Don't know why this is being downvoted. It may not matter much in engineering circles, but anyone who is knows how to dress knows that a tie without a jacket looks silly (or like you just came from a high school homecoming dance.)

Let the downvotes rain you jacket-less tie wearers.

On topic: OP, you're never going to be dinged for wearing a suit to an interview. You may be taking a chance by dressing down. How people perceive you at first glance does matter, whether we like it or not.

Personally, I would wear the suit. That said, I have been involved in more than a few interviews/hiring decisions, and I've never rested my decision on dress (if you showed up in shorts and a T-shirt there may be an issue as it says something about your attitude.) I wouldn't give a leg up to the candidate who wore a suit over the candidate who wore a button up and chinos, but that's me, and we all know that dress isn't exactly something which is on the mind of many engineers.