Hey guys, This morning, I took my car (1997 Mustang GT) to a local Precision Tune for a routine oil change and coolant flush. After they finished, I ran over to Best Buy to get an additional Wii-mote, and it was running just as well as it was before I took it in. After leaving Best Buy, I was headed to get some lunch, and the check engine light popped on. No biggie, I figure, this thing puts that light on all the time. I stop at my lunch destination, pick it up, and get back in my car to head home. As I'm sitting at a stop light, it starts to run a little rough, like it's missing a little bit - you know - burble, burble, burble *cough* (shudder) burble, burble, burble *cough* (shudder), etc. Anyway, I get it back to my garage at home, and popped the hood to check for anything looking out of the ordinary and for any leaks. Everything looks great, one weird thing I did notice was when I shone a flashlight under the intake manifold, there was a hold in the top of the block, like a plug was missing or something. I've never really looked too closely under there, so I don't know if that's what it's supposed to look like or not, though I doubt it. So, I let the car cool off for a few hours, and then head back out there. I notice the coolant level is low, so I mix up some and fill it back to full. Also checked the oil level and it seems fine, as did the gauges in the car when it was running. I crank the heater up and let the car idle for 5-10 minutes and it seems fine, burbling away happily, idling in my garage. I decide the time has come for another road test. I back out of my driveway and it seems normal, and then accelerate down my street, and feel the obvious lack of power. I turn right onto a bigger street and try to accelerate, and it's getting worse... to top it off, now the check engine light is flashing at me and the car is shaking a bit harder. Assuming this is bad news (a Google search when I got home confirmed this thought), I immediately turned down a side street and limped her back home. About halfway home, the flashing stopped, but the light remained on. It still drove roughly, and when I pulled it back in my driveway and hopped out, I thought I smelled a faint sulfur odor, which made me immediately think of the cats. I don't know what's wrong with it, but the behavior and slight odor are making me think it's emissions system related. Exhaust system is all stock, car is mostly stock now aside from a Densecharger, tune and few other minor things. Do you guys think anything the shop did today could've had an impact on what I'm experiencing now? Is it just a coincidence? Could that hole on top of the block have anything to do with it, maybe they forgot to put a plug back in after draining the coolant? Sorry for the long post.