sounds like a vac leak. with the intake off, put your hand over the TB. if the motor continues to run, you have a leak somewhere. the pulsing is usually the iacv compensating for a leak somewhere. could be something else too but this is the most common problem. check all vac lines and check your intake manifold nuts.

 

last time that happen to me it was a coolant hose leak. Dont ask me why but that was the problem. at first it wasn't a noticable leak but a mile or so down the road it became a bad one. ever since i fixed it, it never cam back. maybe chech all your hoses.

 

every single honda i have ever owned in my life... never had an iacv go bad... but every single one of the hondas i have had... had this problem you speak of..... every time... it was the tps.... to find out if it is the tps.... while your car is off... unplug it (its on the back of the throttlebody) then start your car... the up and down idle should stop... if not... then your werent as lucky as me...lol