HELP!! 2004 AT RX8 Dies At idle
 

Ok, so I brough my rx8 as a project car. I put the engine and tranny in myself. Had to de-flood the engine as soon as everything was in. After car start and after further e-val I found out that it had a bad cat, so I switched to a catless exhaust. Also, I swapped to a 3inch cold air intake. In addition, to trying to get the car running correctly, I swapped the coils to corvette coils. Ive upgraded the started, new radiator, mishimoto fan shroud, and added a 3000watt sound system to the car. I've changed the MAF already as well. I have only driven the car about 200 miles for diagnosis purposes. I got the engine with 68k miles from JDM with a compression video which showed 90psi (i think). So......I've listed all the upgrades thus far. NOW, my issue is that when the car has been running for a while it dies at idle but once it dies it starts right back up instantly but I have to keep it in neutral with my foot on the gas in order for the car to stay on at a stop. Can someone help me?

Compression for rotary's is measured in bar. If your engine tested at 90psi, that's only about 6.2, which isn't good. Plus you should've had three sets of numbers for each rotor.

Does it only die after its reached normal operating temperature or does it die at a certain rpm? Have you checked for vacuum leaks?

Go back to the stock intake. Some intakes make everything worse and no intakes maky anything better on this car. You having to keep your foot on the gas makes me think this is at least part of the problem.

If it starts right back there is still hope, but 90psi could be a dead engine. Depends on the rpm at which it makes that 90psi.

Play with it today and now its hesitating to pick up speed and dies when foot is on the gas pedal.

But it has no power loss. Could it still be dead?

Yes. You can't feel a power loss of 20-30hp, especially if you're not used to the car. Do you have thr actual compression test video? Can you figure out from that what rpm it was turning at? Precise time between peaks on the meter and a bit of math should give you that. 90psi at 200rpm is borderline, 90psi at 250 is failing.

​But verify the other things recommended above, if it restarts easily after dying, there is still quite a bit of hope.

Put the stock airbox back in ASAP. All but 2 aftermarket intakes rob power and cause poor idle. Those 2 (AEM and Racing Beat) work OK, if you follow the installation instructions exactly to the letter, but they add nothing but noise to the equation. The stock airbox is the best intake for this car.

Ok, gonna do some test this weekend an will report it all, even a compression test.

Keep us posted on the results of the compression test, even if you are just using a piston engine compression tester with the valve removed.

I had a Similar problem at idle with 05 MT. the problem was I had air trap into the coolant system. what I did was turn the car on ( if car is cold remove the coolant cap off ) when engineer start to get hot the air trapped into the coolant system will start to bubble out ( grab a new coolant bottle because you gonna lose some of that was inside when you see that the coolant went down poor little bit till you fill the tank ( d'not overflow ) take your time and doing it till you see the idle going back to normal. you need to bleed all the air trap out of the system.

Mine also was dying at idle, this had started after changing the battery. After letting it just idle for 20 minutes the computer got happy and all was good...

04 rx8... same problem
 

Went on a 3 month patrol and the car was parked at the house. Wife drove it once while i was gone and reported no issues. I got home, took it out for a drive and experienced no issues. The next morning i got in started it up, warmed the engine and proceeded to the base. About 10 minutes into my commute while at a toll plaza and in nuetral, it died. Had to get pushed out of the lane. Let it sit for about 35 minutes, started up and continued my commute. Car stalled again when I was attempting to reverse back into a space. Long story short, left later that evening, got about 5 minutes and it died again. Towed it to the shop. Since then they relplaced plugs, ignition coils, oil, element, starter motor, solenoid valves, and throttle body. The Japanese mechanic seems to be throwing parts at this problem with no proper trouble shooting. Any idea? Engine done, poor compression somewhere? I have read several threads in this forum with similiar issues but have not seen anyone come back and say "this is what caused the problem". Thanks in advance for your responses if any...

Sounds like you need a compression test. The mechanic has already changed everything else that couls be responsible.

Well there could also be the fuel pump.

An easy way to test is to see if your car has problem going up a hill or when you floor it. If it does then you should further check the fuel pump, if it doesn't then you should check the engine compression.