2006 Scion tC with 126k miles. Automatic and no engine codes. It's been stuttering when I let it idle, its not constant and somewhat random. You can feel the engine stutter for a half a second, and you can hear it too from the tone of the exhaust. Rpms drop by about 100-200 when it happens too. Tried to diagnose it myself, looked for a vacuum leak, tested MAF sensor, evap purge and still no dice. At first I thought maybe spark plugs or coils, but my BlueDriver shows no misfires. I didn't want to spend to much time with it so I decided to take it to a mechanic. When I took it too him I explained the stuttering issue, and that it now had one code for the MAF sensor because I left it unplugged while diagnosing it and that it wasn't the problem. Sure enough two days later I get the call saying the MAF sensor was indeed the problem. 400 dollars later I pick it up and what do you know nothing has changed at all. Then the dude is like oh it was running poorly before and he told me to drive it for a few days and the problem would clear up. I argued with him saying no you didn't fix anything, then left it with him. Well that's where I am at now, I am sure he doesn't know what's wrong with it so I am just gonna ask for my money back and try to fix it myself again. Anyone have any ideas on where to start? I might replace the sparks and coils anyway just to be sure.