Hi all thought I would post this regarding P0172 and P0175 codes triggering restricted performance
I have a 2000 XKR and started getting the restricted performance would clear the code and after second start it would come back.
I took the time to go through the system as i noticed others had struggled with this.
steps I took
Checked fuel pressure all good 40psi
Checked evap system purge valve working good

I purposely left the MAF sensor untill the end
Hooked up my code reader put it into live data and got readings for short and long term trim very high - 20% and over on bank 1 and 2 short term trim -7% on bank 1 and 2. Basicly telling me the ecu was trying to lean out the mixture but couldn't.
couldn't 1st step I cleaned the MAF with the MAF sensor cleaner made a small difference but still triggered the restricted performance.
next unplugged the MAF sensor connectconnector it was not making great contact cleaned the connector and gave the connector plug a bit of adjustments to make sure they were a nice tight connection.
plugged in my IDS system checked voltages to MAF sensor all good.
Cleared the codes with my IDS system took the car out for a good drive highway and city. Wow what a difference long term trim down to -7% on bank 1 and 2 short term down around -3%
as I drove the trims were very responsive to throttle and cruising the car was much more responsive
on another note I had the litres untill empty on the dash and drove about 100 kilometers my fuel economy dramatically improved the read out at the beginning of the drive said 140 km to empty, and average fuel economy was 14 litres per 100km(15mpg sorry in in canada lol) I drove 100km (60 miles) and the readout now said 110km to empty and average fuel economy dropped to 10 litres per 100km(24.5 mpg)

So the solution was a poor connection of the MAF sensor hope this helps
on a note these codes started showing up after i had it in for an oil change i think because the MaF sensor is mounted on the air tube when the tech checked the air filter lifting the air box cover that little bit of movement may have been the last straw for the connection because it was after the oil change the restricted performance started showing up

Cheers

 

If you had grown up with a Bosch L-Jetronic fueled car, you probably would have gone straight to the MAF connector. Because this was years before OBD1 or 2. Dealers of BMW, Fiat and others would sell unwary customers a new MAF unit when their cars came in for service. All that it usually took was to pull the connector from the MAF, a swab of dielectric grease on the multipin connector, plug it back in, and go. Those low current contacts are sensitive to the under-hood temps.