I've got a 2007 RX8 with 40k miles.

I started having issues a month or two ago. First, the car was slow to start (took a few seconds of cranking for it to turn over). Next, I noticed that I had a lack of acceleration (particularly at low RPMs). Finally, a couple days ago the car started idling a little rough.

I noticed that my gas mileage on the last couple tanks has gone down as well.


I still have a few months left on the engine warranty, but I'm a little worried about taking the car to the dealership right now. I've regularly checked/changed the oil, but I'm sketchy on the other suggested maintenance. If it turns out that the engine is losing compression, will I be denied warranty coverage if they find (for example), that the spark plugs weren't replaced? Anything else I should check before taking it in?

 

Well every one of those symptoms you just named pretty much points to low compression(speaking from my personal experience). Those could also point towards ur plugs/wires/coils which should all be replaced every 30k miles. But if I were you, some dealerships will require your plugs/coils to be updated before a compression test, if you havnt replaced them, you should do so anyways. But as long as your under warranty, and you prove you changed your oil you should be fine. They might want you to replace the plugs, but as for getting the engine, you should be fine.

 

Here is a list of things to go thru to check for yourself if you want to troubleshoot before taking it in.

https://www.rx8club.com/series-i-tro...t-here-222584/

 

All your symptoms point towards weak ignition.

Replace your coils, plugs, and wires
Clean your air filter box and replace filter,
Clean MAF Sensor, Throttle body,
Clean ESS, Reset ECU

when you start the car for the first time, let it idle for 10 minutes to re-learn the fuel trims

Report your findings, and then get a compression test for your peace of mind :-)