[T3] Weird Idle Dips

[Gary Forsmo]

A question has been rolling around in my head for several months.

During 2011 summer (Jim A.) went through a tune-up procedure on my
'69, 1600cc, FI, MT Squareback.

Jim's comment:  So I've just gone back to the W8AC or W8AP.

He replaced the spark plugs with (I think) W8AC plugs.  In the process
of installing the SP's, he thought he felt a cross-threaded, spark
plug situation on either #2 or #4 cylinder ... I can't remember which
(maybe you do, Jim) ... when he screwed in the new SP.

He suggested, at some time in the future, that spark plug hole/bore
should be inspected and corrected if indeed the threads were messed
up.  The engine seemed to have operated fine for the entire summer.
The car was stored away (and still is) for the Wisconsin winter.  That
leads me to believe when the new spark plug was screwed in, the SP
went into the correct threads, seated on the copper washer properly
and tightened to the correct spec of 22-29 ft. lbs.  Operation seems
just fine.  Or maybe not?

Which brings me to my question:
IF (big IF, here) indeed the spark plug hole has been cross-threaded
at some time in the past, what is the correct remedy?

While reading about HeliCoils, I came across other metal inserts to
repair spark plug holes.
E-Z Lok, http://www.ezlok.com/InsertsMetal/carbonSteel.html  &
Time-Sert.  http://www.timesert.com/html/sparkplug.html

Has anyone (and Jim and others, you can jump in here) used either E-Z
Lok or Time-Sert brands of these solid steel inserts?
Results?
Ease of installation?
Longevity?

The more I read about HeliCoils, the less I like them.  Special tools.
 Staking the coil.  Unscrewing.  Screwing further into the bore. Etc.

Gary "Frito" - '69 Variant, FI, MT
Rockport, TX (winter)
Lake Geneva, WI (summer)