A blinking CEL indicates a misfire on one or more cylinders. A steady on CEL indicates something amiss in the emissions system and/or a stored code from a previous event. You should get the car scanned, even if a CEL isn't lit. AutoZone usually will do this for free.
Could have a bad injector, bad spark plug, bad coil, clogged fuel lines, etc. The codes read from the scanner will help identify which cylinder is having issues.