Cabin Vibration

Hi...have not been here for many years. Hope you don't mind me asking a question about my 99 Avalon because not much action on the Avalon forum.

Have been chasing a cabin vibration for a couple years now. You feel it mostly in the steering wheel when the car is stopped in gear but not so much in neutral or park. Have replaced all mounts with OEM...no effect. The car idles beautifully and has plenty of pep. Fuel trims are perfect (short term at 0 +/- .8 and long term +/- 3) and have no CEL codes. However, if you put your hand on the intake manifold and rev the engine, when the rpms quickly drop, you can feel a pulsation almost like an out of balance shaft or restricted exhaust causing a pulsing back pressure. I do not know if this is related to or even causing the cabin vibration but I suspect it is.

Does anyone have any ideas or even a wild guess or to what is going? Thanks.

I would start by cleaning the throttle body if that has not been done recently.

Mike

Also, check your vacuum hoses and connections - replace any that are suspect.

I would start by cleaning the throttle body if that has not been done recently.

Mike

Thanks Mike. Glad to see you are still here. Cleaning TB was one of the first things I did. It wasn’t very dirty...did not make any difference. Car idles beautifully.

Also, check your vacuum hoses and connections - replace any that are suspect.

Can’t find anything that looks amiss. Plus, a broken or unconnected vacuum line would likely cause poor idle and loss of power which I do not have. This is a real head scratcher!

Check your intake manifold vacuum at idle. Do you use any oil?

Check your intake manifold vacuum at idle. Do you use any oil?

Thx Brian, I will do that. Where is the best tap for the vacuum check? Not a drop.

Thx Brian, I will do that. Where is the best tap for the vacuum check? Not a drop.

Any accessible port that is threaded into the intake plenum. You may need to plug the hose or fitting which is disconnected from the intake.

Any accessible port that is threaded into the intake plenum. You may need to plug the hose or fitting which is disconnected from the intake.

OTC gauge on order. Will report results.

Vacuum looks perfect. Rock steady 21” at idle and normal operating temperature. When I snap throttle, vac drops to zero, jumps to 23/24 and settles back to 21, just like it should. Vac holds steady at 2500 rpm so probably no restriction in exhaust. As suspected, my engine is purring right along.

I am beginning to think I may have an issue in the tranny, maybe lost weights from flex plate or torque converter problem. At this point I am going to drive her until failure.

Sorry I couldn't be more help. Good luck.

Thanks Brian. Even though I can not see anything wrong with the transmission mount, I am going to replace it because I have run out of things to try. I can not find a DIY tutorial or video showing how to replace the tranny mount on the 99 Avalon/Camry V6. It looks like it could be simple but maybe not. The lower captive studs that drop into the subframe are long. Not sure if I can lift engine high enough to clear. Has anyone done this job? Do I have to drop subframe?

Edit: I found a description but it does not ring true. I removed the nuts from the lower captive studs and lifted the trans. The subframe moved with the trans. In the description, the guy removed top four mount bolts first then lifted trans, removed lower nuts and removed mount. I don’t understand why his trans moved independent of the mount. I wonder if he had already disconnected front motor mount and maybe other connecting points before lifting trans? His write up was pretty detailed so I would not think he would have left out this important step.