Hesitation upon hard acceleration?

[magnumtoy]

Have a little problem with my '92 Mazda 2600i, maybe you guys can help.

History: 170k miles on it, last few years now only driving low miles, very infrequently. 2 yrs ago (maybe 15,000 miles) changed plugs, fuel filter, dist. cap and rotor just as prev. maint. Ran fine.

Just recently, engine seems to bog or hesitate pretty bad at lower rpms when i really step on the gas hard. But once I get upwards of 2500 rpm it kicks in and takes off/accelerates fine. Also, when cruising in a gear and step on it hard, it bogs and then again will catch around 2500 rpm and then kicks in. (I half-thought maybe 'cause I don't drive the stick that often anymore that maybe I'm just expecting it to accelerate nicely at any rpm in any gear, but I can't believe I'm that ignorant of driving a stick just cause I don't drive it that often.)

As starters, yesterday I looked at the bosch platinum plugs I put in 2 yrs ago and they showed signs of running hot. Also looked at the cap/rotor and they didn't look that bad, cleaned off the contacts a wee bit and put it back. I changed the plugs (to NGK) last night, put in another PCV just for kicks. Did not help the problem much (maybe did just a bit). I do have conflicting reports on the plug gap, though. NGK says .044", someone with a good manual (haynes didn't tell me for my engine) said .037 to .043? I gapped them to .044". I will go ahead and change the cap and rotor again anyway. Checked the plug wires at night/dark and no "sparking".

One other thing... I had recently changed the transmission & differential oil; that wouldn't effect any of this would it?

Other causes I'm thinking of...
engine timing off, bad gas, fuel injectors, fuel pump, fuel filter (again?).

Any thoughts would help. Thanks.

[jimmy[the]gent]

its either one of two things. first i would have my muffler and exhaust pipes checkd that could be the problem since cold air goes into your engine. second im leaning towards major engine problems more specifiicaly probably warped pistons and worn cylanders.

[woofhaven]

If the car has a vacuum timing advance, I would suspect that. Probably should check for vacuum leaks system wide as well.