Why does the renesis "lope" at idle?
 

You all know what I mean... kind of a lope or lump or just generally not a smooth idle.

Can someone explain this to me? I would think it would be perfectly smooth, kinda like an electric motor whirring away, but it's not. Is it fuel delivery problems, or some function of how the rotary engine runs?

Rotarygod? MazdaManiac? (etc) Any of you experts listening?

I was long wondering about the same thing.
Those little hiccups during idle sound like the car is kinda misfiring... why is it not as smooth like at high revs? Strange.
My ten years old Ford Probe GT with 128K miles seems to have a smoother idle.

mine purrs. No loping here.

Yea, every time I sit in the car waiting for a light w/hand on the shifter, I ask myself the same question.

Then again, I think the whole car feels a little 'rough' in character when going slow too. It definitely smooths out wonderfully after getting up to speed.

Perhaps it has the 'exotic-car' trait of being much more at home at high speeds/high RPMs where it can stretch it's legs? :)

doea anyone here have the K and N, becuase that has a history of a rough idle. Mine runs just as smooth as any other car that i have ever owned, maybe even smoother.

You know what people are thinking- that your car "lopes" but you're just not cognizant of it.

What we need is for someone whose car "lopes" to check out in person someone else's car that supposedly doesn't "lope."

I noticed the "lope" since I got the car in September, now with the Borla, it's much more noticable. I always wondered if it was just mine!

FOr those that believe your engine does not "lope" or "surge" at idle:

Look at your shifter knob. If it moves at all while the car is idling, your engine lopes.

I wonder about the auto people since so much is different in their vehicles.

The loping is mostly due to the inability to reach a satisfactory mixture at idle.

Idle is the most inefficient RPM range for any engine and it is even more so on the Renesis.
In order to keep the emissions as low as possible, the PCM runs the motor very lean at idle and reverses the ignition sequence to effectively advance the ignition to make up for the -5° or so retard that takes place.

It is suprising that the motor idles at all!:p

How could anyone miss it if their car lopes? I know smooth . . . I know purr . . . I know steady . . . a tach with a steady rpm at idle isn't loping.

Unfortunately, that isn't true.

Loping is not a change in RPM and the RX-8 tach is to slow to report any fast variations in RPM if they existed, anyway.

ok. So if one can not know if one is loping or not . . . since a smooth steady idle and a steady rpm are not evidence of a lack of loping (no little hiccups or the other descriptions used on the thread) . . . then how can anyone possibly say they aren't loping . . . and if that is true why would anyone ask the question to start with since the only acceptable anwers seem to be 1) yes or 2) no way for me to tell so I don't know. (unless of course I have equipment to test for "loping" but I thought the question was based on sense rather than mechanical measurement.)

If you hear your exhaust popping at ide, it lopes. It is more pronounced when the engine is warm.

You are saying that there is absolutely no movement of the gear shifter at idle?

what do you mean by "movement" mine vibrates but doesn't move to my knowledge.

That would be movement.

In my old 1st Gen 7, (carburetted - no EFI) the popping sound was backfiring. Soft and subtle, but backfiring none the less. It did it for the life of my car, and was due to the ham handed emissions systems on the early models.

Perhaps the 8's rich mixture is igniting in the cat?

Every manual I've ever had, the stick vibrated at idle, the backfiring is the nature of the beast according to the service tech.

On my previous car ('93 FD) I noticed a bit of this...when I think of a "loping idle" I was thinking of something more rhythmic...occasionally the FD would sound a bit like a miss, but it would generally stay steady. It has done that for as long as I can remember. I haven't really noticed it so much with the 8, but the shifter vibrates a lot more. Now, is that a lope? Its constant, and way too quick to be considered irregular, so I don't think so. Now, I'll have to go listen for anything else. The exhaust on my FD was MUCH louder, so that undoubtedly made it more obvious than on the 8.

jds

Well, I think we are using the term "lope" incorrectly, which is why I put it in quotes in my original post.

There is a wide array of what is considered "smooth" since it is an aesthetic judgment.

It is also important to note that this "lope" is not a problem of some sort, just a characteristic of a running motor, regardless of design.

i dont consider the vibration of the stick "lope". the shifter is directly connected to the tranny hence the vibration. this has nothing to do with a "loping" idle.

I think the problem is that "loping" hasn't been sufficiently described. What I thought Omicron was referring to was a intermittent yet very noticeable fluctuation of engine idle vibration levels in the cabin, i.e. pitch or roll of the body, shift lever vibration, seat vibration, etc. Idle may seem smooth for a few seconds, but then seems to transition to a rougher idle, then back to smooth, and so on.

Since I consider myself to be relatively knowledgeable about this subject, let me point out a few things:
First of all, there is no such thing as a perfectly smooth engine, as you probably all know. Even a rotary engine with no reciprocating parts will not have a perfectly smooth idle. If you look at a time trace of engine speed or flywheel torque versus time, there is oscillation, or a so-called dynamic component, due to explosions of the air-fuel mixture, exhaust, intake, etc. I'm not sure how the magnitude of this dynamic component for rotary engines compares with gasoline engines, however. For instance, diesel engines have a much larger dynamic component than gasoline engines, and hence are much harder to isolate from an NVH (noise, vibration, and harshness) standpoint. I would imagine, in fact, that the dynamic torque from a rotary engine is similar to or higher than that of a piston engine since it generates a similar amount of torque with a much smaller combustion volume. Someone please correct me if I'm wrong--I'm a rotary newbie.

However, dynamic torque generated by the engine is only half of the equation when it comes to a perceived "rough" or "lopy" idle. The other half depends largely on how the powertrain is isolated, or mounted. A good isolation scheme can make even the roughest of engines appear smooth to the driver, while a poor isolation scheme can make a smooth engine seem extremely rough. This is a complicated issue since tradeoffs must be made among cost, NVH, packaging, and durability when the powertrain mounts are being designed. It's a compromise that doesn't always yield an optimally tuned mount.

Also, manufacturers employ a number of measures to quantify the interior NVH quality. The most important ones are usually seat track vibration, steering wheel vibration, shift lever vibration (manual trans), and sound pressure level and spectral contents at the driver's ear. I think Mazda did a great job with respect to most of these measures, with the exception of the shift lever vibration. (MazdaManiac--the shift lever in any vehicle would vibrate if not properly isolated, so it's not really an indication of "lopy" idle). I had a '90 Integra that had an insane amount of steering wheel vibration, shift lever vibration, and wind noise. (In general, Honda lags behind the rest of the industry when it comes to NVH, but they are improving quickly.)

As for my opinion on the lopy idle: if my interpretation of what Omicron is describing is correct, I have the same issue. The idle seems really smooth for a period of time, but encounters some rough periods that can definitely be felt in the cabin. It's difficult to say what exactly is happening since the PCM employs a rather complex control scheme. It might be related to changing air-fuel mixtures, or it might just be interaction with the various engine accessories (water pump, compressor, power steering pump, etc.) that create a constantly varying load on the engine. Any number of factors would change the vibration characteristics of the engine, and it's not always possible to design an isolation scheme that will sufficiently attenuate interior vibration levels for all of these cases. Overall, I'm happy with the NVH characteristics of my particular RX-8. If some of you believe you are experiencing more extreme symptoms, it's possible you might have a problem, however.

Thanks RX8_Buckeye. That was awesome and very concise.
I think you nailed the issue precisely.

Thanks MazdaManiac. Hopefully it helped explain some of the idling issues.

If you want an extreme example of loping idle, listen to a V8 with a 3/4 or full race cam. Radical swings in RPM due to the cam being designed to be optimal at higher rpms only.

Since the rotary has no cam, the loping is most likely tied to the PCM and the intake system. The PCM theoretically can be designed to be optimal at all speeds. The intake system is designed for three distinct rpm ranges but is suboptimal at idle.

Oh yeah, mine lopes significantly. Hard to tell the exact rpms, but I would say it varies between 900 and 600 rpms.

Have you ever heard a bridge ported rotary at idle? That's the most beautiful music to my ears! BRAP, BRAP, BRAP...

Is this what you mean by loping? I don't own an RX-8 but when I test drove it several times now I thought it had the smoothest idle ever!

My protege5 shift knob also vibrates at idle (or any other rpm), does this mean I have rough idle?

What I don't like about the piston engine sound is the rickety-rack of the valve train, awful!

My 8 definitely does not sound like a bridgeported rotary! Overall I consider that to be a good thing, but it would be cool if you could do that "on command" at stop lights. Well...maybe it wouldn't... :D

Btw, I haven't taken off the shifter knob, but on the FD the knob was actually pretty heavy, I think in order to reduce vibrations. Judging by the vibration of the knob in the RX-8, I'm betting this one isn't so heavy. I always thought it was ironic for Mazda to brag about the weight savings in the drilled aluminum pedals, when they added a lot more weight than that in the shift knob for no really good reason.

jds

When does your car rpm hit 600? I've yet to see mine go below 900.

Yep Buckeye, your description of "lope" is pretty much what I was describing.

What you say makes sense, but I also only partially buy the "good NVH isolation" argument, as I can hear the lope as much as anything. No amount of NVH work is going to solve that. I guess what I'm wondering about is why there is no discernable pattern to the lope. In the case of V8 engines (without a radical cam), there is a definite thrum-thrum-thrum. V6's have the same thing to some degree but they come at greater frequency, so they seem to idle smoother. In fact, I've had V6 powered cars that idle so smoothly that you cannot tell they are running without revving it. Even 4 bangers seem to idle with some definite pattern to it. But not the renesis-rotary. I've had 2 RX-7s over the years, and have never noticed this to the same extent that I do in my '8.

I have noticed that if I give it just a tiny bit of gas at idle, enough to raise the RPMs up to 1000-1200, the lope pretty much goes away. So I wonder, "how much more fuel would I burn if my car idled at this RPM?"

It's no big deal, I don't think anything is wrong with the car or anything, it's just something I wonder about when idling at a stoplight.

I have taken mine off, and it is definitely heavy. Feels like it's filled with lead shot or something. FYI.

checked my shift vibration the whole ride home from work . . . at stops and lights and after pulling in the garage and it still purrs smooth and even. Of course if "loping" is defined as any vibration that can be felt when ones hand in on the shift then it lopes and the whole car lopes and I lope when driving . . . but I still would respond that I don't lope . . . smooth and steady idle. Any vibration is minor and even and I can't imagine any car that has NO vibration in the stick. (of course assuming the engine is on). I have drove a five speed Rx7 for 16 years before the Rx8 and also had two other manual tranmission vehicles and none of them ran or idled as smooth as the 8.

My car lopes at idle, I think it's a partial misfire every once in a while, it's almost like the combustion process is not 100% constant at idle. I'm not talking about a huge misfire, just enough to "slow" the crankshaft rotation for a split second. I feel there is some additional small amplitude vibration while at idle due to the engine mount tuning, but the "lope" causes an inconstant low frequency "shake" or higher amplitude side to side shift lever movement.

While I agree with RX8_Buckeye on the engine mounts and the NVH issue, if it was purely engine shaking forces and the vibration tuning of the mount system, the shift lever vibration would be consistent and cyclical all the time for a given RPM. This would be true if the vibration was torsional (as RX8_Buckeye describes) or transnational (shaking as in a piston changing direction). This is assuming that the combustion process was consistent and uniform each time the rotor fires.

From my experience with piston engines, if the EGR (Exhaust Gas Recreation) leaks at idle, you always end up with a loping inconsistent idle. The normal EGR operation on piston engine is to have the system closed off most of the time and once fully warm and at a low engine load then the system allows a small amount of burnt exhaust back into the intake manifold via a valve. This reduce fuel consumption on the highway by "diluting" some of the intake charge. Less "good" air in the engine reduces the amount of fuel needed. Less fuel = less emissions. Works well at moderate RPM, not so good for smooth idling. It's kind of like the "race" cam beachdog talked about where the intake and exhaust timing is causing some "mixing" of the two cycles due to valve timing overlap.

According to Mazda's marketing literature, the Renesis has built a built in "EGR system" by virtue of the side exhaust ports. Some small amount of left over combustion gas is carried from the tip of the rotor into the intake charge of the next cycle. The thing with this EGR layout is that it is "on" all the time even at idle, even when cold.

So in my opinion, the shift lever vibration the you can feel and see is a combination of some small amount of engine vibration / engine mount tuning and some inconsistent firing due to the side port design.

part of the problem is idling at 900 rpms means the rotors are only going at 300rpms. This means low energy storage when combined with a low inertia engine, and add the lean conditions at idle and it makes the engine have to work harder to keep spinning and overcome compression.

also the 300 rpm rotor speed is putting out frequencies very close to the low lying resonance frequencies that all engines have. This is why every car on the market has some shaking involved during start ups and shutdowns of the engine because you have to go through the resonance frequencies - only in those examples you get through the critical frequencies quickly instead of sitting right at them.

I like the low-inertial-mass theory. Makes sense that that would make any momentary bumps more noticeable. Mine feels like a missed or partial combustion that happens every couple of seconds or so. Not big misses - fairly subtle. purrrrrrrrrrrrrrrrrrrrr(bump)purrrrrrrrrrrrrrrrrrr rrrr(bump)purrrrrrrrrr(bump)purrrrrrrrrrrrrrrrrrrr rrrrrrr

The engine by itself does not have natural frequencies anywhere close to 300 rpm (5 Hz). The "low lying resonance frequencies" that you refer to are the natural frequencies of the spring-mass system that is created when the engine is mounted to the vehicle. Engineers carefully design the mounts so that these natural frequencies are not aligned with the excitation frequencies of the engine at idle or other natural frequencies of the vehicle--such as suspension modes and body modes. As you stated, there is no way to avoid exciting these resonances during engine start up or shut down. However, it is highly unlikely that the Mazda engineers would design a mounting system that has a natural frequency aligned with rotor speed at idle if it could be avoided. Maybe, however, it is difficult to manufacture a mount with such a low stiffness that meets durability requirements.

So I guess we've decided there isn't anything that can be done about this?

if it's not broke..

My AT lopes at idle. As somebody else mentioned, it almost feels like an occasional misfire.

Yeah, there really isn't a "solution" because there really isn't a problem.
Its just a feature!:p

I found it odd myself when i got my 8. My first gen (83 GSL Limited) was so smooth and quiet at idle I would often think i had stalled it when sitting at a light. I expected the renesis to be as smooth but it is not. It's as smooth everywhere else. Just not idle

Nothing like being on a date and cranking the starter on an already running car.

You guys spend far too much time idling and not driving ;)

Mine behaves just like Nubo's (though I think his RX-8 is bee powered!). I put it down to an intermittent misfire. It's worse in protracted stop go traffic and was definitely worse prior to PCM rev "L" and "M" when it would foul the plugs so badly it was prone to stall.

I'd be very interested if anyone has an RX-8 that doesn't have the Nubo behavior. I'd also like to know how your cars with lightened flywheels behave. My guess is that the effect would be exaggerated.

Listen to the injectors. They cycle. In a perfect world, an idling engine's injectors would be operating in a constant rythm. As Mazdamaniac stated, the poor idle is a result of the design. The injectors can handle a lot more fuel than we are using, even at full load full throttle we see only around 30-40% duty cycle. What this means is one injector pulse will be too much fuel for idle, so the PCM shuts them off, then uses them, then shuts them off... etc. We saw the same thing with the 3rd gen RX-7 when owners replaced the injectors with much larger units (to handle higher boost and larger turbos). Their solution was to bump the idle up.

We've also seen the different flashes affect the idle. The current one (M) sometimes idles rough, other times smooth. We haven't been able to correlate it to anything yet.

MY old Rx7 did it and the new 8 does as well.. its just the way it is.. like algabra...

I don't spend time idling by choice. Bumper to bumper traffic makes for a lot of idle.

I'm not complaining either. As long as it doesn't idle itself into a stall, I don't care how rough it runs.

I have the same simptoms but I have noticed that reving to 1000 Rpms gets rid of 90% of the bad idle issue. I would love to see Mazda addressing this issue on their next PCM upgrade. I do not know if this will ever happen due to emmissions but it is a wish.

Hi guys, I notice that no-one from Oz has responded to this thread and it's probably 'cos we have not experienced this problem down under. All our cars are hi power, and we have a different flash on our PCM's.....My 8 came from the factory with the "F" flash in Jan04, the "G" flash has just been released. The guy's who have had the reflash are reporting a slightly smoother idle and better economy, these guy's have reflashed their 2003 models which had "E" from the factory.

Just another theory to throw into the mix.....

Regards Gomez.

Actually it just started doing that about two weeks ago. When it drops that low it really sounds like it is going to stall but it always pulls out of it. There doesn't seem to be a definable pattern. I'm just guessing that it is initiated by misfires happening in too quick succession.

I'm keeping a log until I can get to the dealer. I don't want them to say "no non-conformance". Clearly this is a new behavior wich didn't exist previously, so, it is a non-conformance.

My 8 definitely idles differently since the "M" flash. I have an August build and went from the stock flash right to the "M". Upon starting the car I get exactly 2 misfires and then it settles down, that was there before and after the "M". Before the "M" I had a rough idle which only disappeared after some real hard high speed driving. Also the car loped sort of like:
chirp - chirp - chirp - lope - chirp - chirp - chirp - lope
Now after the "M" flash it is more like:
chirp - chirp - chirp - chirp - chirp - Loooooope - chirp - chirp - chirp - chirp - chirp - Loooooope

Again, thanks Omicron for the word "lope" or this post would not have been possible

Which fuel injectors fire at idle speed? If the injectors were smaller, would that fix the idle issue? I understand the need for larger one's if your going FI, but it would seem that smaller injectors (for the ones that control idle) would allow for better precision fuel management.

Now that this thread's already been dug out of the grave....

In this whole discussion nobody mentioned that the plugs fire in reverse order (trailing/leading) at idle, as I've read somewhere on here. That's probably a contributing factor as well.

Also, I'd describe it as more of a 'miss' than a 'lope'. A 'lope' is what a Harley sounds like, or a Continental IO-550 on a Beechcraft, at idle. :D

Well, it depends on what weight you define heavy as. The stock shift knob is really quite heavy, at least in my (subjective) opinion. I have an all-aluminum Voodoo shift knob, and it probably weighs about 1/4 as much as the OEM knob. I haven't put either on a scale -- again, just speaking subjectively here -- but if I had to guess, I'd say that the OEM knob weighs in around 2 pounds.

Bill