It'll cost more, but I like my 2-1/16" scan gauge from Tone...
http://www.aeroforcetech.com/
The ability to read & clear codes "on the fly" has kept me sane,(or closer to it) more than once.
The larger, rectangular scan gauge is another good option, that is a little le$$ moolah...
http://scangauge.com/
If you're currently using an oiled gauze type air filter, my guess is that your MAF needs to be cleaned, or there's a vac leak in the system.
I recently had a PCV valve split in half, causing a vac leak & CEL with similar symptoms.