With older Volvo cars, like 200s, 700s in the '80s especially when fuel was more problematic and with high mileage engines (well over 100K), the backside of the intake valves built up alot of carbon and it ONLY effected cold starting (nothing else).

The engine typically starts and stalls, then starts and runs fine once the carbon deposits became saturated with gas. The carbon buildup acts as a sponge and absorbs the initial dose of fuel when the engine is first started cold and that's why it stalls.

The cure was to remove the intake manifold, rotate the engine so that the intake valve was closed and blast walnut shells against the valve until all the carbon is removed. It works great too, better than any chemicals.

This isn't a cure for "sticky" valves (hydraulic lifters) like on 850s for example.

Our shop still has a walnut shell blaster but I havent seen many older cars (200s, 700s)with that condition in years now because gas is better, more additives.