I bought this (from this seller) and it works with my Android tablet and Torque application
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=160550105283#ht_3843wt_901
Have I steered you wrong in the past?

Seriously, for under $15.00 this is a blazing bargain. Go for it. You would be more thrilled than the C3 impact wrench which I hammered you on!
By the way, a drop in the rpm of 50 is going to be tough to pinpoint. I am not sure if your vehicle supports faster update speeds. Also I do not know how fast ELM27 can run. Your current scanner should be able to give you pending codes if there are any. You would require a manufacturer specific scanner to get the proprietary misfire count data. Unfortunately, those type scanners are not affordable to us backyard wrenchers.
With the live data, you should be able to verify the correct operation of your TPS, O2 sensor, MAF sensor etc. But don't get your hopes high to find the slight idle problem with the generic scanner.
- Vikas