Another thing to look at is the throttle body and specifically the Idle Control Valve located on the throttle body. Many times particulary with the number of miles you have on your VX, the Idle Control Valve gets very dirty and sticks or stops working all together.

I had been dealing with P0101 codes setting and then turning off and rough idle especially after freeway driving for some time now. My VX had been to 3 different mechanics trying to diagnose the problem. None of them could find the problem. We determined that there was nothing wrong with the MAF as it is new and there were no vacuum leaks since we smoked the entire engine. The O2 sensors are all new and all other sensors and operating parameters checked out on the diagnostic equipment.

Finally last weekend I decided to take a look at the throttle body. It was in need of cleaning, but the ICV was really nasty. I cleaned the throttle body and ICV with throttle body cleaner. Now my VX runs better then it has in quite a long time with no idle problems and no codes. I also decided to buy a new ICV and I will install it this weekend. It's not that expensive about $45. I'd rather have a new one that I know is in perfect working order.