Long Fuel Trim?
 

So, first of all...hey guys!
I have an 05 RX8 that is used and Salvaged Title that i recently bought. Of course, there are problems with it and i have no idea as what to do. Taking it to a mechanic here and there and recently the guy ran the ECU and it reported a 23% long fuel trim and he says it should be around 4%. He said i need a new front O2 sensor to fix that problem (so i believe). I bought the part but i am going to install it myself.
What i wanted to ask is what is wrong with a long fuel trim with my current %? Mechanically and performance wise? Because i feel that my 8 is too slow for 240hp.

Another question, how do i remove my speedometer? Need to put a light bulb for my check engine light.

Thanks in advance.

The ECU is good enough that the long term fuel trims will typically stay within +5% to -5% if everything is working correctly. Positive short term fuel trim with a low MAF g/s is an indication of a vacuum leak. In theory, if the car was driven long enough like this the long term trim would learn those positive short term trims.

Just reset the trims and be prepared for that to uncover something fairly major somewhere, probably a vacuum leak.

Take a look at the New Owners thread at the top of this subforum and in my signature below. There is a "what to do first" list at the top of post #9. You should very very very seriously address those points.