situation: '91 245 LH 2.4, AMM is a 016, ECU is a pink label (gasp!) 561. supposedly 115k on the clock, although i take this number with reservation.

it runs pretty nicely. starts right up in cold weather. idles smoothly right around 750rpm. however, throttle response is slow, and the gas mileage is bad: ~15mpg locally with lots of stops, and ~20 on highways at ~70mph. i don't see any soot or black smoke coming from the exhaust, though.

here's what has already been done that might relate to this issue:
the usual tune up: belts, fluids, plugs, cap, rotor.
o2 sensor
FPR
valve adjustment
kickdown cable
new cat-back

any idea what it might be? i'm planning on checking the vacuum thoroughly and test the engine coolant sensor. maybe clean a ground or two.

oh, at idle i can feel individual bursts from the exhaust tail pipe. can i rule out the cat being plugged?

thanks.