Hi all, first post here.

Recent new owner of a 1998 XK8 convertible. Car was in good condition when I picked it up about a month ago. There was some coolant seepage near the original plastic thermostat housing, so I decided to tackle that job and replace it with the new aluminum housing. After trying repeatedly (and failing) to remove the rear bolts of the thermostat housing, I decided to remove the intake manifold in order to properly access the thermostat. Removed throttle body and intake manifold, replaced the thermostat housing, replaced the 8 gaskets on the intake manifold and the gasket on the throttle body with new.
After buttoning up everything and refilling the coolant, I crossed my fingers and started it up. She started on 2nd try, but there was a distinct air leakage sound coming from the the drivers side, forward part of the intake manifold. Sounds like a suction sound. Along with that, the idle very rough. Got a Check Engine light, and it threw 3 codes (P1336, P0340, P1000). I discovered that I failed to reconnect the multiplug located on the bracket under the left side of the throttle body. Reconnected that plug, but still have the air leak and three codes.

Any ideas? My first thought was to spray a little water around the area that I heard the leak, and see if the water temporarily seals the leak and improves the idle. If it does, then I can start isolating what might be the problem. I also thought that when I took the manifold off, maybe one of the fuel injectors was unseated and is leaking around it's seals. My other thought is just to take the manifold out again, check the seals, and try to reseat it. But if there's another option without getting that all out again, I'd like to explore that first.

Thanks in advance for any ideas.

 

Go back over your work and reinstall the inlet manifold. It's possible one of the runner seals became dislodged when you were installing the manifold.

 

NBCat, by runner seals, do you mean one of the eight seals between the intake manifold and the engine?

 

Yeap 8 runners and 8 seals.

 

Yes, that is correct.

 

Follow-up on the mysterious air leak.
Took off the intake manifold again. Cleaned all surfaces, checked all seals, carefully reinstalled it. Started it up again, and still had the air leak! Took a little water bottle and sprayed near the area to see if I could pin point the source of the air leak. While I was poking around, I found that this breather tube was completely busted! I used some silicone tape to wrap it in the meantime, and the leak disappeared! Problem solved. Now I can finish the original thermostat job! Thanks for the input.


Broken breather tube is highlighted

 

That is the PART LOAD breather tube. It runs from there underneath the intake manifold to the base of the throttle body and from there to the evap canister. If it sealed sufficiently and doesn't throw a vacuum leak code you will be ok. If it does SNG Barratt carries a replacement part # AJ84880