98 qx4 losing power while driving.

[ipeelscats]

Lately my qx4 has been having some issues. Sometimes it will bog when accelerating, then most of the power comes back around 2500 rpm yet it will randomly buck a little while driving 45-60mph. The truck seems to idle ok. I have replaced the MAF and Distributor. I have also cleaned the throttle body and changed the air filter. I am getting no codes except knock sensor (always been there). I am at the end of my rope with this truck. This thing wont stay fixed for more than a week. The distributor has been changed 3 times, most recently with a new unit. The MAF has been changed twice. I am using a regular Purolator air filter. Throttle body looks clean. Spark plugs and wires are ~2 years old. Fuel filter and pcv about 1.5 years. Anyone ever dealt with a problem like this?

[atraudes]

There's a couple of things that come to mind. I'd say run down the list and see what happens.

Spark plug wires - 2 years old isn't super old, but they're the usual suspect in power loss/bucking problems. If you're reluctant to buy new ones, check their resistance and see if you find any discrepancies between them. I'm not sure what it's supposed to be. Also look for cracks and such. One trick I heard was to watch the engine idling in the dark. If the insulation is too broken down, you may be able to see electrical activity between them.
Ignition module - If this wasn't part of the distributor that was replaced, more food for thought. I'm not sure if there's a troubleshooting routine for them, but the FSM would have it if there is.
Throttle position sensor - The FSM has some troubleshooting techniques for this. Make sure the resistances are within spec and increase smoothly as the throttle is opened.
Fuel pressure - Hook up a fuel gauge to the fuel rail and make sure you're getting the right numbers.
Cam/Crankshaft sensor - This feels like a last resort, but it's worth putting out there.

Good luck and let us know how you fare!

[ipeelscats]

So far, it looks like it was an 02 sensor.

[atraudes]

Aha, nice! That would make sense too. How did you come to that?

[ipeelscats]

I took it to my local shop. They have a much more comprehensive scanner than i do. The readings from the bank 1 sensor where throwing off the fuel trim. They replaced the sensor and cleaned some electrical connections. All is well.