Well after much head scratching and some trial and error I finally have my wife's X-type stuttering problem solved! The check engine light came on for the first time a couple of months after we bought it in the fall of 2011.

It stayed on for the whole winter and was accompanied by the stuttering or "bucking" on hard or heavy throttle. If you stayed off the gas everything seemed fine. Once winter ended and warm weather returned, the problem went away and out of sight = out of mind.

I suspected it may be the PCV breather hose that is a common cause of the problem and checked on that first. PCV hose checked out fine, but I heard a hissing coming from the rear of the engine bay. Upon further inspection the check valve on the brake booster vacuum line was damaged in the back and was leaking a lot of vacuum.

I don't know how cheap you can find one of these, but the ones I was finding were around $75 for a vacuum line and check valve! I went to the local salvage yard and pulled a few check valves from a BMW or Mercedes or something that had comparable size and technology and spliced it in with some .55 vacuum hose. Probably $2.55 for the repair.

Brakes work perfect and that vacuum leak is gone! During inspection of the check valve I noticed another hissing (rather faint in comparison) at the 2 IAC valves on the left side of the intake. I ordered the "O"-rings from Discount Auto Parts Online -- PartsGeek.com - Domestic & Import Auto Parts Warehouse and they arrived in a couple of days for around $18 total with shipping.

Each IAC is held by 8mm bolts that seemed to want to strip (bolt head) if I wasn't very careful. The top one was fairly easy and I made sure to give a good wipe of cleaner to the sealing surface where the "O"-ring will be sealing. I used a few drops of oil and spread it around the new o-ring to help slide in and seal without binding. Screw the bolts back in and tighten them snug.

The bottom was a bit of a challenge as it cannot be removed completely without raising the intake manifold. I decided to take a chance that I could slide the o-ring around the outside and into place the "hard-way". With it being cold out, I had the o-rings setting on the warm engine to soften them a bit. I think it was a good thing and helped while stretching the bottom one around the flange side of the IAC.

I made sure the new o-ring made it safely BEFORE I yanked the old one. If the new one got damaged on the way in, I could still use the old one. As soon as both were done and tight, I fired it up and I knew it was fixed! No more hissing at all and the idle seemed a bit smoother. The true test would be on the street and it passed with flying colors!

The car hauls *** compared to before and I'm going to check the fuel mileage as we burn through this fresh tank of gas. No bucking, no stuttering, good highway passing, the best I think it's ran since we owned it. The light remains on and I will probably just disconnect the battery for a few minutes to clear that.

I am attaching some pictures for those who also might attempt such a fix. Not hard really, maybe an hour and be careful not to strip the bolts or damage the o-rings.
-Specrocz-

 

I wonder if I need those O rings too. I had the same problem with my vacuum brake hose. I think I cracked it or something pulling on it once to figure out how to get it out. Then later I bumped it with a hammer on accident and the check valve broke super easily. I went on ebay asap and found a new hose, semi-inexpensively. I noticed the brakes felt better with the new hose. Wondering if I need o-rings because my engine is making little rattly noise from that area and I don't know what it is. Haven't checked for hissing but will do that.

 

nice job bud ,

 

Thanks! I wish the winter hadn't been so harsh and I could've done it sooner!

 

Just an update on the progress of this repair. About 1-2 weeks after fixing this issue, the check engine light went off on it's own and the car is still running it's best. Just knowing that the problem was solved and the computer agrees with me is a comfortable feeling.

 

thank you for this post. it saved me thousands. thank you a billion times over!

 

The two black circular devices at the end of the intake manifold go by two names with the same meaning:
+ IMT = Intake Manifold Tuning valve
+ IAC = Intake Air Control valve

They essentially adjust the airflow distribution within the intake manifold. At high RPM / high airflow, they ensure sufficient air is diverted to the #5 & #6 cylinders, which are closest to the air intake. At low RPM / low air flow, they ensure sufficient air is supplied to the #1 & #2 cylinders, which are furthest from the intake.

On early X-Types engines, Jaguar used an undersized yellow o-ring that is prone to vacuum leaks as it ages. The vacuum leak allows too much air into the intake manifold, resulting in a lean air / fuel ratio, i.e., too much air, not enough gasoline, which can cause rough idle, difficult cold start, hesitation or bucking, etc., as well as error codes for lean conditions in Bank 1 (firewall side) and Bank 2 (radiator side).

To prevent the IMT / IAC valve leak on later engines, Jaguar used an oversized, green o-ring that better fills the gap between the intake manifold and IMT/IAC valves.

So if you replace leaking o-rings on your IMT /IAC valves, be sure to get the oversized green O-rings, not the undersized yellow ones. They're only a few $'s and relatively easy to replace.

 

Thanks for clarifying that these valves go by two names. I may not be hearing a hiss from these valves, but to be sure I don't have a leak there, should I do the carb cleaner test around the circumference of the plastic body where it seals to the manifold? Assuming I can get the car to idle long enough to spray the area, would I hear a change in cadence similar to spraying the other vacuum points on top of the manifold when they are leaky?

 

Yes

 

Although I prefer using starter fluid for testing.

 

Patterson: Yes, the IMT O-rings can be checked for vacuum leaks with starter fluid.

If the O-rings are yellow, they're the 2002 factory originals, which were undersized when new and by now are brittle and prone to leak. If they're green, someone already replaced them.

A local independent mechanic for European cars had them in stock and sold 2 for $2-3 each to me. The part number is C2S40669.

 

Hi there! I had the car idling today, engine cold and I sprayed the IMT caps, no change in RPMs detectable. I actually replaced those gaskets about when I got the car in 2010 with the green ones. About the same time I replaced the original PVC hose with the corrugated version. Have been on these forums quite some time now. Lol. It's a good community here

 

I am currently having same issue under heavy load on my 2003 x type with 2.5 petrol. Also getting code p0333 or po332. As well as po171 and po174. My question is did do slip the replacement gasket/seal over the top of the IMT unit?