Weird O2 readings..

[fishstick41]

Hey,
I am having problems with the upstream o2 Sensor. What is happening is if I am idling it jumps from ~4.00 (mA) to ~200.00 (mA). This is tripping my check engine light giving me a po420 code. I have had this problem many times before and this is the second time I have changed the sensor. I am wondering if anyone has any clues?

Thanks,
Martin H. Lawton

[fishstick41]

oh, here are the things that I have done,

1. change OE coil packs to the 2.0 coil packs
2. new fuel injectors
3. currently changing the fuel injector wires(finished 2 and 3 waiting for more to come in)
4. new valve cover and intake gaskets
5. new check valves(hasn't done them all just the ones under the intake and the one on the airbox)
6. new breather hose.
7. replaced old and cracking hoses.