related. All of my vacuum hoses are new and silicone (and have been recently done, without helping this issue).

I remember ages ago Elvis was quite hot on the notion of cleaning and maintaining the decel valves on the butterfly plates. I know that these might stick slightly and cause a higher idle.

My theory right now is that it makes sense that shutting the engine off entirely and restarting it would remove any air backpressure. This in turn is allowing them to close fully and resetting my timer on the high idle for a bit.

But now I can't find that thread he created about maintaining those springs. Getting the throttle body out is a fairly quick job, but I can't remember if he was advocating for new springs (and if so where to get them) or a good way to check/revitalize the existing ones.

Anyone have a link, a guide, or any other advice? My theory may also make no sense and I'm open to that. But this engine has been overhauled several times and all the new plugs, wires, injectors, fuel lines, water/vacuum hoses and gaskets in the world have not changed this one lingering issue.

[Ron]

First, double check that the vacuum routing going to the vacuum solenoid is correct. If the two are backwards, it will act normal until you rev the engine, then hold the advance a little high until you shut the engine off because it can't vent correctly.

[jawn101]

First, double check that the vacuum routing going to the vacuum solenoid is correct. If the two are backwards, it will act normal until you rev the engine, then hold the advance a little high until you shut the engine off because it can't vent correctly.

Oooh, interesting. I hate that solenoid on the diagram because it's like...basically impossible to tell

Will do that now. It should only take an hour

[jawn101]

OK, that was easier than I remembered it being. The confusing part of the diagram I was remembering is actually the CSV tube.

Solenoid is hooked up correctly.

[Bitsyncmaster]

Everything but the shutting the engine off fixes it sounds like bad deceleration springs. So how long does that shutting off fix it? The springs should only open after you release the throttle quickly.

[jawn101]

Everything but the shutting the engine off fixes it sounds like bad deceleration springs. So how long does that shutting off fix it? The springs should only open after you release the throttle quickly.

Uh, not very long. A minute or two maybe?

[jawn101]

Hmm. Then what else could it be? I had a friend suggest that the idle motor might be sticking, I haven’t investigated that yet.

[David T]

One possibility is that the throttle arm is not being returned ALL the way to the idle stop position. That can happen if you develop a lot of play (looseness) in the rod ends of the quadrant link or the throttle cable or throttle spool is sticking and not moving smoothly and easily. Verify that the idle switch is getting "set" when you release the gas pedal. If anyone messed with the idle stop screw and/or the idle switch adjustment the throttle plates may not be fully closed and if the air screws are not closed air can be bypassing through them. Just a few more things to check.

[jawn101]

One possibility is that the throttle arm is not being returned ALL the way to the idle stop position. That can happen if you develop a lot of play (looseness) in the rod ends of the quadrant link or the throttle cable or throttle spool is sticking and not moving smoothly and easily. Verify that the idle switch is getting "set" when you release the gas pedal. If anyone messed with the idle stop screw and/or the idle switch adjustment the throttle plates may not be fully closed and if the air screws are not closed air can be bypassing through them. Just a few more things to check.

Thanks, but as I mentioned the quadrant arm and throttle spool seem mechanically correct, and the idle switch is engaged. Both screws have their factory paint marks intact and nobody's touched them. Brass screws are all closed tight. Pushing the throttle arm "more closed" when the idle raises while warm doesn't change anything.

[David T]

Well, you are getting "false air" leaking in somewhere then. Either you find it visually or you do a smoke test to find the leak. A missing gasket, a leaky hose, something. On one car I found a leak, it was on the right side intake runner, front surface, the seal plug was squished because someone used too long a bolt on the ground connection and it bent the seal plug. Vacuum leaks can be difficult to find. On another car the "O" ring was missing on the cold start valve. Often the injector seals leak. Also common for the tube to the idle motor "O" ring on the bottom of the mixture unit. Point is you have to look for the unusual.