Hello all,

Happy owner of a 2004 XJ VDP here, but with several codes occurring intermittently.

- P0121 - Throttle Position Sensor Range
- P0171 - Bank 1 Combustion too lean
- P0174 - Bank 2 Combustion too lean

Thank you for all the previous posts with great information regarding this issue.

0 ENGINE AND GEARBOX FAULTS
0 ENGINE SYSTEMS FAULT, DSC NOT AVAILABLE, PARK BRAKE FAULT. WHAT IS THIS?

To summarize those posts a bit, this code happens when:
- the Throttle Body gets dirty, or;
- when the TP sensor goes bad;
- cleaning the throttle body is bad;
- cleaning the throttle body is good.

The argument against cleaning the throttle body is that it removes a special coating (Some reference TSB XJ303-10, but I can't find a clean copy of that specific TSB online and it isn't posted on jagrepair.com). But others say that they have had great success cleaning the throttle body.

In fairness, the prices of parts for these parts has changed dramatically. For example, a replacement throttle body with the TP sensor included is only $282 (plus tax/shipping) from SNG Barratt. Some of the old threads speak to replacement costs upwards of $800 plus labor.

At that price, it seems to me that while I would be judicious in the use of throttle body cleaning chemicals, and be careful what bits I scrub, it seems sensible to give cleaning a try. My indie mechanic, who is a great guy, advocates just replacing parts until it is fixed and not cleaning. I think it makes more sense given the price of parts these days to check the connections as advocated above, clean the throttle body, and see what happens. As long as I don't break a connector, the worst case should be purchase of a new throttle body.

As to the lean codes, we think I have either a dirty MAF sensor, or some hose is rotted or a fitting is loose. I've got some time to address this on Sunday, so I was going to investigate that issue on Sunday while cleaning the throttle body.

So what say you gurus of the forums? Am I on track to success or failure?

 

I have cleaned a TB but only my spare (used) one.

I looks to me like the manufacturer or Denso or whoever may have

had problems with sticking butterflys in the very early days and they

have applied a black coating on the edges of the butterfly and on the

throat but only in the area of the butterfly when shut.

Cleaning should be a breeze if you use right solvet.

 

Well per the service repair manual:

145 .
CAUTION: Do not attempt to clean the throttle body. The bore and the throttle plate has a special coating applied during manufacture which should not be removed.

I've cleaned the center pin area where the plate pivots. No issue and improved performance.

 

Sean,

Thanks for the info on cleaning the center pin. How did you do it? Can you expand on "improved performance"? Do you mean the overall car performance, or that the throttle plate moved more freely?

 

Both should be the answer, but am waiting to see what others have to say, as i've have not done it yet.

 

Both. I had a rough idle, not terrible but when I removed the intake manifold and lifted the butterfly valve, it was black inside the throttle body.

I bought this kit:

https://jet.com/product/detail/3c898...7-01c384f82619

I started with cleaning the throttle body using the intake system cleaner and I dumped the fuel treatment into the gas tank. I had to feed the straw in carefully so the vehicle would idle properly while the can was draining.

Once done, I removed the intake again. The TB was clean. I didn't want to remove the moly compound on the butterfly valve, so I focused on movement of the butterfly valve itself by hand. I sprayed and cleaned the pivot points with a tooth brush. I also cleaned the TB where the butterfly valve makes contact with the TB.

I'd say I left 98% of the moly untouched. My assumption was, I could always remove more.

Result solved a rough idle.

I have known of others who ended up removing all of it on their fords with no issue but never followed up to see if an issue developed down the road. Ford did it for a reason:-)

 

Well, I did a careful cleaning today. I carefully scrubbed where the throttle plate/butterfuly touches the throttle body walls, as it was black with visible buildup.

I didn't scrub or disrupt areas that had visible moly coating. However, some areas of the backside of the butterfly valve seemed to have peeled off a little. Perhaps that stuff ages and is consumed by fuel vapors over time?

Reassembled system, and the car starts and idles well with no warnings showing on the dash screen. Runs smoothly on the road. Unfortunately, however, my clone Mongoose cable with V131 will read the VIN, but will not open IDS or SDD to show me if any codes are stored. I had hoped to clear the system and then monitor it live. Guess that will have to wait until I spend another eternity on the boards reading about how to make SDD/IDS behave.

I think I found the P0171/P0174 issue - one of the vacuum hoses mounted directly behind the throttle body looked to be leaking. I cleaned it, lubricated the O-ring, and reinstalled. We'll see if that problem is solved once I can hook the vehicle up to a working SDD/IDS system.