Car shuddering and almost no power?

[Plummer]

It's ALWAYS after or when it's raining and the car has been sitting.

It's like erratic idling, and when I try to accelerate there is no power, to the point where it's dangerous when trying to pull away and the car feels like it wants to cut out.
The harder I accelerate the worse it gets, sometimes to the point of the engine light coming on.

I have in my mind that the exhaust is leaking badly, and water might be getting in and causing a pressure block from the engine.
Seem viable?

Thanks!

 

[Plummer]

No one?

 

[Ged]

not water on the HT leads?

 

[Sam@NP]

I had a similar issue, changed the MAP sensor and HT leads been fine since.