Hi Mac...
Saw yer post from last month...
This is way wierd....My name is Mac too,and I gots the same problem with my
90 Miata.
Started about 3 weeks ago.....always had a little dip in power around 3800
rpm....so I went and got a KN air filter.
Things were OK for a week,then ,really very quickly,started losing lower at
low rpm.
I have since>>>
Replaced plugs and wires and fuel filter.
Had timing checked,all good,compression checked(all about 150,very good),
Exhaust system clear(can see through cat converter too,very good),
Air sensor traded out,even
dumped a bottle of injector cleaner in  it,no change.
All in all,about $350 spent,and still no better.
Going through way too much gas too.
Tail pipe showing alot of black,seems to be running very rich,but plugs are
clean,and don't look like they are carboned up at all.The only code that
came up when we plugged it in was about t the crank indicator sensor,but
that may have been a result of when we did the compression test.
My question to you is,did U find anything else with yours?I am running out
of ideas.
I am getting the injectors cleaned tomorrow,but really don't expect
much(ya...am getting a bit P-O'd.....so my expectations are dropping.)
What it feels like when driving is like it's got something blocking,either
air or fuel...and sorta like it just won't blow through,y'know?
Any solution U might have come up with would be appreciated.
( the guy who responded to your post said your wires were the problem,and I
replaced mine...did U?)
Thanx
Mac

Please report that you do in fact have a 90' that HASN'T had the dreaded
disolving crank keyway. Loss of power similar to the spark plug wire
symptom is a tell tale sign. Check to see how far off the the timing mark
is from top dead center by using the dip stick in number one cylinder
trick. (timing retards beyond advance of crank angle sensor adjustment-
no way to get timing correct until crank is fixed) Miata.net of course
has all the particulars in the garage section.
good luck from a fellow 90' owner.

Look at the crank pulley when the engine is idling. Does it wobble? If
so, the crank nose is probably failing. The loss of power is due to cam
timing drift.

A junkyard. An average used 1992 or 1993 engine with less than 100k
miles on it should extend your '90's life for years. The crank was
redesigned partway through the 1991 model year.

However, many owners have had good results repairing a damaged keyway
with Loctite. If it works, you will have saved a bundle; if not, you've
only lost a few bucks and a couple of hours. See miata.net for all the
gory details.

Don't get overwrought about crankshafts until you've diagnosed your
problem, though. It might be something less dire.

Was wondering if I might "pick your brain" as to how difficult the Loctite
fix was.  I'm just a weekend garage mechanic and I'd appreciate your
thoughts on any potential problems you encountered.

Jeff
'90 Red