rust in the dme?
 

I took out my dme to put a preformance chip in but when I pulled it apart I saw what looked like rust all over the circut board. I went to wipe it off but it turns out that what looks like a clear coat of some kind is flaking off and it is a dark rust color. I know that this cant be good but is it somthing that could be causing my car to run less that great. I have a idle issue but not bad and also the car surges a bit when driving at a constant speed. I found a few dme's on ebay for a few hundred dollors but how do I know if they are funtioning rite. Is this a common problem with the dme's or what. By the way, It is a 86 na 944. I love my car and want it to run good so sorry if I ask to many questions. Thanks for any help in advance.
brad

Is there rust or any discoloration on the metal case at all? 85.5+ are notorious for having leaking battery trays, which lets water drip right onto your DME which will cause what you are describing.