Thanks for all your information here, it's gotten me this far. I'm trying to help a friend with her 2002 Vanden Plas 4.0 76K miles. Dealer wants to replace her throttle body for $2500. Car is showing up with random "RP" and posting codes: P0712, P0714, P0171, P1642 and P1111. I've cleaned the throttle body (not bad), replaced the fuel filter, and inspected for leaks. I can't hear any leaks and all the standard vacuum connections have been pulled and checked for good seals. The car is idling rough up to 2000 RPMs, but then is smooth. Always a hesitation for the engine to rev when depressing the throttle. After looking at several of your posts, I have a few questions. MAF replacement is my first choice, but the car also has the ABS light - ASC / TRAC not available every once and a while. I was also reading that a low voltage <14V could cause this problem and others. The voltage is 13.4V, but it stays the same at any RPM. Batt and Alt were tested good at Autozone. The other thing I noticed is that there is never any vent when I open the gas cap. Is this normal? The fuel regulator line to the tank doesn't have any pulsed vacuum on it even though I have the 13.4V on the coil and the coil is good at 38 ohms. Not too sure how this operates. The intake side of the fuel regulator has a lot of vacuum, but the fuel regulator never seems to open. So any insight if the problem is her MAF, Fuel regulator, or Voltage regulator? Are there any tests I can do to eliminate either of these? From the short time I've been driving it the "RP" only shows up when your driving steady for a while, and goes away shortly after that when messing with the throttle... Thanks again for your help...

 

Changed the plugs, and bought a code reader, cleared all the codes and I've put 30 miles on it so far. For the most part it's been good, but once and a while I still can feel a hesitation on the throttle. Only code still in system is P1000, waiting for that to go away and see if anything else pops up...Found some oil in the plug well, must have a leaking valve cover. Thanks

 

Jimmy:
Back to your fuel regulator. The fuel pressure is held to 3.0 bar above manifold Pressure (vacuum). So, it's air side will have "a lot" vacuum at idle, and the pressure will balance on the fuel rail to a little over 2.3 bar or so.
Clean the MAF with MAF cleaner- It might just help.

 

Thanks Ross. I'll give the MAF cleaning that a try this W/E. I've been waiting for a code to come up and today I finally got one, but I don't think its worth anything. Along with the P1000 I got a P1642, but some threads say "I believe P-1642 is frequently an artifact of the scanner connecting to the communication system. " Plus looking at the freeze data when the code came in, the RPMs were at 0; TP @1.9%; Speed 0. Air Flow was at 399.78 GR/Sec. Does this tell anyone out there anything about my MAF? If this a normal measurement for a MAF at idle? Thanks again for the fuel regulator clarification, and the ideas...

Jimmy

 

Mick:
The CAN bus error is frequently reported by people using an AutoZone type scanner. I have seen it myself when using an ELM scanner. While I am sure there are cases of true CAN bus faults, I have never seen anyone report that they found that to be root cause of anything. Your scanner adds messages to the CAN bus to, well, scan, and these messages can interfere with the normal operation of the CAN bus, which is used for communication between control modules.
Another issue I am not sure about is whether you can get a CEL for a Jaguar specific fault. There are faults that cannot be read with a OBDII scanner that are specific to the make / model. I mention that as I wonder if you got the CEL when you had the scanner connected, or not. If you got the CEL before connecting the scanner, and the only fault was P1642, then obviously it would point to a real CANbus error.
AFAK, the wheel sensor cannot cause a CAN bus error- It will result in an ASC / TRAC not available in the message panel.

 

Thanks Mick and Ross, I did clean the MAF today and the problem got much better, but it still randomly has a slight hesitation when the throttle is applied. I will clean it again, then if that doesn't work I will ultimately replace it. Anyone know where the cheapest place to pick one up is? The MAF comes apart easily, but when I look it up on the internet, they only show the entire unit with the MAF installed. The numbers on the MAF are Denso LNE 1620CA (197408-0010).

Thanks again for your help...

Jimmy

 

Jimmy:
If you have really checked all of the normal vacuum leak spots (full load breather tube, partload breather tube, plastic inlet plenum, brake booster line seals) then yes, I would guess the MAF rplacement makes sense. Can't help with a source, but please let us know your results!
BTW, I am pretty sure one thing that can trigger RP is lean burn. That would also point to MAF.

 

I've pull all those points apart and looked for cracks or bad o-rings. Also sprayed cleaner on them with the car running to hear any changes in the engine. They all seem tight so I guess it'll be a new MAF. Thanks again for your input.

 

let us know if the new MAF fixes it Jimmy. I've heard that more than one time.

 

the p0712 is trans fluid temp sensor fault,usually the harness inside the gear box,the other issue is with the can communications,not sure if the generic scanner would caused that but it sounds like it could,ask the dealer to give you a print out of the faults from you last visit,it should be on file