Like many of you i fell in love with the rx8's iconic engine noise and saw a mint rx8 for sale with a blown engine.

One half assed rebuild later with a doner engine and I'm having some issues.

Exhaust also not attached.

Sometimes she dies when getting up to temp, but she'll idle around 750-850 rpm

Replaced:
- Spark plugs
- Coils
- Starter

Does anyone have suggestions for things to replace?

 

Are you revving or is the car revving itself?
The ECU needs to learn to idle after a battery disconnect, and it may die while doing so, especially on an unknown rebuild.

What exactly was half-assed about the rebuild? I mean.. that seems like the obvious problem here.

Any mods? Any OBD codes?

 

Revving it myself, on idle it stays around 750-850 and revs to 1200 every once in a while.

Main relevant obd is saying it's running rich.
no mods 100% stock

Once it's hot it'll idle for 30 minutes no problem

 

First guess: injector plugs mixed up or ignition wires mixed up. Easy mistakes to make when reinstalling an engine. If you have the rest of the OBD codes, there might be clues.

 

When you said plugs mixed up, my first thought was the timing could be off. so i ordered a 2nd new crankshaft position sensor and she's been running better than ever.
Thank you for the pointers. We'll see if it keeps running better with breaking in

 

Great. You probably also want to do the 20-brake-step memory reset. Among the things it resets is the ESS position sensor calibration, which is not reset by pulling the battery. Possible your new sensor is a better match so the original calibration than the 1st replacement.

 

Glad to hear the new crankshaft sensor helped! I'd definitely second what Loki said about the 20-brake-step reset. It helped my rx8 run smoother after some work, though I'm not 100% sure why.