Ii have a 2004 rx8 I bought it 8 months ago it had 500 miles on the rebuild, everything under the hood is new, cat is new now it has 5000 miles on it and won't idle when it warms up..I replaced spark plugs, reset ECU, put a optima battery n it fuel pump is new also, it had 3 compression tests 1 after rebuild 1 at 500miles and another at 1500 by Mazda... compression was good..it has had a hot start issue that was on I drive 20 miles to work so it has all day or night to cool off...I've looked at other posts and everyone seems kinda hung up on compression..I won't rule it out, can we first look at something else and if all else fails then concider compression...if everything is what could go wrong within 5000 miles? Also get oil changed every 2000 miles follow directions as close as possible for break in...and drive it like I stole it after that..coolant light is on and Mazda checked it out and did it was nothing to worry about as it doesn't leak at all...only other thing is after market o2 sensor at cat shorted out so its unplugged but all these things were there at 500 miles and it's been fine