Rough Idle Bad Gas Mileage

[jbjcjd]

Discovery Series II 2000 with 130,000 miles. I can not figure out what is wrong. Over the past few weeks I have noticed a rough stumbling idle (400-500 rpm) at a stop when the car is in gear (load on the engine). If I shift into neutral the idle returns to normal (750-1000) and is smooth. Also, if I sit at the light for an extended period the problem goes away (almost like the IACV is finally kicking in). Further, since this problem started I have been getting very low gas mileage (9.5 mpg) or about 180 miles per tank (I have seen other posts regarding rough idle and low gas mileage but no solution was presented).
I have cleanded the IACV thoroughly, all hoses around the intake have been cleaned, I just bought a new MAF 6 months ago and have cleaned that well with non residue cleaner and I let it dry before I put it back in. My oxygen sensors are about 18 months old. I ran two cans of seafoam thorugh the gas. I have new plug wires and plugs as of about 18 months ago.
I took it to an auto parts store and had them read the codes. Here is what i got:
0154 - 02 Sensor Circuit No Activity Detected (Bank 2 Sensor 1)
0174 - System too lean (Bank 2)
0300 - Random/Multiple Cylinder Misfire Detected
0308 - Cylinder 8 Misfire Detected

Any help would be much appreciated. Is the 02 sensor affecting my gas mileage this much? should I replace all 4 02 sensors if that is the problem? Could this be the TPS?

 

[joey]

From what you have listed, it sounds like you either have a bad O2 sensor on Bank 2... or worse case, the cam is starting to wear out....

A good read on engine issues.

http://www.rpiv8.com/engine-4.htm