OK, would any body be able to tell me what code P0442 is? It is probably related to the rough idle on cold start. (I found mention of this code in another thread, but it was not identified). Car starts right up and runs smooth for a few seconds, then the idle drops down below 1000rpm and is rough for a few seconds to a minute, then smooths out. Thanks in advance

Edit: Oh I guess it might help if I mentioned this is an 07 XKR

 

It's an EVAP small leak. Might be a loose fuel cap but suspect any of the tank/purge/etc stuff. Rough because vacuum is changing unpredictably so PCM struggles.

 

Weird; I can't find P0442 in the 4.2 workshop manual, but as JagV8 says, the 5.0 manual says it's an evaporation control system leak. Diagnostic actions:

 

This forum, you guys, are going to make owning my first Jag a lot easier to deal with. I might have above average mechanical aptitude, however, I am certainly no Jaguar tech. I bought the pdf of the manual, but could not find P0442, and have to say, if all Jag manuals are written this ambiguously and convoluted, it is amazing any of us can work on them without just doping off the car and our paychecks at the dealer. I am in the San Francisco bay area. We have four dealers within a 50 mile radius. All have terrible reputations for misdiagnosis and being very proud of their parts. Need to find a good independent shop for when I find things I am unable to tackle myself. I saw a thread asking that question, I subscribed, but no recommendations.....
Thanks again for the help gentlemen. You remain my best option.

 

The biggest PITA, as you can see from the diagnostic actions, is that a lot of stuff requires (or is made a hell of a lot simpler by having) the proprietary Jag diagnostic system. There are some third-party OBDII readers that work with 'semi-official' outdated versions of the Jag software, but the whole thing is a bit too kludgy for my liking.

 

Yeah...at least the five digit code gets me in the neighborhood. I hate the thought of paying the dealer $120 to tell me I need to replace my air cleaner.

 

Turns out it was the DMTL pump. Dealer quoted $1090...Ended up paying an independent shop (Bacchus British in Dublin CA) $618. Considering where the thing is, I'm ok with that. Thanks guys.

 

Glad you found the problem! What is a DMTL pump and what does it do?

 

Its part of the EVAP (fuel evaporative sysyem) sits above the differential by the charcoal canister. If I understand correctly it puts a very slight pressure in the fuel system and somehow self tests for leaks. Not too uncommon to fail. Problem is it is a real pain to get to, from what I've heard you have to move the diff out of the way to access.

 

DMTL = Diagnostic Module Tank-Leakage. From the manual:

 

It's baaaaaaack. Okay I had five days with no MIL, the rough idle on cold start was definitely worse. But now the MIL is re-lit (code P0442 again). So I know the DMTL failed a self test. It was replaced and now it does not fail the self test. The rough idle on cold start is worse. So with my limited understanding of the EVAP system, it has to be something between the DMTL and the purge valve (that was supposed to be a question and not a statement). Other info that might be pertinent: I purchased this car two months ago, 07 with 9k miles. It sat for a year prior to purchase. It still runs like a bat out of hell. I am a Sagittarius with blue eyes and my favorite color is blue.

I am planning on leaving on a trip tomorrow (750 mile round trip) and was looking forward to driving the car. Take the car? Don't take the car? Ignore the MIL until I get back?

 

Maybe they didn't install it correctly, or damaged a seal during installation, and a small leak has developed. I'm not sure how this would relate to the rough idle, though - that sounds like a coil or plug problem. But I'd expect to see some DTCs relating to the misfire coming up on your code reader.

It may be time to get a dealer to check the codes, to see if anything else is showing that your generic reader isn't picking up.

But if it's running OK once it warms up, it's probably fine for a road trip.

 

Correct, no rough idle when it warms up. Great power, great fuel economy. My gut says it's ok to take it on the road trip, now that one of the gurus concurs, I'll worry about it when I return. Thanks Ngarara

 

Enjoy the trip - but make sure your AAA membership is up to date, just in case

For future investigation, one source of rough cold idling is a break in a wire that closes up when the engine heats up & the wire expands. I had a problem like that in a plug lead once - it was a bugger to find. It will really help a lot if there's a code indicating "misfire on cylinder 3" or some such, so you know where to look.

 

Take the trip. This is a very minor code and does not affect anything but evaporative emissions. Just be aware several people on the S Type list have chased this one for a long time.

As JagV8 said this is a "small" EVAP leak. There are also codes for the large "Evap" leak which is MUCH easier to find. Many times the P0442 is a failed gas cap or a not proper latched fuel cap. Have you checked this yet?

It may take a dealer to do the smoke test to find it. From what you posted I think they just changed a part on you and did not troubleshoot it completely.

Can you take it back to the mechanic as the repair is so recent? I think it's his responsibility. With $618 at stake I would sure bring it back.

I would like see a picture of the part they changed as that is not on the earlier cars and I was unaware it was added.
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Ohhh yeah I'm bringing it back to the same dude as soo as I get home. And he better hook me up. Yeah, first thing I did was check the cap was on tight (I don't have a way to vacuum test the cap, but I know they do that when they're smogged). Yeah, this is sounding like it has smoke test written all over it.

 

I've had the same 0442 issue for over a year and it seems to come in spurts. I'll go a month or so with no codes and then for about a week I get the code on almost every start. My OBDII gets a workout those weeks. Car runs fine.

 

Okay so last Thursday the 0442 code came back. Friday morning I cleared the code before heading to Oregon to visit mom (700 mi round trip). Code has not come back? Prior to replacement of DMTL it would return the next time I started it (or definitely within 3 times). I guess I'll just have to see. Might be like TFlan says...just gonna be something I chase.

Car ran fan-freakin-tastic. Wow.

 

If it keeps coming back, I think you have a case for asking the Bacchus people to take another look, because they clearly didn't test/diagnose it fully. Just changing the DTML pump hasn't solved it - in fact, it may not even have been necessary. Ask them if they smoke-tested it, as they should have done.

 

Read post #10 as to why this code might take some time to come back. The problem might be there for quite a while and not show up til the requirements are met for the car doing a test on the system.

I had a car with this code and had to drop the fuel tank to tighten up a vent line clamp on top of the fuel tank. Not a Jaguar though.