I ran through the diagnostic procedure, per your instructions. It says to apply vacuum to the lower hose from the engine mount solenoid valve (hose runs to the mount) for 20 seconds, then release and reapply vacuum and check for any notable change in idle quality. There was no notable change.

 

Does the mount hold vacuum?

 

Yes, but there is no change in idle either with or without vacuum. Could I have mixed up the instructions?

 

I was thinking that you may have a vacuum leak somewhere in the mount or vacuum hose that could cause a strange idle problem. I'm not sure if I'd replace the motor mount if the components hold a vacuum.

 

Could the solenoid valve possibly be bad, if not a vacuum hose? There was voltage going to it.

 

How did you judge the idle to be the same?

Applying vacuum or not to the rear engine mount doesn't really change the idle. What you're looking for is whether a lot more vibration is transmitted so you can feel it when sitting inside the car. Also the test is with the transmission in gear & holding the brake.

1) Engine & transmission all warmed up.

2) Park the car, engine running, with 2 people. One at the drivers seat, one at the open hood with vacuum pump or unplugging the electrical connection or ???

3) Engine idling, shift the transmission into DRIVE, and hold the brakes.

4) Other person disconnect the vacuum hose or wiring (as per the testing instructions).

5) The person in the drivers seat is looking for the level of vibration to get worse when that vacuum-operated mount is switched on & off.

 

That vacuum operated mount is only for automatic transmission. The only time it is activated is as follows:

- Transmission in gear (DRIVE or REVERSE).
- Engine idling (according to throttle-position-sensor).

I don't have that car anymore, so I don't remember whether applying vacuum switches the mount into the soft mode or the stiff mode.

 

Okay, I didn't realize that the transmission was to remain in gear throughout the test procedure. I judged the idle based on the car being in park. I'll run the test again this evening and let you know what comes of it.

The car does vibrate considerably when stopped in drive, like at a traffic light. Which seems to me to support the possibility of a bad mount or related component of that system.

 

In gear, stopped at a traffic light, is the exact situation where the mount has to switch into the "soft" mode.

If it doesn't switch into the soft mode, you are looking for "why not".
- proper circuit connected to the vacuum solenoid valve?
- proper vacuum hoses connected & not leaking?
- mount itself broken & not holding vacuum?

 

Well, ran the test again and came to the same result. The procedure does state to shift it back into either N or P, which I did. The solenoid valve has power going to it under the right circumstances, and the hoses are not leaking. The mount holds vacuum and there is manifold vacuum from the other hose. Can the mount hold vacuum and still be faulty?