So here's what I have a 2000 XJR throwing the occasional check engine and RP lights. P0172 and P0175 rich codes. I had this problem about 6 months ago and it finally gave me a Mas Air code as well, replaced and no issues or lights for 6 months straight. Then back again. Same codes. They come and go and even the check engine light sometimes goes away on it's own. Seems to throw the RP more at idle so I'm maybe thinking it is a TPS issue, perhaps it's seeing throttle when 0 throttle is given. Anyone have thoughts? What is the static fuel pressure suppose to be on the car? I want to start investigating this week. Any help would be appreciated as I know a lot of members here have a lot of experience with these cars. Thanks again.

Side note but highly unlikely, the car has a 4.5 lb pulley from the precious owner unsure if he ever got it turned or not, so maybe thinking the added boost is being seen by the ECU and maybe throwing the code but the 6 months of no issues is leading me to this not being possible.

 

check for air leaks after the MAF to the throttle body. No matter how well i thought i secured it, it would leak air in that terrible design. I ended up making my own 3.5in intake and all codes went away.

 

we had a coil breaking down,some days good others drove like a v6,changed coil all good

 

Check your intercooler aux. pump fuse and make sure the pump is operating while the ignition is on.

 

I pulled the codes again today while I had the RP active.

P0172
P0175 the two rich codes each bank
P0101 airflow values out of range (literally a brand new MAF sensor)

Marco, where was your leak? And do you have any picks of your fix. I will check the other suggestions as well thank you all for the replies.