I have my car for about two years... during the two years, the rear drive side tire would leak about a pound of air a week. Every three weeks it requires 4 pounds of air. I've tracked the car a few times over the last two years and it showed no sign of any issue on the tire (except for the slow leak).

Here are some of the few things I've trying to isolate the leak.
1) Soap and Water spray
2) Tighten the value stem
3) Replace the value stem when I had to change the TPM sensors

(Possibly the rim???)

Looking for suggestions. Thanks!!!

 

It could be a very small puncture or problem with the edge/beading of the tire where it meets the rim. May also be the rim if it was curbed or hit a pothole. I'd take the tire off and examine it from the inside. If the tire and rim looks ok then try putting another tire on from someone who is replacing their tires. How many miles on the tire?

 

Even if it is the rim, a soapy water test should reveal a leak. Did they immerse the tire in a water trough? I once had Michelin PS2 with a white oblong tag fixed to the inside of the tire. During manufacture, it had been placed too close to the bead and was just enough to prevent a complete seal. Wasn't found until tire guys put the wheel in a tank.

 

Do you have cast, rather than forged, wheels ? If cast, a common problem is corrosion at the rim, just where the bead seats. It takes only a very small amount of corrosion to cause a leak. The solution is simple, quick, and inexpensive. Any decent tire/wheel shop has seen the problem many times. Fix is dismount tire, lightly sand rim, wipe clean, seal with one of several liquid goos (technical term), let dry, re-mount and balance tire.
I don't know if this problem can occur on forged wheels-frankly don'see why not, but i have not seen that personally. Hope this helps, and good luck. BTW, everything else you've done seems logical. You do appear to have covered all the other bases.

 

My uncle used to own a shop. For difficult leaks to pin point, the dunk is the best way, second best soapy water.

 

Do you have a pool? Wash the rim and tire thoroughly then fill it w 45lbs of air pressure then put it in the pool....watch for air bubbles. There is a slight chane that it only leaks air while driving....if this is the case you will probably have to seperate the rim from the tire and inspect the tire besd and rim mating surfaces. I have never not been able to find (even the slowest) of leaks w the soapy water method.

 

+1 on submerging the complete wheel. I once had tires mounted and 1 still had a small sticker on the inside. That was all it took to leak very slowly....

 

Answering some questions that were asked:

1) Pot holes... sometimes can't avoid that. There's no scratch on the rim or tire. Don't believe I curbed the wheel since I purchased the vehicle, not sure about the previous owner.
2) Stock wheel with about 10K on the tire.
3) Tank test, have not done that yet... I need search a little harder for shop that can perform this type of test.

Thanks again everyone.