High idle speed and no more surging after intake rebuild

[Bitsyncmaster]

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

Back off your curb idle. If it's all the way backed out then probably you deceleration springs could be bad. Also if you get ignition advance at idle that is another cause. You can test that by pulling the advance hose going to the distributor.

[82DMC12]

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

Not sure what the lights have to do with it, but I'm OP and I had the same problem with idle slowly creeping up as it warms up. The problem was my linkage rod wasn't short enough to keep the throttle plates 100% closed. I had better luck adjusting it by loosening both lock nuts and turning the rod shorter rather than trying to turn just one end shorter. I was able to make finer adjustments that way. I'm not convinced I have it totally perfect (yet) but that did stop the idle from slowly increasing. I've been swamped with work and a 5-month old boy, plus the weather sucks this spring so far, so I haven't had as much time to tinker as I would like.

[Ron]

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?

For the first part- When it is <15°C, the dwell should be 50-60° = 25-30° on 8-cyl scale, steady. Your's is 3° below the minimum. Given that, 1. and 2. above makes sense. And for 3., it is dead on (swinging about 40° = 20° on 8-cyl scale. You might try adjusting it a tad (richer, iirc), which may bring the cold dwell up and make the warm dwell swing wider (10° instead of 6°, about 20° 8 cyl scale. (...maybe not ;-).

The change at .2 could just be the WUR/CPR changing the control pressure (until it reaches 40°C = 104°F).

For the last part- I agree that the linkage is at least playing a part when it stays at 1000 RPM.

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Looks like we are getting too many cars/issues for one thread...

[DrWin]

For the first part- When it is <15°C, the dwell should be 50-60° = 25-30° on 8-cyl scale, steady. Your's is 3° below the minimum. Given that, 1. and 2. above makes sense. And for 3., it is dead on (swinging about 40° = 20° on 8-cyl scale. You might try adjusting it a tad (richer, iirc), which may bring the cold dwell up and make the warm dwell swing wider (10° instead of 6°, about 20° 8 cyl scale. (...maybe not ;-).

The change at .2 could just be the WUR/CPR changing the control pressure (until it reaches 40°C = 104°F).

For the last part- I agree that the linkage is at least playing a part when it stays at 1000 RPM.

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Looks like we are getting too many cars/issues for one thread...

Either that or we are getting enough cars for a great discussion/techsession.

So - yeah… I looked into the throttle cable/body area and can tell that something is binding somewhere, b/c the throttle doesn’t automatically reset to nil after I release the throttle pedal and/or cable (if pulling from the engine bay).

When I manually push it to nil, rpms drops to 700-750 ish and stays steady (if a little rough).

This also seems to suggest that the idle creep up I was experiencing earlier is because the throttle spool doesn’t rotate far enough back to activate the idle speed microswitch, which causes opening the vacuum advance solenoid, which then goes on to supply vacuum to the distributor (advance). (Right?)

So, I’ll look more into that to figure this out. Is there a “trick” to mounting throttle cable to the clip to the valve cover, from the de-ice recall kit? I kind of suspect that’s where the binding might be?


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[Bitsyncmaster]

When I first bought my car, I found the throttle cable clamp on the passenger side valve cover had worn through the plastic coating and the that caused the cable inside to rust there and stick.

[Ron]

Either that or we are getting enough cars for a great discussion/techsession.

So - yeah… I looked into the throttle cable/body area and can tell that something is binding somewhere, b/c the throttle doesn’t automatically reset to nil after I release the throttle pedal and/or cable (if pulling from the engine bay).

When I manually push it to nil, rpms drops to 700-750 ish and stays steady (if a little rough).

This also seems to suggest that the idle creep up I was experiencing earlier is because the throttle spool doesn’t rotate far enough back to activate the idle speed microswitch, which causes opening the vacuum advance solenoid, which then goes on to supply vacuum to the distributor (advance). (Right?)

So, I’ll look more into that to figure this out. Is there a “trick” to mounting throttle cable to the clip to the valve cover, from the de-ice recall kit? I kind of suspect that’s where the binding might be?


Sent from my iPhone using Tapatalk Pro

Mine was binding like Dave's when I got the car.
But years later, it was the rod joints got too sloppy. Seems I had to adjust it a tiny bit longer so it would push the butterfly/lever shut, instead of shorter as Andy mentioned???

[82DMC12]

Mine was binding like Dave's when I got the car.
But years later, it was the rod joints got too sloppy. Seems I had to adjust it a tiny bit longer so it would push the butterfly/lever shut, instead of shorter as Andy mentioned???

I haven't been in this thread for a while because I've been distracted by a couple other issues. However to address Ron's last question, the rod actually has to be made shorter if you want to take up slack AND pull the throttle arm so that it presses more firmly against the stop plate.

Here's a little update from my car. I'm not sure where things started to go a bit wrong again, but they are. I can start the car cold and it will start at about 775 RPM, but then within a few minutes as things warm up, the idle slowly comes up to around 1,000 - 1,100. This is just letting the car idle without ever touching the throttle. If I goose it while in neutral (manual trans) sometimes the RPM's drop back down to 775 however when it is at 1,000 it is NOT because the throttle is binding, that I am 100% sure of. The throttle is as closed as it can be and the stop screw is as backed out as it can but still take the abuse from the throttle spool snapping back on deceleration.

I DID BUY A SMOKE MACHINE and I have confirmed there are NO vacuum leaks on a cold engine. Last night I ran the car until the fans came on, then shut it down and did another smoke test on the HOT engine - no smoke leaks except a tiny bit from the oil dip stick which probably isn't actually a vacuum leak since the engine would be sucking the stick downward in normal operation. So I think I have completely ruled out vacuum leaks.

I'm really at a loss as to what else to check. I've gone over everything multiple times.

I did pull my spark plugs out this weekend to check them and all of them look like they've been running somewhat hot. Here a couple pictures of them so I'd be glad to get all your opinions. They are NGK 2238 TR5's and only have maybe 250 miles on them. I recently learned that an NGK heat range of 5 is more like an 8 in Bosch-speak so I think they do run hot. I'm replacing them Bosch HR6DC's that I found on ebay (copper instead of OEM silver). I do think my idle is a bit rough so maybe these NGK plugs are not good.

I pulled the distributor out to check the reluctor air gap since I did replace the impulse coil a few months ago but didn't know the gap was a "thing". It's now gapped exactly perfect.

CO has been checked multiple times and everything is in spec.

Timing has been checked multiple times - perfect. Also put a light on each of the six plug wires and they are all flashing consistently so I'm not losing a cylinder here and there.

I checked injectors again by placing them in glass jars and jumping the RPM relay. No drips with a neutral air plate and no drips after pushing down on the plate and releasing it. The spray pattern looks good on all six and the volume is equal after 30 seconds. I'm going to check fuel pressures one more time just to make sure my control pressure isn't F'ing up.

Not too such what else to do unless my idle motor is somehow defective, or my non-collapsed decel springs are too lose to keep the throttle buttons closed when they warm up. I might have to buy a new throttle body and just try that.

PXL_20220530_165648667.jpg PXL_20220530_165700968.jpg

[Bitsyncmaster]

Here's a little update from my car. I'm not sure where things started to go a bit wrong again, but they are. I can start the car cold and it will start at about 775 RPM, but then within a few minutes as things warm up, the idle slowly comes up to around 1,000 - 1,100. This is just letting the car idle without ever touching the throttle. If I goose it while in neutral (manual trans) sometimes the RPM's drop back down to 775 however when it is at 1,000 it is NOT because the throttle is binding, that I am 100% sure of. The throttle is as closed as it can be and the stop screw is as backed out as it can but still take the abuse from the throttle spool snapping back on deceleration.

That's what my car did for so many years and it turned out to be bad deceleration springs. So far if you look at the springs and see uneven coils you know it's bad but I wonder if good looking springs can go bad.

My car would idle at a perfect 775 RPM cold and would end up at 1000 RPM warm and I had the curb idle screw fully backed out.

[82DMC12]

That's what my car did for so many years and it turned out to be bad deceleration springs. So far if you look at the springs and see uneven coils you know it's bad but I wonder if good looking springs can go bad.

My car would idle at a perfect 775 RPM cold and would end up at 1000 RPM warm and I had the curb idle screw fully backed out.

I've been avoiding blaming the decel springs because there is no easy fix besides replacing the throttle, and those are hard to find now. I see DPI has a "refurbished" throttle available for about $400 and Ed seems to have a NOS throttle for about $500 USD. Doesn't show available via DMCH website but sometimes there's a solution. I have also avoided blaming the springs because they are not collapsed.

If anyone out there has a known good throttle body I'd be glad to pay shipping both ways if you'd be so kind to loan it out for a test!?!

[Bitsyncmaster]

I've been avoiding blaming the decel springs because there is no easy fix besides replacing the throttle, and those are hard to find now. I see DPI has a "refurbished" throttle available for about $400 and Ed seems to have a NOS throttle for about $500 USD. Doesn't show available via DMCH website but sometimes there's a solution. I have also avoided blaming the springs because they are not collapsed.

If anyone out there has a known good throttle body I'd be glad to pay shipping both ways if you'd be so kind to loan it out for a test!?!

With engine swaps and a lot of EFI the throttle bodies should become more available and priced less. In the past you could find them for less $100. If you can find a way to lock yours down to test, that would also work. Maybe some hot glue.