I have an 05 manual RX8. I recently replaced the engine due to busted seals. When I start the car, it seems to run fine. After driving it for a little bit, if I press the clutch in and let the RPMs drop, the car dies. It happens when I come to a stop and hold the clutch or put it in neutral. I can keep the car running, as long as I gas it enough to keep the RPMs from hitting 0.

Sometimes I will get a delay in response time of me pressing the gas, when coming from a stop. Other times, the car will act as if the engine has died (I get the dash lights and all) but, if I try to start the car, I get the grind when you start a started car and then it feels as if the car started back up again. Most of the time, it dies completely and I have to start it it over again.

At first it would take a while before it would take effect, but now it's after driving couple blocks.

On occasions the car will not die, but the car will sputter, and the RPMs will fluctuate between ~100 and ~2K RPM.

At first, there was no check engine light, but now I am getting the codes P0301 and P0031, which are Cylinder 1 Misfire and 02 Sensor problem.

I am in the process of replacing my catalytic converter, as I've read around and found similar, but not exactly the same problems I have, but it's due to a clogged/busted CC.

I was just wanting to get opinions from others to see what else I should look into as a possible cause, in case I am overlooking something or not looking in the right place.

 

I had the same symptoms the last time I had my engine replaced. It was due to low compression. Performing the SeaFoam/ZoomZoom Cleaner treatment on the engine might help. It can't hurt. Check the DIY section for instructions.

 

Bad idle can sometimes be an air leak somewhere past the air mass meter. Check all vaccuum lines, pvc, etc.

Sounds like a new O2 Sensor would not hurt either.

Hopefully you did new plugs, wire and coils when you replaced your engine.

 

Thanks for input, I will look into the seafoam/zoom zoom cleaning. See what I can find.

And yes, replaced plugs/wires/coils. I've already replaced the O2 sensor once, about a week after the change, and the new one marks bad after another week. I am replacing both sensors with the cat, just to make sure.

I had the air leak checked once, but I don't think it could hurt to go over it once more, but to follow up. The idle doesn't get bad, till after the car has been running a bit. After the car has been sitting for a few hours and I start it up, it runs great. It's just after riding a few blocks, and I come to a stop, I get bad idle. Assuming the car didn't shut off.

 

Make sure the nipples on the aluminum part of the intake manifold (on the passenger side of the engine) are either capped (which I think is the case on 04/05s) or connected to the PVC vent lines. A vacuum leak there will raise havoc with all kinds of stuff.

 

I have an 05 Manual, she ran beautifully before. Got flooded, had the dealer deflood her and now she has this issue. Did the cleaner work? I'd appreciate the input. Thank you.

 

I know this is an ancient post, but having this weird issue..
I also noticed some lights dimming/loss of power as I hold the clutch in (more apparent at night)

I have an 04 Sport that had been sitting, just replaced the fluids/oil and the SSV solenoid and don't have any CEL currently (my coolant fill light is on but that's broken like everyone.)
I reset ecu with 20 brakes, the car will start a little rough but then idle fine.. until i press the clutch..

Thinking its a ground issue, or potentially clutch switch or neutral switch...
Maybe pertinent- it has the issue at the top of the clutch activation, just pressing it a little it will start to die.. I can rev it up with the clutch pressed and it will live until trying to idle.

Will check switches tomorrow and report back.. ( via: https://www.rx8club.com/series-i-do-...switch-200453/ )

 

Well.. Got my multimeter ready and my wire brush and everything.. Went under to find it just ripped off/mangled/melted/who knows..So who knows when my neutral switch broke.. but no need for testing....


But yeah, IDK how I researched enough to make me think this was a neutral switch.. I think i saw people reporting car dieing when they released the clutch (mine was oppposite) I never got a CEL for this switch!

 

 

here is the fixes going in. Storms were closing in so I didn’t document the rest but I connected these and wrapped it all up in electrical tape, then zip tied the new slack to the wire harness.

car is running awesome, idles strong and smooth. Happy I got it sorted out. Thankfully didn’t really have to buy anything. The switches are pretty dumb and bullet proof but these wires and connectors are a super common issue so hopefully this helps someone figure theirs out.. 🤙🏼

 

Ahh funny issue. A similar issue is with the Manual reverse transmission switch. If there is a short or an issue it will blow the 15a ignition fuse.

It gets kinda comical when you pull into a space fine, but kills the car going into reverse..... did mazda have to put it on such a main fuse?.....Probably some safety yahoo that required it for the reverse lights.

 

I actually went to strip the insulation back on the neutral sensor wires and one of the reverse sensor wires (white) basically fell off. So I actually repaired 3 connectors (pictured)

So yeah these things are a total weak link.. Just glad I had enough room to wire in some new stuff and it didn't break right at the sensor..

 

Just swapped same engine into my rx8. Replaced most common parts and yet idle will fluctuate between 1.5k and 2k rpms then after a couple mins dies. Any help or ideas will be highly appreciated.

 

Miswired ignition, miswired injectors. Easy mistake to make when installing an engine.
If not that, check for vacuum leaks. This is kinda common, there should be other threads with similar issues.