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HI, I bought my 92 v6 mx-3 at christmas.
It seems a bit slugish sometimes (weird).<p>I'v noticed when I rev it up high 4.5K+ it sounds realy rough like a bag of hammers & lots of vibration through cabin. It's done 107K miles.<p>Is this just worn engine or could it be timming or ignition probs (changed plugs, ngk 1.0 mm gap).<p>or should I look 4 new engine or a 2.5L swap <p>Thanks all

I'd suggest doing a basic tune-up (air and fuel filters plugs wires cap rotor) to start. You could try just ignition wires and plugs. They can sometimes crossfire at high revs if they are old. Your Camshaft may be worn, (compression may tell this if it's worn enough to prevent the valves from openimg fully). You may have some debris in or on your mass air flow sensor(clean it with compressed air, but gently). Oxygen sensor, but that usually shows up at idle. Blocked air filter. Gas filter or fuel pump may be titters, or fuel press regulator.
I think the tune up in stages would be your best bet then you will know what the problem was. Make sure you do new plugs before you buy wires. May save some $$$$. If you don't know when the last tune-up was none of these things will hurt anyway. Your engine is probably not baked though if it runs smooth at low rpm. Oh yeah, Does it smoke? That'd be a different story.
Good Luck.