[Jamesp]

Spongy brakes *could* mean that the clutch slave cylinder (which is part of the brake hydraulic circuit) is spraying hydraulic fluid onto the clutch / flywheel assembly. This is a bit of a stretch, but entirely possible with the sudden onset of smoking. If the engine was running normally, and the smoke was coming out of the side vents (not any out of the exhaust!), then starting would be ok, but not the course I would choose first. The only data I could imagine by starting that would be gained is a coolant leak and steam. If you smell burnt, and not sweet (like maple syrup) then a coolant leak is out. Look under the car where the engine and transaxle meet (just in front of the bell housing by the back of the engine) is there a drip of fluid there? If so soak it up with a paper towel. What color is it?, clearish with a few black specks would indicate brake fluid. Uniform dark brown or black is engine oil. I'm not sure how good your nose is, but if you know the difference in smell between brake fluid and engine oil that's a dead giveaway also. So I'd start by 1) smelling the smoke - does it smell burnt or sweet? if burnt then it's likely the clutch, 2) is it leaking fluid? if so then what is the fluid, brake fluid or oil? In general, the jumping RPMs indicate you are in for a clutch job due to wear or contamination. A coolant leak would not result in increased RPM without a corresponding increase in speed. If the transmission were shot I'd expect lots of sound followed by no forward motion at all.