I writing this for a friend that has a 2000XKR. Has about 85K on it and has been having a huge problem with the P0171 and P0174 codes and RP. He has a new inlet pipe from air filter to throttle body so definitely no cracks or leaks.

We reset the codes and went for a drive and it set another prelim. code of p0171 and 0174 again.

I can do frame monitoring on the scanner and at the same approx speeds 71-73 range mph you would notice one frame where the short term fuel trims were at 25 on both sides and the very next frame they would be at -14 to -18 on both sides and then back up to the 25 on the next frame. They may also float from a plus 18-19 to a minus 7 or -8 at the same even speed with no load increase or noticeable decrease. The idle is "slightly" rough.

Now this is not good. I have previously run the idle and 2500 rpm test and you go from the zero to 19 or so on fuel trims.

However the situation where at the same speeds the fuel trims in less than 10 seconds would go from a plus 25 to a -14 or -18 is a drastic change and does not sound like solely a vacuum leak or a vacuum leak at all.

I am making a bet on the MAFS being bad. I have personally thoroughly cleaned it as I have had that problem on my S-type and understand what is involved.

Any suggestions with the fuel trims running all over the place. That sounds much more electronic or sensor related that a mechanical issue like a straight up vacuum leak. He also had someone else run a smoke test and had some around the seal to the throttle body and that was fixed, but still the wild variation in the fuel trims and with the p0171/0174 codes. About 3 years ago he had a head gasket job done (done by Jag Mac and Russell knows what he is doing).

Help is greatly appreciated as he needs to pass an inspection.

thanks

Tom in Dallas/Plano ( in the role of a proxy)

 

yeah read my post I just started .

A.
Remove the air intake, remove the Throttle Body, 4-10mm bolts, 2- 8mm bolts

3 electrical connections, 2 hoses.


The bolts for the EGR have come loose allowing the lower throttle body to suck in raw air after the MAF. AKA VACUUM LEAK

they are two 8mm, simply tighten them or replace them if they are missing.Don't over tighten.
B.
The black plastic tube that runs from the passenger lower throttle body inlet has a grommet that's worn allowing air in,pull out a lil, wipe with a clean towel, apply rtv around it, push back in, let dry overnight.

C.
There is a ambient air temperature sensor that will have oiliy residue, its on the passenger side rear upper manifold, like 22mm socket to remove I think.
Wipe the tip with a clean towel. Lightly rtv its copper washer and screw back in tight so its not leaking.

Those will cure your problems and take 25 mins to complete. You will have to reset your codes with the scanner or remove the negative, an hold it it on the positive for 30 secs. If you do that, you will have to do the window re-learn, have your radio code If applicable, and reset your clock..

 

Would that explain the fuel trims at a constant speed going from +25 to a negative 18. Would not a leak of this nature cause a reading that stayed one direction or another and not vary by almost 40 steps to the opposite direction with the engine doing the same thing.

Just a question!

Tom in Dallas

 

Yea and it feels like a misfire.

The engine is vibrating on and off the throttle body, as the ecm is trying everything it can to correct the problem, and you may even have slow/old O2 sensors, making your condition even worse

 

There may be a small black hose that connects to the center section of the supercharger, just aft of the coolant plug (on the right side). It may have come loose and it's easy to miss. 0171 / 0174 & RP are immediate if it does come loose. It happened to me.