idle RPM is constant but I feel some slight vibration when idling
 

Not to bring this up again, but I did a search and was having a hard time telling if the vibration I feel at idle is the "rough idle" or something else. I have the M flash, and the RPM holds steady when I feel this, its not jumping around. its not a large vibration, I just feel it through the seat every few seconds.

Is this what people were referring to as rough?

If you have the air conditioner on you will be able to feel the car vibrate every few seconds. This has happened to every car I have owned, very noticeable while at a light.

My 8 has what feels like kind of a stumble, not quite a miss, but a stumble while idling or holding the engine at a constant RPM with no load--which makes the idle a little rough overall. What it really reminds me of is when I had a Mustang with a 289 and a 4-barrel carb and the mixture was too fat (rich). I can't help but wonder if things are still too fat even with the M flash. I've got an outrageous amount of soot around my tailpipes, which I believe is do to a fat mixture.

I've got friends who have recently purchased new cars and they don't have soot in their tailpipes. They are clean and look brand new.

I have the same symptom, can anybody expalin it? Just like RotaMotion said, it seems to stumble every so slightly. I especially feel it going up hills at 35 MPH in third gear, so I drop down to second to bring the RPM's up a bit. It feels like a fouled plug or something. I have the M and the new plugs, and currently I am at 10,000 miles on the OD. Maybe the fuel maps are still not right. I hope Racing Beat gets this all figured out one day.

The vibration at idle is normal (bmmmmmbmbmbmbmmmmmmmmmbmbmbmbbbmbmmmmmm). The soot around the tailpipe is also normal, as a result of burning oil, not running fat.

I tried switching to a mid grade gas to see if that has any effect, is everyone having this issue?

Good point! I hadn’t thought of that :eek: This is my first rotary and I’m still getting used to the concept of intentionally burning oil. Still, I can’t help but wonder if there would be less soot if I had the original 250 hp lean fuel map designed for the car.

I still have some of the early 8 product literature that glorifies increased efficiencies with the 8s 13b by it ability to be run leaner than a piston engine.

Are the Canadian 8s the same as the ones in the states with the exception of the fuel mapping? If so, do you guys see much sooting on the exhaust pipes?

This also makes me wonder if we can get our hands on a Canadian 8 fuel map and put things back to where they should be with more power and better gas mileage. Hmmmm :D

The idle vibration seems to be normal for the RX-8 and is related to fluctuating magnitude and frequency components of dynamic torque at idle. In a perfect world, engine operation at idle woud be perfectly steady, resulting in a constant dynamic torque. The engine mounts would be tuned with this constant dynamic torque in mind, so that the powertrain rigid body vibration modes (natural frequencies), such as roll, aren't aligned with any major frequency components of the idle torque. Seems simple enough, right?

The problem is that the Renesis doesn't seem to have a very steady dynamic torque at idle, which makes tuning the engine mounts very difficult. The engineers did the best they could, but it's just not possible to isolate all powertrain vibration from the body when the frequency components of the idle torque are constantly changing. What seems to be happening with the Renesis is that the firing frequency drops from time to time during idle, effectively causing a drop in the dominant frequencies of the engine reactive torque. Since the engine mounts are tuned for the frequencies associated with "regular" firing of the engine, this dip in frequency seems to excite either the roll mode of the powertrain, or the roll mode of the vehicle on its suspension. This brief and periodic increase in vibration levels can be felt by any vehicle occupant and is perceived as rough idle. (By the way, the tachometers in most vehicles are so damped that they don't respond to quick fluctuations in engine speed. Therefore the tach needle is not a good indication of whether your engine speed at idle is fluctuating significantly).

This still leaves an important question unanswered: why isn't the firing frequency steady at idle? I'll pull some comments from an old thread about this very subject, located here:
https://www.rx8club.com/showthread.p...ight=lope+idle

Posted by oi812:
"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."

Posted by RX-8 friend:
"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."

So, two possible explanations for the periodic interuption of constant firing freuqency are 1) an occasional misfire, and 2) injectors being switched on and off by design.

I hope this helps explain the issue. Unfortunately, there's nothing that can really be done to prevent it from happening. Let me know if you have any questions.

I posted this question in the canzoomer forum, but has anyone with the zoomer box noticed this go away/change/get better etc?

just curious if new maps make a difference.

bump

I never had a problem with this until I got my M flash. Before it idled just fine, now it is a littel rough at times. I also have no experience any change in mpg like every other person who gets this flash. I actually wish I could have my L back, my car seemed to like that one better.

if you look in the Canzoomer forum you'll see a thread i posted about rough idle, mine actually got worse after stage 1.1 install.

would new spark plugs do anything? My car has never flooded.

Would brand have to do with this weird idling too? I noticed that whenever I fillup with Chevron (any octane) I always have the smoothest idle vibrations. When I fillup with Shell, Costco, 76, or any other I get the funky idle from time to time. I don't know what Chevron puts in their gas, but it sure is working fine with my Rotary.

Just a few "cleanup" points. The Canadian maps are the same as the American ones. We get the updates later than you.

Shell gas (here in Edmonton, anyway) comes from the tar sands. It has almost no sulpher in it (the removed sulpher is used to create the worlds biggest sulpher pyramid just north of Ft. McMurray, Alberta). Much better for the O2 sensors, cat, and maybe the engine.

I use fuel with 10% ethanol in it, with good results. On a 3rd gen RX-7.

As far as idle with the Canzoomer box, it is pretty much the same. I've done a lot of comparisons due to worries about the coils etc. The Canzoomer box has no effect on fuel or timing at idle.

RX-8 friend. Thanks for the info.

Old post, to be sure, but I thought I'd add that the stuff on the tailpipe often gets called "smoot" in this forum, for those interested in following up. One solution is NevrDull.