I had a similar problem with my 1993 Accord 10th Anniversary.
The following were the symptoms.
1. The car would start, with the D4 blinking, and as you start picking up speed, the gear won't shift to 2, at all. So the engine will rev up and road speed still at 1st gear speed. On occassions when this happened, I would turn the engine off, restart and every thing will be like normal and no blinking D4. This happened randomly on 3/4 occassions over a month, and then I started seeing the symptoms of Main relay problem.... like turn the ignition on dead quiet or no 2nd relay click etc. The car would start only in cold and show above symptops after running and being hot.
I pulled the Main Relay resoldered the board, and the D4 blinking problem disappeared since then. I vaguely recall reading some where the D4 blinking being associated with the Main Relau bad solder.
It is not difficult at all to resolder it. Just be sure to get a good magnifying glass so you can check for fine hair line cracks. My suggestion would be to use a solder sucker and take the old solder off and use a new one that way any oxidized old solder won't contaminate the new solder.