Hello, my 1996 subaru legacy used to have a cel code p0121 that would appear and disapear at random. Now it stays on all the time and I randomly will have a major low end power loss and heavy fuel consumption. I tested the tps and it seems to work just fine. disconnecting the batt for a a lil while will remove the problem for a while then it will come right back. odly enough though the idle used to be all messed up but the car ran well, now it idles very nice but the car has no power. not sure if its worth noting that the problem appeared after adjusting the clutch.

You said you adjusted the clutch, so I assume you have a cable operated clutch, do you also have the hill holder?    If so your brakes may be dragging.

How did you test it?

The computer has to see the correct voltage signal from the TPS or it will cause power problems and set codes.

This isn't a very common failure, it probably just needs to be properly adjusted.

ECU needs to see 0.5V from the TPS at closed throttle.

I tested it with a multimeter, and get the correct voltages. though that code isnt the one showing, it used to show back when it idled too high. I assumed it was the same code, as the cel never went off from then till this problem occured. I just got the new code at its saying knock sensor, So I checked the knock sensor and it has a crack in it though the surface it was on was immaculate. Ill change that out and report back.

Knock Sensor will cause your symptoms, power loss and high fuel consumption as it retards the idle.

Make sure you clock the new on correctly.

Larry

If you get misfire only when warm, then you might want to suspect your front 02 sensor.

So I changed out the knock sensor and so far thats been the fix. got it for 79 after tax, my old one had a big crack in it. thanks for all the input.