I have a 1994 Honda Accord, 4 Cyl VTEC Auto trans, 210,000 miles. Today was
the first time this happened, but I just bought the car last weekend.
Replaced plugs, wires, and checked the Trans fluid. The D4 light is flashing
an 18 code. It doesn’t do it all the time, but today when I started it up to
go home from work, I put the car in gear and noticed reduced power; I then
noticed the D4 light flashing. I pulled over after a few miles and turned the
car off and when I restarted the D4 light was not flashing anymore and the
car ran fine. The speedometer works intermittenly also.

I have also had two instances where the car would not start back up right
after turning it off. It just turned over. After waiting a few minuets the
car started right up. I don't think the two instances are related, just
thought I would throw it out there.