I remember the situation was already dire by 1985 due rampaging corruption, lack of worker`s motivation and resulting shortage of goods. Realistically, you should expect most of history tweaks will shorten Era of Stagnation (Era of Decay), not make it longer.
I should highlight the lack of motivation. Actually working persons percentage in 1985 was well below 10% everywhere, and may be as low as 2% in select industries.
Actually problem was partially understood in time - in 1984 the anti-alcohol laws and police ambushing people on street in the work time was tried to create more motivation to work. Because most visible phenomenon was of workers absent on the workplace, lining up in the queues before vodka-selling shops. It did not help much though.