I have a 1988 NA ‘vert that has some starting problems. It blows a cloud of blue smoke on the first cold start, and starts *very* rough (see video). If I start in-gear, it barely idles up to 1500rpm, and if I start it in neutral it only gets up to about 2000rpm for a few seconds before dropping down to 1500rpm. Until a couple weeks ago it would start fine, in or out of gear, idling to 3000 in neutral and up to 2500 in gear before dropping down to 1500.

In the second video, you can see/hear it sounding like it’s missing here and there (right after the cold start).

After it warms up it runs perfectly, no smoke, no hesitation/missing, no loss of power, but while it’s cold it is not happy. Current ambient temperature (when this video was taken) is 14°C/57°F. It hot starts repeatedly just fine, but the longer it sits the more rough the start is. It only started doing this about a week and a half ago, right after I changed the oil and took a long (1100km) road trip. New oil is 5w40 full synthetic, old was 10w30 full synthetic.

Maybe it doesn’t like the new oil, and maybe there’s oil weeping past seals and accumulating in the combustion chambers (maybe through the OMP)? There’s no gas dilution in the oil (from what I can tell), and I’m 99% sure the OMP is working since the oil level has been dropping at a steady rate since the last change. Or somehow the cold start assists have suddenly failed (but that doesn’t explain the cloud of blue smoke)? Any thoughts/diagnostic advice would be very much appreciated! I’m going to be putting it away for the winter soon and I’d ideally like to get this figured out soon.

Video 1 (Cold start in neutral, exhaust view)
Video 2 (Cold rev from idle to 2000, audible intermittent missing)