I have similar issue, but mine has the problem ALL THE TIME. No power. Max speed 60 mph.
I ALWAYS have 0mA into the eha, but 8mA is supposed to be the midrange for the early 190's. Midrange is equal to a perfect air fuel mixture, <8mA means the eha is leaning out the mixture I think and > 8mA means the eha is richening your mixture.
In later year 190's, the midrange went to 0mA, then plus and minus from there.
One thing I noticed is that the oxygen sensor input to the computer is shorted to ground on mine. I havent gotten a new computer, but senor output is 0.9V (rich) until I plug the sensor into the computer, then it goes to 0V.! (0.5V is normal oxy sensor output and 0.2V is lean). If you can watch the oxygen senesor output while driving and it correlates the eha output being bad or good, this could be it. (i.e. an intermittent short at the oxy sensor input to the computer.)
I am trying to find a cheap eha valve. I heard they tend to go out on these cars.
Please let me know what you find on this because I probably have the same problem.