Fluctuating RPM at Idle and Stalling
 

My 05 RX-8 is fluctuating between 750 and 1000 RPM every few seconds when idle. When it hits the low end of 750, the car vibrates a lot. I'm also experiencing problems with the car picking up speed when it happens. I can floor the gas pedal and it still takes a while to get going.

A video of the issue:

When it happens:
- When in drive at idle
- When the engine is HOT, doesn't seem to happen for the first ~15 mins of driving

What I've done to try and fix:
- Replaced ignition coils
- Replaced spark plugs and wires
- Cleaned MAF Sensor
- Cleaned throttle body valve
- Changed air filter
- Cleaned E-Shaft Sensor

My Car:
- 2005 AT
- 63k miles
- All stock



I'm not sure what else to check so any help is appreciated.

Generating Power at Full Throttle
• Ignition Coils
• Spark Plugs
• Spark Plug Wires
• Engine Compression
• E-Shaft Sensor (ESS)
• Air Filter
• Intake Valving
• Throttle Body
• Mass Air Flow Sensor (MAF)
• Fuel Pump
• Fuel Injectors
• Catalytic Converter (Cat)

Keeping the Engine at a Cruise
• Ignition Coils
• Spark Plugs
• Spark Plug Wires
• Engine Compression
• E-Shaft Sensor (ESS)
• Intake Valving
• Throttle Body
• Mass Air Flow Sensor (MAF)
• Fuel Pump
• Fuel Injectors
• Front O2 sensor
• Catalytic Converter (Cat)


Keeping the Engine at an Idle
• Ignition Coils
• Spark Plugs
• Spark Plug Wires
• Engine Compression
• E-Shaft Sensor (ESS)
• Mass Air Flow Sensor (MAF)
• Front O2 sensor
• Catalytic Converter (Cat)
• Intake Vaccum

That nasty "engine compression" shows up in all three categories..

Plus you've already addressed most of the ignition and intake systems.

Time for a compression test, and start making funeral arrangements.

Clutch neutral safety switch. When you press the clutch in, does it go away?

Sadly, I think you're right. I looked up symptoms for bad apex seals and they are identical to what I'm experiencing. And only 65k miles....:banghead::banghead: My car stalled on me for the first time today going up a hill.

Taking it into the dealer tomorrow to get it diagnosed.

I have a 2004 with an auto as well and am experiencing the same thing. Let us know what the techs find out! Crossing my fingers for the both of us

The compression was measured at 7.4-7.7. That was pre-zoom zoom so I don't think compression is the issue.

The dealer blamed it on compression saying 6.9 was min and 8.5 was ideal. They said I was on the low side (I wouldn't consider 7.4-7.7 that low). I don't think they know what's wrong with it, because the symptoms are getting worse. It is consistently dying at idle now and it's slowly getting to the point where I can't drive it anymore.

They did say there was no misfires.

Guess I'll have to take it back tomorrow and tell them to find the issue.

Just noticed that I have coolant leaking into my air filter. Took a look at the thermostat and it looks like there is a small leak. Could this explain the symptoms?

Uh.. No it didn't. Something else is in your air filter. Unless you got drunk and filled your airbox with coolant.

But nobody gets that drunk, right??

What else is a yellowy-green substance that looks exactly like coolant? :eek:

Speak for yourself.

I'm thinking someone maybe spilled coolant when trying to fill up the reservoir that's right next to the air cleaner...

My car is doing the exact same thing and I have no coolant near my intake. So, i doubt that is the cause. I have noticed that my oil pressure is fluctuating parallel to my rpms when it happens at idle (I have an external OP gauge).

Any thoughts on this?

The only thing that I can think of at this point is that the mechanic didn't do the compression test while it was hot. Wouldn't surprise me...

I am not seeing any issues with the oil pressure.

So what the heck is this substance? Doesn't smell or look like oil?

Ironj221, your compression test needs to include your starter's rpm and your altitude in relation to sea level. You should have gotten three numbers for each face of both rotors, for a total of six numbers, with the starter rpms also. results should be normalized to 250rpm and sea level. Check out this chart below to help interpret your results.

Thanks for the chart. I attached the compression test and some other test they did. I'm at 2,000ft.

Would these compression numbers cause the catastrophic failure that I'm seeing at red lights? It's hard to believe that I could go from a perfectly fine running engine to stalling at every red light in a week. Wouldn't compression issues be more gradual?

I have noticed that turning the A/C on makes things worse. Presumably because it puts more load on the engine.

your compression numbers are probably normalized for your altitude. According to the Rx8 club compression test chart, your numbers show into the green, except on one face of rotor 1, which is in the yellow. You should have a lot of life left in this engine if properly driven and maintained. Therefore I believe your idle issue lies elsewhere.

Keeping the Engine at an Idle
• Ignition Coils
• Spark Plugs
• Spark Plug Wires
• Engine Compression
• E-Shaft Sensor (ESS)
• Mass Air Flow Sensor (MAF)
• Front O2 sensor
• Catalytic Converter (Cat)
• Intake Vaccum

What coils, wires and plugs did you install ? You could have an intake vacumm issue, or a cat issue, or a bad front O2 sensor. I am sure other RX8 owners with similar problems and fixes will post their advice after looking at your diagnostic sheet which may indicate an imbalance in your fuel/air mixture.

They are stock coils and plugs. I'm not getting misfires and it's unlikely to have 2 bad sets of everything, so I think the ignition is good.

There is no glow on the cat. I've sprayed for vaccum leaks, but haven't done a smoke test or anything.

Here are some more diagnostics the dealer gave me:

FUELSYS1: OL - Drive
FUELSYS2: -
LOAD: 0%
ECT: 149 F
SFT1: 0%
LFT1: 0%
RPM: 0RPM
VS: 0MPH
SPARKADV: 0
IAT: 145.4 F
MAF: 0g/s
TP: 16.86%
SAIR_COM: OFF
RUNTM: 00:00
EVAPPCT: 0%
FLI: 29.8%
WARMUPS: 3
CLRDIST: 28.58mi
BARO: 13.195psi
CATTEMP11: 149 F
VPWR: 12.27V
ALV: 0%
EQ RAT: 0:1
TP REL: 5.1%
AAT: 145.4 F
TP B: 33.33%
APP D: 31.77%
APP E: 20.39%
TAC PCT: 7.84%

What those numbers mean are beyond my knowledge. I would assume a mechanic would see any issues with them, but you never know.

Those don't mean much. The engine wasn't even running when they were taken.

That's what I thought. And this is why I don't trust the dealer ran the compression test correctly...

My long fuel trim is 11. Accelerating brings it to 2-3.

Short term is 0.

This indicates a vacuum leak, right? Freaking dealers...

That's fresh oil.
Clean the intake
Clean the MAF
Take the overflow tube from the Oil filler and put a filter on it.
Cap off the Nipple on the intake.
Drink a beer.

Just an update on this...

I had to fight with the dealer but finally got them to admit it wasn't the engine and they called a 'Mazda tech line'. They suggested it was fuel injections. I put in seafoam. I've only driven a half of a tank so far, but no stalls. It seems to be getting better.

Iron 221, yesterday I drove my car from Santa Barbara to LA. While I was on the freeway the car stalled while in traffic, I was able to restart the car and then the problem repeated. I was able to drive home and it stalled on my drive way. Do you feel we have the same problem. Two years ago I had an issue in the morning due to flooding of the engine. I made such a big stink the dealer provided me with a new motor. How do I solve this problem without replacing all the parts your talking about.

Been there done that. That's low compression probably around 4 bars. Time for new apex seals and a rebuild while you're in there.