'83 GLW. Hitachi, Calif model:

 

This has become more pronounced over the last couple of months. While cruising at part-throttle usually in 2nd or 3rd gear in the 2500-3000 RPM range (just going the speed limit kind of driving) the car kind of "bucks" until I let off the gas, or aggressively accelerate. No sputtering or backfiring, just enough buck to make passengers' heads look like "Bobble-heads".

 

I thought it might be starving for air, removing the air filter lid had no effect. The O2 is last-year new, cat original. New muffler, new plugs, rotor, cap, Magnecor wires.

 

Since this has gotten really bad, the gas mileage has gone from the high 20's(25-29 MPG) to around 22. The engine starts and idles idles beautifully, even on sub-freezing days.

 

My guess is carb, but any other ideas are certainly welcome.

I would check these things to try and find the problem.

 

The fuel pump may be weak so check the fuel pressure. Check the intake system for a vacuum leak. I have had to replace the intake manifold gaskets before. Your CAT may be causing some back pressure in the exhaust system.

 

PS- Say hello to the Cartwrights.