I returned from Iran 3 weeks ago.
Diesel still 165 IRR wirh card, but no problem for us. You must visit petrol station with truck and ask truck driver for help. Really everyone will help you.
Diesel near the Armenian, Azerbajan border can cost 2 or 3 time 165 (owners of petrol stations make privat bussiness).
The cheapest diesel in Turkey I bought for about 2,3 ITL sometimes 2,5 ITL, normally 2,7 - 3,00 ITL.