All;
When I start the car on cold startup, the engine runs very rough until the fast idle reduces below 1000 RPM. After that, engine runs very smooth.

Any ideas as to the reason.

Cheers

 

How old is the gasoline in the tank?

 

Sticky valves/weak valve springs would cause something like that. Once the engine warms up, the symptoms disappear. This is one (and probably the worst) possibility out of many.

 

This had been plaguing my 04 XJ8 for the past few weeks. I have tried the search for vacuum leaks and even replaced a MAF with an autozone part to no effect. I notice that cold, it runs very rough until it starts to warm up. Once the car is warm it runs fine. Also, after first start the car seems to start smoother and again, once warm, runs as well as it ever has.

It has set P0171 and 0174 codes in the past while exhibiting this behavior, even with the new MAF. I gave up on the Autozone MAF and put the original (I don't think it is a Jaguar OEM) back in. Currently, after resetting the codes, it is not setting any codes but I think it is a matter of time (not enough cycles).

What I do notice is that the Intake Air Temperature is reading high. I tested tonight at an ambient temperature of about 68F that the Intake Air Temperature is reading 91.4F. Just as a crosscheck I ran the same test on a 01 Toyota 4Runner that has a similar MAF and the Intake Air Temp was never more than 71F.

I am guessing the IAT is taken from the MAF since I cannot find a dedicated sensor in the workshop manual. I could see if the computer thinks the air temp is a toasty 91F and it is really much cooler it could run the engine leaner than it should causing a rough idle at cold start-up.

Hope this helps the thought process and starts a dialog re: possible solutions.

 

mbwillgrubs,

(I am guessing the IAT is taken from the MAF since I cannot find a dedicated sensor in the workshop manual. I could see if the computer thinks the air temp is a toasty 91F and it is really much cooler it could run the engine leaner than it should causing a rough idle at cold start-up).

This comment makes a lot of sense.

What I think I'll do is remove the MAF (knowing I'll more then likely get some codes), tomorrow morning to see if maybe the IAT registered will be cooler and see if I get the rough running at start up. Will post results.

Cheers

 

First thing I'd do is scan for trouble codes. Don't guess at anything.

Pending the outcome of that, the second thing I'd do is inquire with a Jag dealer about having the ECM flashed, this is a known problem - see http://www.revbase.com/BBBMotor/TSb/...dPdf?id=143065

Don't take anything apart or spend a penny on parts until you've done those two things.

Removing the MAF is pointless. Use a code scanner to read live engine data values. I have this one, it's pretty solid http://amzn.to/2gLOOs3

For what it's worth my 06 XJR has a rough idle on cold startup sometimes.

 

I agree that it is important to look at what codes are being set. In my case it was the P0171 and 0174 lean codes. I am using a OBDscanner on my laptop. I have had this set the codes a couple of times now and am just posting for assistance.
My car would not run with the MAF disconnected for what that is worth. Are you reading the data with something (or how can you determine IAT)?
Wrt the ECM flash; I did notice that was a TB released in 05/06 (thanks for the info btw). What do you think the probability one of the previous owners did not have this performed and is there any way to check (probably not, huh).
I still would like to know if erroneous IAT would cause fuel delivery to be altered. My counterpoint to the argument is that the computer may make that decision based upon coolant temperature and that is reading normally.
Again good luck and thanks for the replies.

 

If IAT (or other sensor) reads plausibly but is wrong you can get bad fuel/air mix and misfires.

IAT is often in the same housing as MAF, but actually is separate. May well have to replace as a unit.

 

That would be my impression as well and yes the MAF houses the IAT along with the mass sensing component.
This begs the question of what would be different about buying MAF units from various vendors. Rock Auto sells 3 or 4 units from different suppliers ranging from ~$40 to $70 for the Denso version. Of course the Jaguar unit is $200+ that still comes from Nippon Denso. The nomenclature is different for all the devices including the Denso units.
Something like the IAT which is probably a simple thermocouple I can see no reason for difference. But would the mass sensing units (thermistors?) be different and/or the circuitry in the MAF itself be calibrated for a particular car.
I have read in the forum that members have had success with Autozone (DL-3000) parts but others only have success with the original Jaguar component.
Any thoughts?

 

Or even a used one from wrecker/breaker/ebay.

I suppose a clone may be badly made / wrong transfer function(s) / etc or of course it may be fine. Interesting gamble.

I think I'd get a used one but YMMV.

 

All:
Took off the present MAF, an Auto Zone one and replaced it with the OEM (I'm guessing, no way to prove it's the OEM, it's a DENSO I believe) after cleaning it with cleaning fluid. I believe I changed it because I was getting an engine light while running.

Started her up and no Rock and rolling. Smooth as a babies butt.

But being an old fart, will wait till three or four cold starts and see what happens. Will post if it starts up with the rough happenings again.

Thanks to all for the suggestions
Cheers.

 

Sounding good so far - hooray if it stays that way!

 

Just a wild guess- are you driving the car until it's fully warmed up between each start? Many owners who start the engine just to shuffle cars around the driveway report rough running upon subsequent re-start.

 

That is cool. I don't suppose you could send a picture of the markings on the MAF. The Jaguar unit is a Denso but with specific coding on the top.
Where did you purchase said unit? You said you cleaned it so I assume used but you know the assume thing.
Mikey: No, usually gets a good drive around and is warm before shut down. It has been almost 80 here in the Houston area and it has not been too bad. It is supposed to drop to the 30's tonight so we will see what happens. It will test my IAT failure hypothesis. I am guessing that as the temperature drops it will be too lean for the ambient temperature conditions and the rough running condition will be exacerbated.

 

All:
Took an excellent picture of the MAF, but can't seem to up load same from my IPhone.

This has always been a problem for me. Try to follow the instructions and get nothing.

Oh well, what it says on the MAF top is: 040510. in an outlined box it says: 1X43-12B579-AB, NEXT LINE :MB197400-3021, NEXT LINEENSO, THEN: Made in Spain.

I'll keep trying on the photo.

Cheers

 

1X43- often indicates an X-Type part. (May well be shared across models.)

 

Ordered a new OEM today. I will post again to tell you if it helped. Chuck, the markings seem to be from the original part. I went new just so I could not deal with this again for a while. Thanks for the input.

 

mbwilgrubs,

Don't blame you. Although more expensive, you'll more then likely have less headaches down--the road.--pun intended!!

If this one I just re- installed fails, I'll take the same step.

Cheers

 

Mikey---

Nope, always let it warm a little before driving. I guess it's a hang over from the Radial Engine days of my past aviation days...........