Ok, here is what I found. The one on the right is from a 96 (which is when they supposedly changed the TPS, but I know that particular one is the same as the pre-96 16V TPS). The one on the left may be the one you are looking for...I can't remember what it came off of. Ok, I just remembered I had a 97 16V motor here and I looked at it and the TPS is the same as the one on the left in my pics. So I am guessing it is the same as your 98.
They both take the same plug. They both have 4 pins. All 16V TPS's that I have ever seen have all had 4 pins in them....not sure what TPS you have seen that only has 3...even the 8V TPS's have 4 pins.
Let me know if either of these look like the one you need.