when it rains and i go over puddles, the engine starts to rev up and down and wont accellerate,?

i have a 95 318is and i have a problem when it rains and i go over puddles, the engine starts to rev up and down and wont accellerate, after a while it starts idling well again..it happens when it rains and sometimes when i start the car, then it corrects itself . What could this be , please help

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[Nick at Pelican Parts]

Check the passenger side of the engine compartment by the firewall and see if you're getting water into your DME computer which is mounted in the firewall.

- Nick