Why are your grades dropping? If they are because you are not motivated to study specific computer engineering-related courses then maybe it is a good idea to change majors. If it is because you are having a hard time with basic general engineering courses, such as Calculus or Physics, then switching to IE is not an option, since IE has the same basic coursework as all engineering areas.
To be able to do well in IE you need to like math, statistics and logic reasoning, and also like to plan or project things.
Go to the IIE web site (iienet.org) and browse the IE magazine and try to make a decision based on the type of applications you see there: OR, simulation, human factors, decision analysis, etc.