Sometimes when it rains (or i give it a good wash) epc would go on in my car followed by a check engine light and limp mode. once it dries up, the car is running good, the epc and check engine lights go off (the first time it happened, i got a P2138 code) im driving a 2001 a4. could it be bad wiring? where should i look ?

 

I'm guessing you've got a plugged drain hole, somewhere; but I'm betting YOUR farm on the guys in this sub-forum being able to better dorect your efforts than I.

Guys!!!

 

Does your car have an automatic transmission? If so, it's possible the front-passenger side sunroof drain is clogged and it's draining to under the carpet where the TCU is (passenger-front floor area).

 

The car is stick shift. I'll try to look this weekend

 

update:
heavy rain yesterday, on my way from work epc light came on, car was in limp mode. what someone told me to check was if my driver side carpet was wet- it is wet. the code i got today was p2128. help pleasE!

 

If you clear the code, does it come back?
My guess would be the water/moisture is causing an issue with the wiring harness, like a temporary short. You need to find out why the carpet is getting wet - it's likely due to a clogged drain line, either for the sunroof or battery.