VVIC, On the fuel filter, I'm going to say no... A clogged fuel filter isn't going to be OK one minute and then blocked the next minute. Your particular issue sounds more like an intermittent electrical connection with one of the major inputs for the ECU. These are:
- AMM (MAF sensor)
- coolant temp sensor w/ bad connection or high resistance reading (all other wiring for the CTS back to the ECU being OK)
- Throttle position sensor

Probably not going to be an O2 sensor. Try disconnecting one at a time. The ECU should revert into a "limp home" mode and use data from the remaining sensors. By not receiving conflicting data, it will usually run better albeit "protectively" rich.

Also, be sure to check all grounding connections. I have a few nice jumper wires (a wire with alligator clips on both ends) that I keep on hand to make additional grounds. Jump from the cylinder head to the chassis and from the block to the chassis to eliminate the possibilty of a bad ground connection.

Steve