I have a ford ranger 1998 3.0
I have got a code p0171
While I am moving, I have a high idle when I push the clutch in(1500rpms)
I'm sure the truck should not be idling that high with the clutch pushed in.
It kicks down to about 800rpms when i come to a complete stop.
I also have a lack of power.
I have changed the idle air controller, cleaned the maf sensor, changed the fuel filter twice, changed the pluggs.
any suggestions on what this might be?

 

P0171 is for fuel trim at adaptive limits bank-1, so something is going on with fuel trim on that cyl bank, question it what???? Do you have any other trouble codes, if so post All trouble code Numbers, as they can provide good trouble shooting clues.

If you don't have any more codes, the one thing that can affect fuel trim for an entire cyl bank, is an acting out O2 sensor, so if you have a scantool that'll monitor the O2 sensors output voltage & switching range, have a look at it & see if its switching speed & voltage range is up to snuff. It should be switching between 0-1 volt, fast.

If you don't have, or can't come by a scantool, try swapping the bank-1 & 2 upstream O2 sensors & see if the trouble code follows the sensor.
If it does & these are OEM sensors with 75-100K, or more miles on them, it's time for replacement.
Let us know what you find.

 

I don't have a scantool to try that, I did disconnect both O2 sensors and saw no improvement. I also removed them to see if I might have plugged catalytic converters. I was told it may be a vacuum leak at the intake manifold, but don't know how to test for that.

 

To test for intake leaks, you could rig an unlit propane torch with a length of tubing, & on the free end use a sports needle as a probe, to pass along the gasket area & listen for a change in engine idle rpm. The propane is sensor & cat safe. However an intake manafold vacuum leak would likely affect Both cyl banks & you've only posted a code for cyl bank-1.

Do the O2 sensor swap between banks & see if the trouble code follows the sensor & let us know how it goes.