I had an 80 a few years ago, mine was a 1.8 S, I don't know if it helps but I had a similar fault with mine, except mine wouldn't idle very well either, I found a vacuum hose to the inlet manifold had a split in it so it collapsed when under load. Taping it up didn't work because the little bugger imploded under vacuum. Replacement was easy once I found one.
Euro Car Parts UK - European Car Parts were very handy! Hope this helps. Now, can anyone sort my 2.6 V6 coupe please?