Ok I have a 88 tii with a not so good engine and rather than rebuild I'll just wanna put another engine in it. I'm looking to get a S5 engine to put instead since they are better. What would I need to get. Just the ECU and wire harness, that all? Or is the ECU compatible? TIA.

 

If you use all of your sensors you can use your ECU. The main party is swapping the front covers so that you can use the 88 front cover. You'll need that so you can use the mechanical oil metering pump.