High idle speed and no more surging after intake rebuild

[Bitsyncmaster]

Is it possible the idle ECU is flaking out?

It's possible but usually ECU failures are the driver transistors from a shorted idle motor. But your running out of things to check so if you can get another owner who will let you borrow his ECU than that would confirm or eliminate that problem.

[MrChocky]

It's possible but usually ECU failures are the driver transistors from a shorted idle motor. But your running out of things to check so if you can get another owner who will let you borrow his ECU than that would confirm or eliminate that problem.

I have one spare. If you end up wanting to send to Dave for upgrade to his, we can work that out.

[82DMC12]

I have one spare. If you end up wanting to send to Dave for upgrade to his, we can work that out.

Thanks! Might end up taking you up on it. I'd appreciate being able to simply borrow it for a day just to swap out and check, if it comes to that. I'm definitely running out of things to check. I don't really want to spend $100+ on a smoke machine I'll probably never use again.

A couple things I could try -

1) Remove the vacuum line from the passenger side of the intake and plug the barb. Maybe there's a vacuum leak upstream from there.
2) Swap Idle ECU for known good ECU
3) Swap throttle body for known good throttle body
4) Keep working on the linkage. I guess I could remove the wires from the idle speed switch and join them, then back out the idle stop screw 100% and just hold the throttle closed. See if that results in the right idle speed. If it does, then I know my problem is related to the butterflies sticking or some kind of weird linkage binding or some crazy thing in the spool that was OK before but now isn't.

[82DMC12]

Thanks! Might end up taking you up on it. I'd appreciate being able to simply borrow it for a day just to swap out and check, if it comes to that. I'm definitely running out of things to check. I don't really want to spend $100+ on a smoke machine I'll probably never use again.

A couple things I could try -

1) Remove the vacuum line from the passenger side of the intake and plug the barb. Maybe there's a vacuum leak upstream from there.
2) Swap Idle ECU for known good ECU
3) Swap throttle body for known good throttle body
4) Keep working on the linkage. I guess I could remove the wires from the idle speed switch and join them, then back out the idle stop screw 100% and just hold the throttle closed. See if that results in the right idle speed. If it does, then I know my problem is related to the butterflies sticking or some kind of weird linkage binding or some crazy thing in the spool that was OK before but now isn't.

Hey everyone,

I don't like leaving threads that I started "open" so I thought I'd provide an update.

1) I was able to confirm my vacuum coming off the passenger side barb is tight - I used a Mityvac to pull a vacuum and it held. I removed the vacuum hose from the driver side barb and did the same - also holding. So I knew I wasn't leaking vacuum through a hose or fitting.

2) Performed enough tests of the Idle ECU to effectively rule it out with 99% certainty

3) Didn't swap the throttle body because I kept working on the linkage. What seemed to help was to disconnect the linkage rod from the throttle spool, back out both idle stop screws (the curb idle screw and the throttle microswitch screw) and push down on the throttle arm so that the throttle was seriously closed while I slowly turned the curb screw back in until it just started to lift. Then I turned the microswitch screw in until the switch engaged and gave it another 3/4 turn. Then, on the rod, I loosened both jamb nuts so that I could turn the rod to lengthen or shorten the rod rather than loosening only the spool-side nut and turning the ball end a complete revolution either way. By turning the rod, I got much finer adjustment available and basically just shortened the rod until I couldn't shorten it anymore with my fingertips while the rod was attached at both ends. That way the spool was holding the throttle closed in rest position.

So now I'm sitting around 850 RPM maximum at hot idle but sometimes it drops to 750. I'm so close and I'll do a bit more tweaking but the linkage really is touchy. At least I was able to go for a nice drive this weekend and enjoy the car - the engine is running super smooth again! Also no more "dieseling" when I shut down.

I also replaced the rubber throttle body spacer with a DPI billet aluminum spacer - it has a larger diameter and doesn't restrict the air flow. Call me nuts but I feel like I have a bit more power in the mid-range now.

If I come up with any more advice I'll be back here to share it.

[David T]

Based on what you just did, your Quadrant Link (the rod that connects the throttle arm to the throttle spool) is worn. The ball ends wear and develop play so when you release the throttle, it doesn't go all the way closed. That rod (link) has left and right hand threads so it can be finely adjusted but once you get wear you can only adjust the play out in one direction. You might notice a slight lack of response when you step on the pedal, that's the play (looseness) you are taking out before you move the throttle arm. There are 3 springs in the throttle linkage. 2 in the throttle spool and one in the throttle body. After 30 + years the grease and oil that was originally in there turns to glue. If you want the throttle to operate smoothly it should all be taken apart, cleaned and relubricated. It also wouldn't hurt to lubricate the throttle cable as per the recall with some anti-freeze. The way I do it, I disconnect the cable at the throttle spool, attach a piece of hose that slips over the end, and secure it with a hose clamp. Fill the hose with anti-freeze and then hook an air line to the end. Pressurize the cable till you see anti-freeze come out the end by the pedal.
For the throttle body, there are 2 set screws. One is the stop for the throttle arm and should not ever need to be adjusted and the other is for the idle switch. Do not over adjust it, it should just trip that micro and not push too far after that. Check that the decel springs are holding the valve plates closed. If the motor ever backfired it fried those springs and they lose the ability to hold those valves shut. Replace them with some springs from retractable pens. Cut them to fit. Vacuum leaks are the bane of trying to get the motor to run and idle correctly. Any leaks take away from the idle motor's ability to control the idle so make sure you have fixed ALL of the vacuum leaks. Best way to find them is with a smoke machine. Some common things that leak are the injector seals and the "O" ring for the air pipe that goes to the idle motor on the bottom of the mixture unit.

[DMC-Ron]

It also wouldn't hurt to lubricate the throttle cable as per the recall with some anti-freeze. The way I do it, I disconnect the cable at the throttle spool, attach a piece of hose that slips over the end, and secure it with a hose clamp. Fill the hose with anti-freeze and then hook an air line to the end. Pressurize the cable till you see anti-freeze come out the end by the pedal.

David,
What are you using for the anti-freeze (anti-seize) lubricant. Could you post a link or provide the name?

Ron

[David T]

David,
What are you using for the anti-freeze (anti-seize) lubricant. Could you post a link or provide the name?

Ron

The good ole green stuff, aka Prestone, mixed 50/50 with water as per the throttle recall.

[DrWin]

So I basically want to ask a related question: Anyone wants to chance a guess as to what is going on with my engine after my VOD rebuild?

1. Engine cold, ambient temp below <15*C => Engine starts, hunts for 5 secs, goes to 600-700rpms and runs steady for 30 secs. Dwell meter steady at 22* (8-cyl scale).
2. Engine warm (?), ambient temp < 15*C => Sudden change to 900rpms, runs steady for a few minutes. Dwell meter steady at 22* (8-cyl scale).
3. Engine warmer (?), ambient < 15*C => Gradually changes up to 1100rpms, runs steady. Dwell meter has started to move between 23* and 17* (8-cyl scale).

My impression is that the change from open to closed loop on the idle speed ECU and the changes in rpms weren't coincidental, that is the timing wasn't a match.
I sounded more like the changes weren't syncronised, like it was several different things that actvated in sequence. (Makes sense?)

Also, I just tested what happens when I hit the gas - It revs up to whatever and then drops down to 775rpm OR stays at 1100 rpms, seemingly at random. This strongly suggests that the throttlecable is sticking, right?

[SS Spoiler]

same problem, idle creeps up as it warms up.
but if I turn my lights on and off it drops to normal.
ideas?....

[David T]

Reread post # 25. Either you have play in the linkage or it is sticking.