So, I pulled the intake manifold to replace the coolant hose. I used new gaskets. JTIS says to torque to 22Nm or 18ftlb with no torque order. I torqued from middle to ends in two steps, so unless I somehow calculated ftlb incorrectly, I don't know why there would be a problem.

Also, in order to take the manifold with the throttle body attached, I had to pull the injectors/rails. JTIS says to replace the o rings, but the dealer didn't have any. So I cleaned and replaced the gaskets. They seemed okay to me, but I'm wondering if that is also a possibility.

And, the last thing is the vacuum line off the back of the manifold to the brake booster. It seemed loose but I'm assuming it is normal. I didn't think the brakes felt any different, but I was thinking of disconnecting it, plugging it, and seeing if the brakes feel substantially different.

Anyway, I am thinking it is one of these three; any recommendation as to which it might be, or is there something else that is a coincidence and something else is wrong?

Thanks,

Gordon

 

Gordon, check all your connections (hoses - including plastic hoses) from the air filter to the throttle body. Take off the engine decorative cover and check each one. One time I found a disconnected hose right under the decorative cover - never would of suspected - engine purring like a kitty - no vacuum noises but P0171 and P0174 - could also be that hose by the brake booster you mentioned also - shouldn't be loose.

Hope this info helps.

 

That brake booster hose should be tight, I agree. There is a little o-ring in the TB...take a look at these pics. When I did my intake, I only removed the o-ring and replaced it...leaving that brass insert alone, as I had no idea how to remove it. As for the brake booster line, its like a chinese finger trap...keep the black plastic 'gripper' pressed against the TB while wiggling the line out. The o-ring is inside that brass part..and likely hard/brittle..and no longer sealing

 

Matt, thanks so much for the pix! Quick question. When you say the brake booster hose should be tight, are you then referring to where it connects to the back of the intake manifold? You mentioned TB above, so not sure if the picture is of the back of the intake manifold where the brake booster hose comes out or part of the TB. Then again, you've got SC and I'm NA, so could be a completely different animal.

So, if I'm understanding correctly, you hold the plastic insert against the intake manifold while pulling out the hose (your picture). Anyone know if it is possible to do that with the intake manifold still on the engine? Since I have everything reassembled, I'd HATE to take everything off again (the reason why I didn't take everything off is because I was having a hard time removing the last connector on the back, so I just moved the manifold out of the way to replace the coolant hose). But if I get the hose off, does that black sleeve then come/fall out? And are you saying that the brass fitting screws into the intake manifold and the o-ring is inside that? If so, then of course there's no way to get that o-ring out and replaced without pulling the intake manifold again since I won't be able to see the o-ring, let alone get something in there to pull it out. This is looking more and more like a complete redo. If so, I'm assuming I need to get new intake manifold gaskets again since they've been torqued once.

 

Yes, you should be able to reach that with the manifold still on the car, but your access will be limited. Removing the return line to the EGR valve just below the TB on the backside may give you more finger room.

These pics are from my 03 XK8...the N/A engine, and the pic is at the TB itself where my brake booster enters. good luck!

I mean tight as in you can barely move it around at the TB if the o-ring is holding it tight. before I changed mine, it had some play in it.

 

So, even if I can pull the vacuum line out of the manifold, if the o-ring is inside the fitting on the intake manifold, how is it possible to remove and replace it. I'm hoping there is (it would be nice if the o-ring came off with the vacuum line, but that would be too easy...).

 

I got mine out with a little twisted-tool like this.

Its just inside the brass fitting, about 1/2 inches back from the edge, so you can under it with this tool, and pull it out...replacing it you must be careful to just get it in the groove inside the brass fitting, else you'll be taking your TB off to get it out from the bottom.

 

Stopped at the at the dealer to pick up the o-ring/brass insert/plastic slider. I talked to the chief mechanic and he was saying the same thing; it is possible to do, but not easy, especially to put the new one in. I told him I was thinking of just cleaning up the area with brake cleaning fluid, getting some high temp silicon sealant and sealing the hole area (rather than risk having to take everything back off again either to see what I was doing or risk dropping an o-ring inside. Then the next time I need to pull the intake manifold, just peal off the silicon and do a proper replacement. He said if it was his car, he'd do exactly that! Got a stethoscope on the way (used a hose in the past but not too good), so I'll confirm the leak is there (or find out where it is) and if so, I'm going to do that. Yes, I'd prefer to do it right, but it is WAY too much work to pull everything for just that. Plus, the service manual should say (or maybe I missed it) that you should check and probably replace that o-ring every time you pull the intake manifold off. Not listing and recommending replacing all associated consumables is bad information.

 

Hate to say I'm ready to give up and take it in, but I can't find the vacuum leak. I got a new automotive stethoscope and listened around the brake booster vacuum line both at the intake manifold location and the connection heading to the brake booster, but could not find (hear) anything. I checked the other locations around the manifold where there might be a vacuum problem, but couldn't find anything. I'm thinking I'll check the torque on the manifold bolts, but since I get the same error code for both banks, I figure it has to be upstream enough that the same leak affects both banks (both error codes keep coming up).

The display says "reduced performance". It seems to run fine unless I hit the throttle too hard or at too high RPM; if so, then it starts cutting out (maybe some cylinders are not firing--I assume this is how "reduced performance" works.

Anyway, been very busy so little time to spend on it, but I'm tired if it so ready to take it in.

Any ideas before I punt?

 

Okay, we can close this thread. If I had done a better job of following Abonano's advise, I would have noticed the crankcase ventilation hose that goes to the plastic molded part that attaches to the throttle body. But out of frustration this morning, I went through the intake manifold removal process and made a list of all vacuum or TB related items, then went out and checked each one. This one wasn't on the list, but as I looked around, I saw this out of the corner of my eye. Granted, I wouldn't have expected that it would have any impact on this problem since it is before the throttle body, but since the Jag now lays a long strip of rubber with DCS off (no more reduced performance on the screen), it looks like it was it. Now I can go back and write up the procedure I used to remove and replace the intake manifold.

Thanks to everyone that helped with this.

Gordon

 

Spoke too soon. Same error codes again....

 

Gordon - check each plastic connection for any cracks or not sealing flush - these plastic hoses are very susceptible to cracking...

 

use some MAFS cleaner and monitor the fuel trims live as you spray methodically. T hat's how I found my leaks on my xk8. Throttle body gasket, manifold mounting bolts/sleeves, and a couple lines at the Norma connector (dried up o-ring)