Further idle diagnosis....

[Roadster]

Originally Posted by Paul Workman

Ya gonna have to TEST your theories. Can't assume anything; only trust what you VERIFY!

PS:

Because the vacuum pump does shut off, and you're not reporting any codes/secondary issues, the check valve to the plenum IS working. Your Idle problem is NOT coming from the SPT system.

However, besides gaskets, there ARE several other vacuum circuits that could be introducing air into the plenum. You might want to verify the MAP vacuum is not leaking, and then block off the other plenum vacuum circuits, e.g., the purge line, PVC line...see what happens when these other "blank checks" are eliminated...

Will go through all that you have suggested. Makes sense to check all of the vacuum circuits before anything else.

Originally Posted by XfireZ51

Take a strip of paper and stick it between the primary throttle plate and bore. Pull it through. Is there any drag? Do it also after opening the throttle.

I will try the paper test.

Originally Posted by tpepmeie

Do I understand right that the high idle occurs after you've been into the throttle a good bit? I thought I saw that earlier somewhere in this thread. If that is the primary symptom then would point me towards the larger throttle plate mechanism hanging up. The 59 (or. 63mm) bores don't open up under light throttle. It's a progressive linkage.... the small primary plate opens at the first several degrees of throttle position.

Sent from my iPhone using ZR-1 Net Registry

Yes it does occur after I'm into the throttle, but sometimes it's not so much that it would start to bring on secondary operation. And if the larger throttle plate mechanism is hanging up, then why doesn't continue to hang up after a hot restart? I guess I'm having a hard time thinking its the throttle blades. And I know anything is possible.

Originally Posted by conesare2seconds

Fwiw, I had a high idle after the engine was warm. Marc found the throttle blades were hanging up. Had him recondition the throttle body.

That will be the last resort, it's just unusual it happened just like that!!!


Thanks again for all of the replies.....appreciated......
Won't be able to further check things until Sunday. Going out to the 74 again tomorrow, and getting some additional help from a car friend.

[DRM500RUBYZR-1]

Tom,
Just a thought.
You might want to isolate the cruise control and ASR units and controls from the equation to make sure that they are not in any way restricting or affecting the return to idle.
Of the two, the cruise has both vacuum and mechanical interaction.
Perhaps during re-assembly somehow they were jostled.
While vacuum seems to be your gremlin, rule out as much else as is possible.
GL, you will get it!
P.S.
We have a smoke machine if you need to keep looking for vacuum leaks.
Give a call and stop by with some coffee and donuts, and I'll have the guys hook it up.

Marty

[XfireZ51]

This is one of those cases where Occam's Razor applies and yet we keep looking for the more complicated explanations.

[DRM500RUBYZR-1]

Originally Posted by XfireZ51

This is one of those cases where Occam's Razor applies and yet we keep looking for the more complicated explanations.

Those Franciscan's never shaved; They thought it too complex!

Marty

[Hib Halverson]

Couple of observations....

If the IAC counts are zero for a sustained period, given a properly functioning IAC and that the TPS is set correctly, you likely have a vacuum leak somewhere. It can be anywhere in the intake tract, even the TB shafts.

The secondary pump and the port throttle don't affect a problem like this because they are downstream of the TB.

What I'd lke to see if the long term fuel trims for both sides at idle.

I would not use the minimum air adjustment as a bandaid for this problem. In factd, if you've already changed that as a "fix", you've created more of a problem you have solved.

I'd first readjust the throttle stop screw, then start your diagnosis from there.

[Roadster]

I have found the source of the problem, a big thanks to everyone who has replied.
And I stand corrected big time.....the problem is the primary throttle blade.
Here is how the determination came about......
Following the advice from Paul, to check everything out...
Doing the paper test that Dominic suggested...
Giving more thought to what Todd mentioned about the throttle blades...
Also more thought about what conesare2seconds said about his idle...
And also to VetteVet who I spoke to on the phone along with Yun for all of the insight given.....

But is was Marty that put me over the edge......lol when he mentioned the smoke machine, I remembered that there is one out at the garage where the 74 is residing. So I grabbed it today and took it home, a good move.

Marty, thank you sir.....I will still come down and pay you a visit and will gladly bring the coffee and donuts.....and a big thank you for the offer to use your smoke machine, when I read it, the light bulb went off....

Set up the machine, took off the brake booster line on the plenum and hooked up my own configuration of hoses to connect to the open port. Took off the air duct and covered up the opening of the throttle body with a plastic bag. Turned on the machine and there are no leaks coming from under the plenum or any connections on the top of the plenum. But and a very big but is I noticed that the plastic bag over the throttle would expand. I undid the plastic bag and looking directly into the air horn I could now see the steam coming from what I thought was the passenger side throttle plate. Then I realized that there was still an opening that had the be blocked off from inside the air horn. Now doing the test again, the steam is now coming out of the bottom of the primary blade, and nowhere else. Did this test 3 times and the same results. Also did the paper test that Dominic suggested and it did pull through, the first time it was tight, but when I redid the test after moving the throttle, it pulled through a number of times.
So there you have it, I was very hard headed....lol thinking that it cant be the primary throttle blade and that is exactly what it is.....now I know the problem....here are a few pics of the process.....

I had these hoses for years and years without ever using them, today they came in handy for the fog machine...

[Roadster]

my hose configuration...

the plastic bag...

you cant see the steam, but it was coming out the bottom of the primary blade.....

[conesare2seconds]

:thumbs up:

[Roadster]

Originally Posted by Hib Halverson

Couple of observations....

If the IAC counts are zero for a sustained period, given a properly functioning IAC and that the TPS is set correctly, you likely have a vacuum leak somewhere. It can be anywhere in the intake tract, even the TB shafts.

The secondary pump and the port throttle don't affect a problem like this because they are downstream of the TB.

What I'd lke to see if the long term fuel trims for both sides at idle.

I would not use the minimum air adjustment as a bandaid for this problem. In factd, if you've already changed that as a "fix", you've created more of a problem you have solved.

I'd first readjust the throttle stop screw, then start your diagnosis from there.

I have not or attempted to adjust anything. I would imagine that since I found the primary blade to be leaking the fog during the test that I should adjust the throttle stop screw as you mentioned to start with.

I understand that the secondary pump has nothing to do with the problem, but felt I should report everything that I have noticed with the entire system.

I would have to do another Tech 1 test for the latest Fuel Trim info. Previous results are in post #8 unless you have already seen them.

[XfireZ51]

Originally Posted by Hib Halverson

Couple of observations....

If the IAC counts are zero for a sustained period, given a properly functioning IAC and that the TPS is set correctly, you likely have a vacuum leak somewhere. It can be anywhere in the intake tract, even the TB shafts.

The secondary pump and the port throttle don't affect a problem like this because they are downstream of the TB.

What I'd lke to see if the long term fuel trims for both sides at idle.

I would not use the minimum air adjustment as a bandaid for this problem. In factd, if you've already changed that as a "fix", you've created more of a problem you have solved.

I'd first readjust the throttle stop screw, then start your diagnosis from there.

Hib,

Just a point of clarification, but if you are going to "readjust" the throttle stop screw, you would do that only to re-do the min air setting. And that is to adjust for the desired idle w the IAC steps sufficient to allow ECM idle control.