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.

Actually, you may be dinged for wearing a suit. I've seen comments, I think some even here on HN, where people have laughed at interviewees that wore suits and rejected applicants because of it.

I'd say "you wouldn't want to work for anyplace that would ding you for a suit". At least I wouldn't.

Well you could have the tie with something else also, like a cardigan. But that works best with a non-silk tie, like knitted wool or something

don't wear short sleeved buttoned shirts, that's a bigger nono than wearing a tie without jacket.

Glad you said it! A jacket with no tie is much more casual than a tie with no jacket.