Thermo Time Switch -idles bad when plugged into vac source, good when not.

[DeLorean]

My Thermo time switch.

Seems to be hooked up correctly, however I recently fixed a few vacuum leaks other places and now the car idles a little worse and I noted the following.

When the thermo time switch is plugged into it's vacuum source (I.E., the intake manifold) the car idles higher than normal, runs rich and tends to misfire a bit at idle. With the vacuum source un plugged from the intake manifold (line plugged on both ends) the car idles down to a normal range, stops misfiring, and seems to generally idle better.

What's my issue here? DO I have a defective thermo time switch?
http://store.delorean.com/images/Product/medium/102405.JPG

Only a $40 bit, probably an hour or 2 to change?

[DMCMW Dave]

That is actually the thermal vacuum switch. If it has fails internally it can cause what you see. It should send vacuum to the warmup regualator ONLY when the engine is cold, and to the ignition distributor via the electrical vacuum switch ONLY when warm. If you have vacuum from it all the time it has failed. Under certain circumstances this can cause the warmup regulator to "go rich" when it shouldn't be. You should also verify that the hoses from that switch to the warmup regulator are connected per the diagram on the engine cover, and that the delay valve is not backwards.

A bit more complex to change than you think as the intake manifold has to come off, and you will lose a bit of coolant into the valley when you remove it.



My Thermo time switch.

Seems to be hooked up correctly, however I recently fixed a few vacuum leaks other places and now the car idles a little worse and I noted the following.

When the thermo time switch is plugged into it's vacuum source (I.E., the intake manifold) the car idles higher than normal, runs rich and tends to misfire a bit at idle. With the vacuum source un plugged from the intake manifold (line plugged on both ends) the car idles down to a normal range, stops misfiring, and seems to generally idle better.

What's my issue here? DO I have a defective thermo time switch?
http://store.delorean.com/images/Product/medium/102405.JPG

Only a $40 bit, probably an hour or 2 to change?

[DeLorean]

Aah, makes sense. Seems like the WUR NEVER gets vacuum signal. I would guess that this switch must be defective.

Guess it's time to pop on into the "VOD" Never been done in this car. What else should I replace while I'm in there?

[Bitsyncmaster]

Make sure your idle switch is working before you go to hassle going into the valley. You can test if your problem is ignition advance by just pulling the hose off the distributor. If your idle improves, your getting advance when you shouldn't.

[DMCMW Dave]

Agreed - before you take it all apart use a vacuum gauge (or your finger) to verify where / when you do and don't have vacuum at the various temperatures and throttle positions.

Here's a quick logic table:
Cold engine /throttle at idle - vacuum at warmup regulator tee, no vacuum at distributor vacuum switch
Warm engine /throttle at idle - no vacuum at warmup regulator tee, vacuum at distributor vacuum switch, NO vacuum at ignition distributor
Warm engine / throttle off-idle - no vacuum at warmup regulator tee, vacuum at distributor vacuum switch, vacuum at ignition distributor

[DeLorean]

The fault I seem to have here is at Idle, when warm, I have vacuum at the distributor. un plugging the vac advance vacuum line makes it idle correctly. - I guess this means the switch IS faulty? There is also a check valve at the T, could this affect operation? Any chance I could try blowing out the switch with some compressed air to free it, or is it probably just shot?

[Bitsyncmaster]

The fault I seem to have here is at Idle, when warm, I have vacuum at the distributor. un plugging the vac advance vacuum line makes it idle correctly. - I guess this means the switch IS faulty? There is also a check valve at the T, could this affect operation? Any chance I could try blowing out the switch with some compressed air to free it, or is it probably just shot?

It could be your switch or the vacuum solinoid. Make sure that solinoid is plugged in. The connector falls of very easily. You can test the switch with an ohmmeter.

[DMCMW Dave]

The fault I seem to have here is at Idle, when warm, I have vacuum at the distributor. un plugging the vac advance vacuum line makes it idle correctly. - I guess this means the switch IS faulty? There is also a check valve at the T, could this affect operation? Any chance I could try blowing out the switch with some compressed air to free it, or is it probably just shot?

Is the idle stop screw actually pressing the microswitch at idle? Check the electrical connections. If power is OFF to the vacuum valve, the valve is open. So the valve is not necessarily bad. Could be a bad idle microswitch as well, and actually more likely. Also not uncommon for the wire to fall off the valve.

The check valve at the tee is only "in play" when cold, and they rarely fail. Installing it backwards can do some strange things but that's not your problem.

[DeLorean]

Is the idle stop screw actually pressing the microswitch at idle? Check the electrical connections. If power is OFF to the vacuum valve, the valve is open. So the valve is not necessarily bad. Could be a bad idle microswitch as well, and actually more likely. Also not uncommon for the wire to fall off the valve.

The check valve at the tee is only "in play" when cold, and they rarely fail. Installing it backwards can do some strange things but that's not your problem.

Fixed!

Idle stop screw is set right & was actuating the throttle microswitch, and at first, it appeared that the vacuum solenoid was plugged in properly. I went to un plug it for further testing and I noticed that the one terminal was bent over and was not plugged into the connector! Flattened it out, plugged it in PROPERLY, and shes all set. Now has a nice smooth idle and cuts off the vac signal to the distributor when it should. Wonder if it came like this from the factory??

Thanks for the help!