My XJ8 2006 almost dies when drawing to a stop. This gets worse if the AC or rear window defroster is on. The same thing happens if I turn the steering wheel or when AC kicks in with car idling. The car has not died yet but it comes to the point of bad stuttering before ECU bumps the idle up. I am thinking it is the “Idle Air Control Valve” that is bad(slow) – Can anyone confirm this or give some inputs. Is it possible to clean the "Idle Air Control Valve"? - what is the price of a new one? I was thinking to use the 3M intake cleaner which I would think would clean the IAC.
(I have checked for vacuum leaks but there are not any apparent ones)
Thank you in advance
MTW

 

Hmmm, on my '06 I have noticed a rough idle sometimes. Never to the point where it almost stalls, though (drops down to maybe 300-400 rpm). I consider it a feature, not a problem.

Although mine never tries to stall simply when coming to a stop. How many miles do you have?

BTW I just came from a Lexus LS400 ('97) and those cars had a complicated power steering system where it was connected to the air intake. When you turned the wheel, somehow it would keep idle nice and smooth. Unfortunately this was a huge failure point for many an LS400 and the cars would suck up tons of power steering fluid and also leak all over the accessory belts and alternator. I am thankful the Jaguar doesn't seem to have this kind of system!

 

There is no idle air control on your XJ. There could be a possibility you have a bad throttle body. Any faults? Any lights on?

 

Jaglover922 you are completely right there is no idle air control valve it is fly by wire system. There is no codes or lights. My XJ has 59000miles on it. amcdonal86 my idle also drops to 300-400rpm which I consider not far from stalling - normal?

 

I don't know, I consider it somewhat normal. A couple times, though, I have started the car and it has idled rough for a few seconds before finding a stable idle speed.

It usually only goes down to 300-400 rpm if I am turning the wheel at a stop, though.

 

Look for air leaks, since the engine is 'sealed', any small outside vacuum leak beyond what the engine needs thru the TB and MAFs, it'll reduce the idle speed. You could also clean the MAFs and heater wire also, perhaps dirty enough to affect airflow readings?

Just spitballin...

 

I had rough idle and it turned to be a vacuum leak from the air intake at the throttle body. Check if those intakes are clamped tight.

 

My 04 had similar problems. I had throttle body cleaned and a pressure test on the fuel pumps. Fuel pump was failing. Pricey - 700+ for a L fuel pump but the problem is gone.

 

Fuel pump at 3.5 yrs seems less likely than a vacuum leak or dirty MAFS, looking forward to your resolution.

 

Cleaned the MAF and checked for vacuum leaks but to no avail. What heater wire are you referring to?, h20boy
Can I use the 3M intake cleaner for cleaning the throttle body? or can I just spray the cleaner directly into the throttle body - how should I clean it?

 

Noticed this morning that when braking the transmission kind of was slow shifting down and pulled down the idle before shifting to 1st gear - any idea( The temp was 10F so I was slow too)
I have cleaned the MAF, sprayed all hoses with the engine idling - no vacuum leaks- don't know how to check if brake booster leaks - any idea. Does anyone know if it is advisable to at all clean the throttle body? - I read on the internet that the TB has a special coating and should not be cleaned?
Since this is a fly by wire system how do you make the TB open so you can clean it? will it open if you turn the ignition to on?
Hope someone can help I would really like to fix this low idle issue.
Thank you in advance
MTW

 

This is an excellent guide to TB etc. cleaning. (with excellent pictures)

http://www.maxperformancecars.com/dm...Clean_MAFS.pdf

Good luck

Bob

 

Thanks Bob,
That is really a very thorough guide - all set
Martin

 

the transmission does get a little help in shifting thru vacuum lines to the TB I think. If you are uncomfortable doing a TB cleaning yourself, ask the dealer for their 'fogging' service. Any chance its still under warranty?

 

also, did you by chance replace the air filter, just for grins?

 

Air filter is changed and it is out of warranty. I am not uncomfortable cleaning the TB myself - just a lot of clean microfiber rags, TB cleaner and noting but the rags and your fingers. I did considered the 3M intake cleaner because it will clean beyond the TB - I assume the fogging service is that.
Thanks

 

Don't use any solvent other than kerosene cleaning the throttle body, it is coated and it can be damaged.
I think your problem is a problem involving the transmission communications system. There might be a CAN network problem with it not communicating well. Try locating the CAN connectors between the TCM and the ECM and cleaning them. You might consider getting it to the Dealer and be sure the Tranny has the latest software adaptations, There have been some updates and you need them if they are not in there. The Dealer would know based on your VIN.

 

I meant to say to check the TB connections as well, in addition, a bad throttle position sensor could cause this and it is a probelm with these cars.

 

It says on the CRC throttle body and intake cleaner that it is safe for coated throttle bodies. I don't experience any of the typical bad TB sensor symptoms so I don't think it is that - but maybe it is I will check the rest before going there - there are no codes. I will definitely clean all electrical connections - that is very possible.

 

Cleaned the TB - I did it just with a damp cloth - carbon .
came right of - was not very dirty. Checked for vacuum leaks -none. Cleaned and primed all connections in engine bay. Test drove the car - it still does it -, slow at correcting when strain is applied on engine, whether it is AC, power steering or a fast stop.
The car has never stalled just rough idle for half a second until idle is bumped.
I will consider this a feature and not a problem (until maybe it throw a code one day) It has always done like that since I got it soon 16000miles ago - only code was when temp sensor housing went bad. Thanks for all your suggestions and help - I will let you guys know if I one day actually finds a remedy for this quaintness
Martin