Offroad-Express

Hey guys.
Car: 1991 Escudo G16B 16v
Resent maintenance: Headgasket, timing belt, oil change (all done by previous owner) , spark plugs, one spark plug lead and coolant change.

Bought the escudo a few months back and everything was fine until I had a problem with high idle.
Took the throttle body off and cleaned the IAC which helped for a bit but now its back with bigger problems.
The idle is high for a few seconds when cold then slowly drops to around 1000rpm at which it starts to misfire and run rough. When i take the thing for a drive it hesitates quite badly but not in first and sometimes second. I will put my foot on the gas and nothing will happen or it will jerk slightly then all of a sudden get power and rev up.
I've also cleaned the egr valve to no avail and checked the timing which was spot on.
Quite alot of steam comes from the exhaust on cold mornings but seems to go away when warm. (hoping its not a cracked head...)
Also noticed a large crack in the exhaust manifold (above the o2 sensor) hence my other thread.
Could this be my problem? o2 sensor getting wrong readings?
Going to do a leak down test on the engine next week.

Any help is much appreciated.
Cheers

So i took the distributor cap of today (should have been one of the first things i did) and found the points covered in white powder, corrosion? and some small cracks coming from two of the points. Ordered a new new so fingers crossed.

The white stuff is supposedly not too much of an issue but the cracks could be bad. Defiantly do the leak down test to make sure the head is not cracked then I would replace the exhaust manifold as this supposedly effects the oxygen sensor and fuel mixture at idle. Failing that do the rest of the plugs and leads and check the cam timing is correct.

Did a compression test (could get hold of the leak down gear) all cylinders between 195 and 205 so not bad. Decided to throw in the leads from my civic just to count that out and boom! she is running like a dream. Still going to do the distributor cap and rotor but glad its running well again.