First off I have checked several Honda forums and read many..many pages of problems with VSS, TCU, shift solenoids, TPS and coolant sensors being possible causes.
My daughter has a 92 Accord LX sedan with shifting problems, I will list the problems and the solutions i've tried to get the car going. When we bought the car the speedometer was not working but everything else was fine. Replaced the VSS and noticed it had already been replaced just recently, my replacement also did not fix the speedo problem. She drove the car for a week and started having problems with the tranny not upshifting thru forward gears with only reverse working and D4 light coming on (the D4 light DOES NOT flash, stays on bright or slowly dims and brightens back up and not in a steady fashion). Tried pulling codes through the service plug and no codes come up.
I have removed the shift solenoids, applied 12v's and cleaned them, checked voltage at the terminals that the solenoids plug into and voltage was correct.
Drained and refilled trans fluid.
Including the original TCU, I have tried 3, first one I bought did not work at all, opened it up and had a burned R41 resistor, sent it back and got another, visualy looked fine, put it in and car had same problems as with the original TCU. I replaced all the capacitors in both TCU's, all resistor's ohm'd correctly and this did help some, before capacitor replacement I could only drive the car about a 1/4 mile and would have to pull battery cable to reset it to get home. After capacitor replacement ( in both TCU's) I drove car for 5 miles and only lost D3 and D4.
I have replaced the TPS and adjusted it in different positions, only thing that seemed to help was the idle somewhat, car does have 206,000 miles,
I checked the cable from the throttle body to transmission and it is not sloppy, put very slight pressure on cable and lever at transmission starts to move.
After cleaning the shift solenoids I have noticed that when I put into reverse there is a few seconds of nothing then the sound of like bad syncronizers in a manual transmission then it slams into gear (this only happens shifting into reverse) doesnt do it all the time.
I am at my wits end and keep falling back that maybe one of the shift solenoids are bad or there is a problem somewhere with VSS. I hate buying used parts but the solenoids are $125 ea. my cost, I work at a parts store (CARQUEST) and have for 29 years and have been the automotive field for 33 years.
Any more ideas would be greatly appreciated!!!!