2001 150 HPDI throttle plates sticking

I have twin 2001 HPDI 150's. The starboard engine was idling high. I took the backfire arrestors off and found the throttle plates corroded/rusted, and sticking. I cleaned them, and they worked fine for two weeks. After sitting a few weeks, the problem returned. i cleaned them again. After a few weeks of sitting, I went to use the boat and I could get no throttle response from that engine. I found that the corrosion had returned, and was causing the linkage to stick. There are only two of the six plates causing it, the rest are fine. Can the intake/throttle plates be serviced, or am I looking at replacing the intake & throttle plates?

Any help appreciated

[robert graham]

those plates should be made of brass...is it metal corrosion or a carbon build-up like on an automobile throttle body. carbon fairly easy to remove with carb cleaner and a tooth brush, but don't know what would cause a brass plate to corrode like that unless some salt water is getting in to it?

Actually the throttle plates are stainless steel. Not true stainless, as a magnet will stick to them... and they rust.

I was wondering if anyone had ever drilled the rivets out and pulled the bearing rods in order to get them freed (the rods), so that they will roll freely.