Surging and loss of acceleration on '92 Metro

My '92 Metro 5-speed 3cyl has 205,000 km and has been a real trooper for my daily highway driving for work. Yesterday, I was going about 90km/h down the highway when I experienced some surging and lack of acceleration. There was no power loss and the engine kept running, but I was unable to keep up that speed. I ended up getting home by going no more that about 70 km/h. There's no sense of problems through 3rd and 4th gear up until around 60 km/h. I pulled into a mechanic that I use and he pulled the distributor cap off. He said he could tell right away that's what it was. He replaced the cap and rotor and sent me on my way. No problems after that. No problems on the 1 1/2 hour commute to work at speeds up to 110 km/h. Then on the way home, had the same surging and lack of acceleration at higher speeds (this time around 80-90 km/h). 6 months ago, I put in platinum spark plugs to help with a Hydrocarbon problem for aircare testing. Compression testing at that time showed the 3rd cylinder quite low. Could this be anything to do with the compression? My mechanic said we can check the leads. Some other posts lead me to think that it might be a TPS issue?
Car runs fine at speeds up to 60 or 70km/h.

Any comments would be appreciated.

Your symptoms mirror exactly what happened to me. :sly:

After the motor quit completely and I had it towed home :disappoin it ended up needing a new motor. :2cents: :banghead:

I'd go back to reguar plugs. Never had any luck with platinum unless they were called for by the manfacturer. :grinno:

Check for burnt valves..My brother had the same problem with his Metro and come to find out it was the valves..