I have a soon-to-be-classic Peugeot 205 GTI, a 1986 C-reg that I've owned for 18 years. It's done 120,000 miles and is in generally good shape, but has an annoying problem of pinking and misfiring. It starts fine and the trouble never shows up when the engine is cold, or when ticking over or revving stationary, but only when the engine is warm and the car is under load. It becomes very unpredictable - sometimes accelerating away from a roundabout has the thing stuttering so much I think it might stall, but usually the problem can be cured by flooring it. Then, when lifting off or going back on the gas, it sometimes backfires. The sparks plugs look fine, the fuel filter is recently new and the fuel pump is a bit noisy but otherwise OK. Things seem to improve after a light spray of WD40, but it's not perfect. Could it be something as simple as needing a new distributor cap, or maybe more serious?