As the topic implies I have a little oil leak that comes from the lower IMT ring ot my Jaguar S type, 2.5 petrol. I changed both rings, with ones from a certified jaguar dealer. Now comes the strange thing. I still have a little oil leak coming from the lower ring. What could be problem. Can it be a faulty new gasket? Or is the problem with my technician? Is there something specific that should be done when replacing those rings? Job seems easy enough. Should the two bolts holding the valve be tightened or left a little bit loose?

 

Sounds like the new O ring is pinched.

As I recall the torque was minium , somewhere around 8Nm (IIRC). Just a bit over snug.

 

It's not unusual to find a small amount of engine oil "puddled" in the bottom of the intake manifold. The engine oil gets into the intake manifold in the form of an oily mist by way of the PCV (Positive Crankcase Ventilation) hose, which pulls a slight vacuum on the crankcase (the part of the engine where you drain old oil and add new oil). It's an environmental feature designed to pull oily fumes from crankcase into the engine where they're burned to harmless carbon dioxide and water, instead of venting those oily fumes to the atmosphere.

When your mechanic changed the O-rings on your IMT's, he could have used a rag to sop up some of the oil inside the intake manifold, but probably figured "why bother, more oil will eventually collect in the same place", which is true.

I'm less concerned with the oil that's leaking out today, and more concerned with the possibility of air leaking into the intake manifold in the future. Evidently air is not leaking in today, because it would cause your engine to run rough and your check engine light to turn on, alerting you to a lean air / fuel mixture caused by air leaking into the manifold. But as these O-rings age, they tend to shrink and develop leaks - I presume that's why you had them replaced. If it's leaking oil today, it seems more likely to develop air leaks down the road, sooner rather than later.

If you decide to have your mechanic redo the O-rings to stop the oil leak today (and lessen the likelihood of air leaks down the road), make sure he uses green O-rings and not yellow O-rings. On early versions of these engines, Jaguar used undersized yellow O-rings prone to leaking as they aged. On later engines, Jaguar switched to thicker green O-rings that are less likely to leak. Hopefully your mechanic knows this and didn't / doesn't use the undersized yellow O-rings.

FYI, these IMT valves go by 2 names with essentially the same meaning:
+ IMT = Intake Manifold Tuning valves
+ IAC = Intake Air Control valves
When the engine is at high RPM / high air flow, the valves ensure sufficient air is diverted to the cylinders closest to the air intake. When the engine is at low RPM / low air flow, the valves ensure sufficient air reaches the cylinders furthest from the air intake.

 

It wouldn't necessarily run rough. Quite a big leak is needed to do that. A smaller one can be tested for using OBD - look at fuel trims.

 

Thank you for the info. The amount of oil coming out is absolutely negligible. Still, it concerned me because i just changed them. The rings are green, i am sure of it. Also the mechanic said that they snapped in place rather well. Anyway, i will drive around a few more miles and see what is the situation.