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Did you try to swap the existing tensioners to see if that solved the issue?

I did an oil/filter change yesterday and swapped both of the easily accessible tensioners. Noise is gone. The single circle (IMS tensioner) was in the double circle (cyl 1-3) location and there is obvious wear marks on it. Both are now installed in the proper locations and I have the 3rd for cyl 4-6 but will do that when I drop the motor at 200k and do chain pads..etc.

Oil was perfectly smooth coming out.. Motul 5/40 with about 4500 miles on it.

the plot thickens.. I'm absolutely sure that the tensioner in the 1-3 location was the culprit for causing the startup rattle. The friction marks on the hydraulic piston where it was worn out and contacting the body of the tensioner confirms that. I'll take some pics of those pieces eventually.

I am also pretty convinced that the rattling I heard while the car was running at idle (more of a knock) was the alternator mount cracking and moving around. The sound was centered to the left side of the engine bay, and I couldn't pinpoint it. Well with a new alternator bracket from the 997, and a new alternator in place, the rattles are now ALL gone.

But.. there's always a but. I have a hissing coming from the same area now. I suspect one or more of the large vacuum hoses on the left side, although with Darth Vader (K&N intake) in my right ear it's very hard to pinpoint. Took the 996 out for some errands yesterday and she was great, but on the way back home I popped a CEL. 1124/1126. Severe lean condition, most likely an air leak.

I have been poring thru the 996 FSM and I can't find a diagram of vacuum lines and larger air hoses. I suspect that the one leaking may be the one connected to the throttle body thru the approx. 6" long sensor with attached hose. I'm trying to figure out where the other end of that hose, and also the clip on smaller hose from the air injection valve terminates at. The smaller hose feels loose..

Going out in a few to dig out the stock airbox and reinstall to get the Sith lord out of the equation and I can try to nail down this hiss and order up the proper parts.

any help much appreciated

Get a smoke machine to make your life easier. You should still ditch the K&N atrocity, but leaks can be notoriously hard to find without help.

Real machines for automotive use are $$$, but I found this which looks like it could double for some other McGrubber uses... http://www.taurusclub.com/forum/83-odds ... chine.html

that's awesome DBJoe.. I guess I just need to ask Google the "right" question.. Thanks!

I think I may have solved it. The attachment for the brake booster hose, 2 10mm threaded screws into the manifold.. there is an o ring on that when you pull it off. Mine was shot. Dug into the old harbor freight o ring kit and found a replacement. Then reinstalling it, discovered the coarse thread screws were not tightening.. stripped. Went into the magic bolt box I've kept for the last 25 yrs of stripping cars into race cars.. and found a few that were a few mm longer to use.

I disconnected the battery to clear the DME and get a fresh start, and she idled a little lumpy, burning off the previous richness for a bit. She'd clear her throat well though with a minimal hesitation, but finally it burned off and settled out. On a test drive she was much smoother and idles well now. I just got called into work tonight at 6:30 so I'll take that 40 mile round trip to eval it..including the 630a cold start.

stay tuned