98 XJ Tap/Knock at Idle - goes away at throttle

[831_xj]

Its all fun and games until you drop the tranny and find it is indeed not cracked...

I have had the same exact knock for 20k miles.
I'm suspecting bent valves due to a broken or weak valve spring to go along with my cyl 1 misfire. I'm no engine guru so I'm just waiting to break and then I will drop the cash to build a 4.6L stroker. Sometimes it will miss like hell and shake. Other times its smooth as butter.

Look for a popping sound in the exhaust maybe

 

[RMSLLC]

Well my "new to me" xj that is tapping at idle has a broken #6 piston skirt.
We found pieces in the oil pan. Sounded exactly like a lifter tapping. Only made noise at idle.

$600 engine from the salvage yard with 130k miles on it, and $500 labor at the shop and im back in business.

 

[CodyScott]

Hey, I wanted to join this group because I had the same problem with my 91 XJ and I found out the problem. I replaced the main bearings and rod bearings and it still knocked. After many days of trial and error I now have an almost rebuilt engine...lol

But the actual knocking noise came from my tongue converter bolts being backed out. Pulled them out, put some loctite on them and put them back in (one at a time) and now she hums like a sewing machine. So good lucks guys!!