Not sure if it's the same issue or not but I had a V6 Telstar which had something similar, especially when the weather was warmer. The problem turned out to be a crack in the silicone coating on the circuit board inside the
distributor. From memory upon removing the
distributor cap there were a couple of screws to remove which enabled you to flip the circuit board over to view it. This was a common problem apparently with the V6, over time the silicone coating on the circuit board would harden with the heat and develop cracks. This then allowed moisture to build up (especially under warmer conditions) and the moisture would eventually get into the cracks and start to corrode the circuit board and cause it to short out. I tried everything from replacing coils, leads and spark plugs but all to no avail :( It was just by chance that I happened to take into a mechanic mate of the brother in laws to have a new clutch fitted and when I quizzed him about the problem he said he had come across it a couple of times and had replaced the distributors with refurbished units and the problem was solved
Might be worth looking into at least to see if your
distributor is the same setup
Cheers