1996 Celica St204R Low/rough Idle

[ZRENO]

Hello all, I ask in advance that you forgive my possible ignorance and lacking knowledge in engines and cars in general.

I recently bought a 1996 Celica ST204R manual. (I think that makes it the 'SX' trim? Engine is the 5S-FE.) and have been driving it without issue for the past few weeks.

Yesterday was the first day I went without driving it since I bought it. When I started the car today it would only idle around 500RPM, making the whole car shudder with a decent amount of white/grey smoke from the exhaust along with a chugging sound. The rough idle settled to about 1000RPM after about two minutes of driving, and the smoke eventually went away only after winding the car out to 6000RPM a few times along a country backroad.

When driving the car normally, I sit at around 2000 - 2800 RPM which is usually 3rd or 4th gear depending on the road - the same as I did with my previous car (92 Honda Prelude). Does the Celica need more revs to run efficiently and not clog the engine than other cars? Or is this kind of rough idle regular behavior for this car? I run the car on RON 95 petrol.

Thanks for your help.

EDIT: Turns out it's a blown head gasket. Brilliant.

Upon further investigation, other symptoms included 'chocolate milk' radiator fluid and engine overheating due to lack of circulating radiator fluid.