I'm assuming all scanners will check sensor voltages, fuel trims, etc. Granted, the one the guy used on my car was an extremely nice one, I'd be willing to bet they all have a diagnostics test they run on the car (how to run it, I'm not sure). If this doesn't result in any errors, try looking at things like TPS percentage. For example, if the TPS is supposed to read 1.00% while at idle, but reads 0.88% (like mine did) you may have located the culprit. Even though mine idles fine, in actuality it may need to idle slightly higher (currently idles around 750). Just the 0.12% it's off could keep the idle 83 RPMs lower than it should be.
Not claiming to be an expert here, but any info I pick up I'm more than willing to pass along
