Ideas on partial throttle hesitation?

[LateFan]

Ideas on where I should look next? -

Nice smooth idle at 650-700 warm or cold. (needs to warm up for a while when cold)
Good acceleration (for an e) at open throttle.
BUT >>> Some hesitation / stumble at very low partial throttle. Open it up and it goes.

'86 es auto
170k mi
New ICV, all hoses & gaskets, temp sensors, 02, fuel pressure regulator, fuel pump, injectors rebuilt, MAF rebuilt, rotor/cap/plugs, valves adjusted.

Just feels like the mixture isn't right on partial accel. Mileage also isn't in the high 20s where I'm hearing an e should be.

Thanks -

[EatsHondas]

My money is on vacuum leaks. You can make your own rig on the cheap to find them. Basically you'll remove the AFM, plug the exhaust, and pump the system full of smoke. You will almost certainly see small wafts of smoke coming from spots around the engine.

A hesitation with the stock ECU almost always means you're too lean. The car takes off at WOT because the ECU ignores data from the AFM and runs off a preset fuel and timing curve. If you partial it with vacuum leaks, the car will misbehave because the engine is breathing air that has not been seen by the AFM.

[LateFan]

It's had a series of smoke tests, from our home-made one to a shop saying there were no leaks. That doesn't mean none have developed since. I'm suspicious of the dipstick o-rings for one thing.

When I drove it, it seemed to be in the off-idle 800 to 1500 rpm range. Then I noticed a slight surging/pulsing under load at a steady 2000 rpm, climbing a hill.

[EatsHondas]

Have you tested the throttle position switch? If it's not working properly, the ECU might not be able to tell the difference between no throttle and a little throttle. A bad or going-bad crank position sensor can also cause intermittent issues. There are easy multimeter tests for both of these components.

[LateFan]

Yes - should be good, unless they can slip.

CPS is new. Also new o2 sensor, then we pulled it out and tested it with a multimeter and a torch. Looks good.