I have noticed the car vibrates at idle. When the car is cold and the rpm's are over 1k I don't feel it as much. But when she warms up real good and the rpm's are below 1k. It is noticeable. I was wondering if I needed to change the engine mounts? Is there any way to check them beside removing one and taking a look at the rubber? the car has 105k i don't think they have ever been changed.

 

My 2000 c4 has the same symptom except that it also has the following. At idle, after I blip the throttle, the rpm drops low and the engine feels like it is going to cut out but kept running and vibrates like the mount is bad. When I give it a little gas to try to keep the rpm steady at 1500 rpm, the rpm varies between 1200 and 1500 rpm like a sine wave on a oscilloscope and there's a steady vibration that feels like one of the cylinder is not firing. I got no check engine lights. I am wondering if my AOS is bad. Car has little torque at startup and power is not good and engines sounds stressed at rpm above 5k. Car has about 40k miles and I plan to do the clutch, ims in the near future. Would this be a symptom of AOS? I seem to be loosing coolant but checked both coolant tank and engine oil dip stick and didn't find any hint of intermix. Any suggestions for further check?

 

Could be also transmission mount or engine mounts. The later is easy to check, post a pic of the rear of your car.... If the space of the muffler tips is around quarter of an inch they should be ok. If the space is closer to an inch, they probably need replacement. As the engine is out of alignment it could lead to vibrations. There is a dyi at pelican forums. Piece of cake.

Transmission mounts on 99 cars is a *****, gotta remove the tranny for replacing a $100 piece. I believe in '02 cars is easier.

Or it could be something else as mentioned.

 

The symptoms read like a failed VarioCam solenoid. While there is no check engine light you should check for pending codes.

A VarioCam error code could be pending as the DME attempts to address the unacceptable fueling/combustion by adjusting the mixture. The VarioCam error code won't be set until the DME has reached its adaptation limits. Then you might get some mixture related codes, even misfire codes too, along with the VarioCam related error code or codes.

If I'm right you can see the difference in sensor readings from the bad bank and the good bank if you want to view these in real time as the engine runs and acts up.

However, I'm uncomfortable with running the engine any more than absolutely necessary when it is obviously sick. I would reserve any engine running for when a tech is at the car and is making a diagnosis.

Oh, for the coolant loss the most common reason for inexplicable and gradual coolant loss is the coolant cap. If an -00 or -01 replace with an -02 or -04 (is I believe the latest/greatest).

Also, check the water pump for any signs of coolant wetness or staining.

With the engine off of course give the serpentine belt a feel for sharp edges. Sharp edges arise from the belt rubbing an accessory drive pulley and this is due to mis-tracking due to excessive play at the accessory drive shaft bearings.

But take care of the source of the engine's misbehavior first.

 

Reads more like an AOS than a motor mount issue.

The mounts can be inspected with the car in the air by a tech under the car with a good flashlight.

One pointed out to me a failed motor mount in my 02 Boxster without even having to remove any underbody/engine panels. There were no signs the motor mount was bad but it was obviously bad, clearly the rubber was cracked/split and coming apart.

You should avoid running the engine any at all until the AOS has been eliminated. The AOS can go from bad to worse and put oil in the engine chambers and there's a risk of hydraulically locking the engine often with serious damage the result if this happens.

 

Check engine mounts anyway. Just look at tips as Indicated. Hopefully is not aos. At 100k chances are that mounts need replacement anyway.

 

Thanks for all suggestions. Would acquiring a durametric help in diagnosing whether a variocam solenoid or AOS failure? What would you test for besides reading fault codes if any? Thanks.

 

Those issues will be diagnosed I bet. If you'd like to take a look at a couple of DIY articles on AOS and motor mounts we've put together they are as follows:
Air Oil Separator
Replacing Your Engine Mounts

Mark/Pelican Parts

 

semi-ontopic: whos pass seat vibrates at idle?

 

The engine got rebuilt 3k miles ago. If they changed the aos I'm not really sure. I doubt the part could go bad in 3k miles. They inspected the car and drove it with me also, and it ran and sounded fine.

I took a pic of my tail pipe to see the space between it and the bumper and this is what I got.

 

OK. So I went to my indi shop and read the cell light. It was showing all 4 os sensors were bad. Went ahead and changed them. Now do I have to reset the cell for the light to go off or will it do it on its own?

 

The CEL should go away on its own but it can take some time. The DME must see the error condition absent a number of warm up cycles before it will erase the codes and thus extinguish the CEL.

But it is better if you clear the codes. So run out and get yourself an OBD2 code reader/data viewer. How much you spend is up to you.

Using one of these of course clears the codes and turns off the CEL, but also resets other stuff to their defaults. The benefit is the DME starts out with no goofy learned fueling/etc that might have come about from the bad sensors.

Also, with the CEL dark if another error code (or the same ones..) appear with of course the CEL coming on again you'll know it and can take immediate action.

Which is read the codes.