High idle, Idle speed regulator...?

[BigChapMatt]

Hi All,
The initial problem was my engine would stall/shut down when I take my foot off the gas and push the clutch in when cruising. This happened 60% of the time.
I assumed it was the idle speed regulator being a bit sticky.
So I removed the idle speed regulator, gave it a good spray out with brake cleaner, dropped a bit of 3 in 1 oil in it, installed the regulator and now she idles high at about 1200rpm.
I have checked lots of things. I don't think I disturbed anything in the process. Vacuum lines and linkages seem to be ok.
Tapping the gas doesn't bring the idle down.
If I unplug the regulator the idle comes back down. When I plug it back in, the idle goes up again.
Im not sure what the issue is.
Could the idle speed reg be faulty?
Thanks Guys.

[DMCMW Dave]

Deleted

[DMCMW Dave]

That may also be bad wiring to the regulator. If one of the three wires to it is not connecting it will do this.

[David T]

That may also be bad wiring to the regulator. If one of the three wires to it is not connecting it will do this.

Verify the throttle arm is tripping the idle micro to turn on the idle motor. Check for looseness (play) in the quadrant link ends between the throttle spool and the throttle arm.

[hmcelraft]

The adjustment on the micro switch (turning on the idle motor, etc.) is critical to giving the engine idle a "dash-pot affect" - and not letting the engine slow down too fast. I've been looking for the section in the manual that goes through that but I haven't found it yet. It in there because I have used it before - it has just been a long time. If that adjustment is out and allowing the idle motor to come on too quickly the engine will die just as you are experiencing.

[BigChapMatt]

That may also be bad wiring to the regulator. If one of the three wires to it is not connecting it will do this.

Hi Dave, the pins in the regulator plug look good. That doesn't mean the wiring is 100% Looking at the wiring diagram, the plug wiring goes back to the idle relay. I guess I can test the wiring between the plug and the relay. Is the relay in the fuse box area?

[BigChapMatt]

Verify the throttle arm is tripping the idle micro to turn on the idle motor. Check for looseness (play) in the quadrant link ends between the throttle spool and the throttle arm.

Hi David, the idle switch is being trigger when throttle is 0% and I've tested that the idle switch is functioning. All throttle leakages are not loose. When I unplug the idle speed reg, the rpm goes back to normal, from 1200 to 750. Plug it in again and the rpm goes high. I'm thinking its more an electrical issue rather than mechanical.

[BigChapMatt]

The adjustment on the micro switch (turning on the idle motor, etc.) is critical to giving the engine idle a "dash-pot affect" - and not letting the engine slow down too fast. I've been looking for the section in the manual that goes through that but I haven't found it yet. It in there because I have used it before - it has just been a long time. If that adjustment is out and allowing the idle motor to come on too quickly the engine will die just as you are experiencing.

It is possible that the micro switch could be coming on too early. I will double check that. That could solve the stalling issue.

The high rpm is the big issue at the moment. I will check the wiring is ok between the idle relay and the plug tonight.

If the idle speed regulator is holding the rpm high, does anyone know what conditions tell the regulator to hold the rpm high?

[Bitsyncmaster]

If your idle is to high, first thing to do is back the curb idle screw (lower screw) out a little and see if that drops the idle. You may have to adjust the idle switch when you adjust that lower screw also.

If you find you need to back that curb idle screw all the way out, you need to check you deceleration valve springs. Just looking at the springs usually tells you if they are the bad ones. The spring coils are not evenly spaced on the bad ones. With bad springs, you usually have good idle on the cold engine and about a 1000 RPM on the hot engine (with the curb idle screw all the way out.

[BigChapMatt]

If your idle is to high, first thing to do is back the curb idle screw (lower screw) out a little and see if that drops the idle. You may have to adjust the idle switch when you adjust that lower screw also.

If you find you need to back that curb idle screw all the way out, you need to check you deceleration valve springs. Just looking at the springs usually tells you if they are the bad ones. The spring coils are not evenly spaced on the bad ones. With bad springs, you usually have good idle on the cold engine and about a 1000 RPM on the hot engine (with the curb idle screw all the way out.

Im a bit reluctant to adjust the idle screws because yesterday, before I removed and installed the idle speed regulator, the idle rpm was perfect.
I therefore think the linkages and screws should be ok. Wouldn't adjusting something mechanically just compensate for what the real unknown issue is?
Is the idle speed regulator supposed to be fully closed when the engine is idling at normal 750 rpm?

[Bitsyncmaster]

Im a bit reluctant to adjust the idle screws because yesterday, before I removed and installed the idle speed regulator, the idle rpm was perfect.
I therefore think the linkages and screws should be ok. Wouldn't adjusting something mechanically just compensate for what the real unknown issue is?
Is the idle speed regulator supposed to be fully closed when the engine is idling at normal 750 rpm?

Most idle motors do run almost fully closed when the engine is warmed up. It all depends where that curb idle is set. Any vacuum leaks will also make it run more closed. Also make sure your ignition advance connector on the solenoid has not fallen off (very common problem). That would mess up the idle.

[BigChapMatt]

Most idle motors do run almost fully closed when the engine is warmed up. It all depends where that curb idle is set. Any vacuum leaks will also make it run more closed. Also make sure your ignition advance connector on the solenoid has not fallen off (very common problem). That would mess up the idle.

Thanks for replying again Dave.
What make the idle higher? When it's more closed or more open...?
Ok, the ignition advance connector, where is that..? I'm not sure what that is. Is it a vacuum connector or electrical plug...?

[Bitsyncmaster]

Thanks for replying again Dave.
What make the idle higher? When it's more closed or more open...?
Ok, the ignition advance connector, where is that..? I'm not sure what that is. Is it a vacuum connector or electrical plug...?

When the idle motor opens, it increases the RPM. The two pin electrical connector, plugs into the vacuum advance solenoid at the back of the engine (behind the fuel distributor).

[BigChapMatt]

When the idle motor opens, it increases the RPM. The two pin electrical connector, plugs into the vacuum advance solenoid at the back of the engine (behind the fuel distributor).

Ah yes, will have a look at the plug...
Ok, assuming the engine is up to temp and the rpm should be low/normal at about 750, the idle speed reg should be closed. Do you know what tests I can do on the regulator plug with a multimeter to see if the reg is actually being told to close...?

Thanks.

[Jonathan]

Ah yes, will have a look at the plug...
Ok, assuming the engine is up to temp and the rpm should be low/normal at about 750, the idle speed reg should be closed. Do you know what tests I can do on the regulator plug with a multimeter to see if the reg is actually being told to close...?

Thanks.

Have a look at this pic Matt:

http://dmctalk.org/showthread.php?10336-Assorted-helpful-technical-photos&p=165043&viewfull=1#post165043

In the photo, the electrical connector is not on, so you can see the two metal tabs. You can also see where the two vacuum hoses go. One is on and one is not.

If I'm not mistaken, to test whether your solenoid is working correctly, you should be able to take off the one hose and feel with your finger whether it is trying to pull vacuum against the skin on your finger tip. I don't remember which hose to try this on, sorry, someone else can chime in. If the solenoid is working and gets a signal from the electrical connector, it will go from no-suck to suck on that vacuum hose barb. If it isn't working, you won't feel a change when the electrical signal is changed from on to off or back to on again.

[Bitsyncmaster]

Ah yes, will have a look at the plug...
Ok, assuming the engine is up to temp and the rpm should be low/normal at about 750, the idle speed reg should be closed. Do you know what tests I can do on the regulator plug with a multimeter to see if the reg is actually being told to close...?

Thanks.

It's a pulse width signal on the two outer pins. Not sure if your meter can read duty cycle. One pin runs at the opposite of the other pin. So if one had a 10 % duty, the other would have 90 %.

What you can do is after the engine has warmed up, shut off the car and remove the idle motor and look if it is almost closed.

Here is a video of a Volvo idle motor working. The DeLorean idle motor works the same but is not as smooth as the Volvo unit.

https://www.youtube.com/watch?v=8YE_HG4ji8E

[BigChapMatt]

Have a look at this pic Matt:

http://dmctalk.org/showthread.php?10336-Assorted-helpful-technical-photos&p=165043&viewfull=1#post165043

In the photo, the electrical connector is not on, so you can see the two metal tabs. You can also see where the two vacuum hoses go. One is on and one is not.

If I'm not mistaken, to test whether your solenoid is working correctly, you should be able to take off the one hose and feel with your finger whether it is trying to pull vacuum against the skin on your finger tip. I don't remember which hose to try this on, sorry, someone else can chime in. If the solenoid is working and gets a signal from the electrical connector, it will go from no-suck to suck on that vacuum hose barb. If it isn't working, you won't feel a change when the electrical signal is changed from on to off or back to on again.

Good info. Thanks Jonathan.

[BigChapMatt]

It's a pulse width signal on the two outer pins. Not sure if your meter can read duty cycle. One pin runs at the opposite of the other pin. So if one had a 10 % duty, the other would have 90 %.

What you can do is after the engine has warmed up, shut off the car and remove the idle motor and look if it is almost closed.

Here is a video of a Volvo idle motor working. The DeLorean idle motor works the same but is not as smooth as the Volvo unit.

https://www.youtube.com/watch?v=8YE_HG4ji8E

Looks like the vacuum advance solenoid may have been the culprit. I pulled the plug, sprayed with contact cleaner and reseated the plug. Started the car and rpm was back to normal straight away....:):):)
Dirty pins after 30 plus years I guess. I haven't run it to full warm temp yet but looks good so far...

Thanks a million Dave and all others involved...

[Bitsyncmaster]

Looks like the vacuum advance solenoid may have been the culprit. I pulled the plug, sprayed with contact cleaner and reseated the plug. Started the car and rpm was back to normal straight away....:):):)
Dirty pins after 30 plus years I guess. I haven't run it to full warm temp yet but looks good so far...

Thanks a million Dave and all others involved...

I bet that connector is 25% or more of sudden idle problems. I added a new two pin connector and soldered the wires onto the solenoid so it could not fall off again.

[Jonathan]

Looks like the vacuum advance solenoid may have been the culprit. I pulled the plug, sprayed with contact cleaner and reseated the plug. Started the car and rpm was back to normal straight away....:):):)
Dirty pins after 30 plus years I guess. I haven't run it to full warm temp yet but looks good so far...

Thanks a million Dave and all others involved...

Glad to hear!


I bet that connector is 25% or more of sudden idle problems. I added a new two pin connector and soldered the wires onto the solenoid so it could not fall off again.

Thanks for mentioning Dave. I'll add this connector to the troubleshooting tacklebox for sure. High idles on our cars seem to be about the most common problem experienced based on my own and what I have seen from others. Cheers.