My car has an even rough idle.
it always had a bit of a rougher than normal idle because of the K&N intake. That was an uneven roughness though.
If this were a piston motor I would say a sparkplug is fouled, that kind of even rough idle.
I am not getting any codes from the ECU and no CEL.

What I have tried so far:
Replace Coils with new OEM coils.
Replace Sparkplugs
Replace sparkplug wires
Clean Crank Position sensor.
reset crank position sensor (Brake pedal 20 times)
Oil level is good.

Once the engine RPM gets above 1200 or so, it smooths out. There does not seem to be a performance drop.

Fuel Mileage has gone up, from 17mpg around town to 19mpg and from 19mpg on the highway to almost 22mpg

I have 162,000 miles on the car.
the engine was changed out under warranty at approx. 32,000 miles

My theory is one of the apex seals is going bad, so there is blow-by at low engine speed causing low compression on one of the rotor faces at idle. when the engine speed is up, the blow-by is not enough to drop the compression and it would run fine under this theory.

How do I test for compression on a Rotary motor?

What else should I check?

If it is an apex seal, how long before it completely fails?

 

Any dealer will perform a compression test for you, or if you know someone with a compression tester for a rotary engine then you can do it yourself.

I had a rough idlewhen I first bought my car

 

Because I wasn't driving it hard. If you're not regularly getting the RPMs up you can foul your plugs. If you're trying to get good gas milage, that might be your problem.

 

Rough ideal as in rpm jumping up and down or shaky body?
Rough idle is mostly (not always) caused by intake component, check your MAF or any vacuum leak yet?
If you have low compression, it'll get low mpg and feel lost of power around certain rpm.

 

Rough idle as in shaky body. it holds a pretty steady rpm, dipping every now and then if the fans or ac turn on which is normal. but the whole car shakes evenly at idle.

I pulled the MAF to see if it was dirty and it looked clean.
I will look for vacuum leaks.

 

sounds like a motor mount, if I am understanding you correctly

 

It's only shakes 800-1,000 then above it smoothes out. Sea foam with me and see if problem solves Saturday.

 

what time saturday? I am shooting girls in latex from 2pm to 6 or 7 pm

 

My 2004 has done that for years, even after new motor, coils, plugs, wires, air filter and cleaned MAF... and even new engine mounts.

It doesn't "stumble" or wander revs, I just feel the whole car vibrating a bit once it settles into it's lowest idle around 750-800 rpm. At 900 or above it's fine.

A lot of people seem to experience it, leading them to ask if there's a simple way to adjust the idle just a little higher... but apparently no easy way. Frustrating, as it just takes an extra 50-100 rpms to smooth it out.

 

I think it is a vacuum leak somewhere, my latest wild *** guess...
It seems to be running lean throughout the RPM range.
either that or a marginal O2 sensor

 

FWIW, my O2 sensor was replaced too

 

my 04 idles fairly rough too, especially with ac or lights on

 

Motor mount period.

 

Well, to test the motor mounts, a Mazda TSB says:Has anyone tried this? Mine very noticably takes up "slack" when I do this before it starts accelerating again. Like a half-second of nothing, as if everything needs to twist a little before becoming tight again. I just assumed that was normal since I have nothing to compare it to.

Anyone try this and still get an instant response to pressing on the gas?

 

I'm gonna try that in mine today mine is ideling rough as well it also has hard starts I put new plugs coils decarbed and cleaned thbe fuel sys it started ideling rough after a run at a meet.... hard starts came with the car xnt know what else to do about that

 

I think anyone reading this thread today will try this, I will