Rough Idle. Completely confused.
 

Hey guys.

I would've posted this in a sub forum but I wanted this thread to get more visibility in the general area where people spend most of their time here.

I'm having an interesting rough idle issue.

I spent a good chunk of time and cash trying to repair the issue myself.

I in the past 3 weeks have installed brand new spark plugs (OEM), and wires (also OEM).

Idle was still rough.

So last week I ordered 4 new coils from OnlineMazdaParts.com which I installed tonight.

Everything went on nice and tight.

I reset the computer then fired the engine up.

I noticed barely any improvement in idle quality. The tach needle stays pretty still around 900, or 800 and doesn't fluctuate rapidly or inconsistently.

The old wires were arching. The old plugs were fouled up pretty badly and covered in a grimy / acidic orange fluid. The coils had severe discoloration on the bottom of them.

So I was pretty confident that all of these new parts would have resolved the issue.

I do notice a difference when going through the gears, but as soon as I let her down to idle I get the nasty sputtering.

I let the engine run in the driveway so I could listen to the exhaust. It's constantly popping. Little crackle backfires.

I will be checking my engine mounts tomorrow to see what kind of shape those are in, but if they are intact I'm at a complete loss.

You know, if the engine was just rough and there was vibration I could safely assume or hope that its the mounts, but the spitting of unburnt fuel constantly and the popping which coincidentally falls insynch with the engines somewhat violent stuttering tells me I may be looking in the wrong direction.

I know that was a big post, but I would truly appreciate some feedback from the more experienced owners on the board.

Thanks for reading.

well to tell you the truth my 8 seems to idle rough around 800 but if it's idling about 1000 or so it stops is that the problem? if you give it a little gas does it still do it or does it stop. If it stops its just your engine almost stalling out like when you almost stall on a hill because you let out the clutch too fast but my exhaust doesn't pop when idling I'd def. try the motor mounts then get back to us with your info! good luck though

Like I said, once I get on the gas and bring the car to about 1000 the engine gets completely smooth and runs and sounds great.

Idling (as in, no pressure applied to the gas pedal) = shitty idle. The shifter itself vibrates a little bit, but the popping of exhaust bothers me.

Also if I listen around the engine compartment when the engine is running it sounds like it's gasping for air. Like a quick sucking sound for every rotation of the rotary. It's coming from somewhere near the firewall though, towards the center of the bay. Not near the intake.

I'm so stumped but some weirdness in me kind of likes troubleshooting stuff like this.

Find a good rotary/Mazda mechanic.

You have a stock intake?
Filter okay?
Bad MAF?
Did you knock off a vacuum line?
Someone with more experience chime in............could it take the computer several cycles(starts and driving) before it re-learns after all the installs.....esp. the coils?

Stock intake. It's clean. I had to take this out today to get at the coils more easily so while it was out I checked it out. It looks good.

The MAF is visually intact. No grime, build up, craps or damage to the actual sensor itself.

It's been doing the sucking sound for a while now so if I knocked off a vacuum line it was a while ago. I do my own oil changes and have replaced the air filter numerous times. So I work pretty specifically around those areas, are their any vacuum hoses around those spots that I should check? And if so, how do I check?

My 8 tends to idle rough as well. Always has, which can be a little annoying. I have taken it into the service shop a bunch of times, and it seems to be normal (hasn't affected anything else).

Has your 8 always idled rough? Or did it just start?

It started getting really bad about 3 months ago.


Now here's the real question because I always hear around here, "rough idle is normal on this car."

Is it normal that the 8 idles rough right out of the factory.

OR

Is it normal that the 8 begins to start idling rough at or around 40k miles.

Compression check?
Motor mount? (I know that seems weird, but there is an interaction between the sagging of the right mount and the knock sensor.)

I don't know how to check compression, but I'm going to go do a search on it right now.

There is a slight knocking now that I think about it. It's faint, but it's there.

no lack of power in any areas correct?? if so i'd say your cat is starting to go.

I doubt it's any vacuum line. I was just throwing out some ideas. See MazdaManiacs concerning the motor mounts and knocj sensor. That seems like it might fit the bill. At 40k that's plausible. Also.............it could be the cat since you hear some other noises.

Yeah I seriously think you're fine like I said it just doing what it does when you don't give it enough gas and let out the clutch starts to vibrate and almost shut off it's like the idle needs turned up like on the old carb cars whent he screw would vibrate out and make the idle RPM go down I say you're just fine. I dont' think the popping is anything to be worried about but as someone said about the cat it prob wouldn't be a bad idea to have someone look at it just to make sure. If nothing is wrong with the cat I say you're 8 is just fine!

Should not have rough idle. Both rotors should run smoothly together - it sounds a little like once you get up to speed, heat and compression are taking over the firing and timing so it runs smoother - so the timing may be off -you may not have the fuel set right, there could be a clog in an injector, one rotor could have carbon build up, the air-fuel ratio is bad (the high carbon build up suggests this), too much oil is being released into one rotor .... But you should not have a mess on your plugs and you should not have rough idle!

Pester Far Side and Rotory God for their input - Swoop also pretty good...

Can you feel it / hear it inside the car?

I was concerned at first when I stood behind my car for the first time while it was idling and noticed it went like "mrmrmrmrmrmmrmrBopmrmrmrmrmrmrmrmrmrmrPop"... I thought "something must be wrong with the idle". But the car run just fine, consumes gas/oil as expected, pulls as expected... went thru a few complete check-up with the dealer and no problem, all is fine. Can't hear it from inside without actively trying to. I also have a bit of vibration in the shifter but every MT car I drove has some.

There might be something up with your car, but I, as a complete paranoiac about the condition of my car (somehow I'm always searching for hints of something meaning big trouble) I can tell you that sometimes it's better for your overall "enjoyment of the car" to just ignore it until there's a real and concrete sign of something wrong (eg: powerloss, CEL, etc).

Yes being cautious and proactive about it can save you money down the line, but if you worry about every little thing you might end up worrying for nothing.

Please show us the old spark plugs.

Several things.

Since your car was running with bad ignition for a while, try some injector cleaner and get it up on a nice long highway run to see if you can clean some possible carbon from the ports.

I had a back fire thing for a while that turned out to be a cracked vacuum hose port on the intake manifold right in front of the oil filter. Needed a new intake manifold to fix that, but it cleaned it right up. It took six months of bad idling before that set a check engine light.

Have you hooked up a scanalyzer? Sometimes there can be stored information without a check engine light being set.

All things clean and running well, the car should not idle rough. My car has gone in and out of rough idle in the 53K miles that I have had it, and rough idle is an indication that something is a little out of whack. Best of luck tracing it down.

My 2 cents......
 

I had an awful idle for quite a while, which turned out to be the vacuum hose for the v-fad.

It's right below the throttle body, and could be heard sucking when I got near.

The solution was that the dealer hooked it up to the reader which showed a "long-term-fuel-trim" of 30% - way out of spec, it was idling really lean because of the un-measured air leak.

The only other thing I could suggest is to clean the MAF (not just the temperature sensor - see the DIY Clean the ACTUAL m.a.f.

S

v-fad............that's what I couldn't think of before.......brain fart! This matches the location of the sucking sound that was reported to be near the front center of the engine bay but away from the intake! More to the left, ya know?

I just took mine out and put a plastic tab on the nipple.

No idle issues whatsoever. the VFAD vacuum is useless anyway.

Those nipples are cheap, 2 bucks can get u 4 at pepboys.

According to my dealer "Your engine is supposed to shake a bit there buddy.". This was after I had the motor mounts replaced and still felt a odd shudder every so often while at a stop light.

Check the motor mounts if you feel as if the engine is vibrating like a V-8. Mine was and now its alright, but not fine I still get the odd shudder which is annoying.

going with motor mounts, and reset your ac amp... it does make a difference..

you dont mention the year, or mileage.. but at 50k miles mine were done.. they have changed the mount also.



beers :beer:

I just (finally - literally 6 hours ago) put a new mount on my right side and OMFG.
I really had just accepted a lopey shifter in this car - especially since the new (and, apparently special) motor did it too.
However, Karl (the QMD dealer tech and club buddy that helped me with the install), pointed out that the mount was sitting too low (sagged) and said that 99.99% of the rough idle issues are solved with the motor mount.
I just kinda shrugged it off, but I figured I had to get fresh plugs so I'll grab the mount while I'm out.

Night and day. The shifter is absolutely still at idle.

The interaction is with the knock sensor. The mount sags, it makes contact, the knock sensor feels it, retards timing, the motor shakes, it rubs harder, the knock sensor pulls more timing. Et cetera.
I have actually seen the interaction with the timing on my logs, but didn't put two and two together until now. I should have, since on my original turbo system, the wastegate canister would occasionally touch the frame and the exact same interaction would occur.

yep,

aint it cool, and depending on how you pulled the motor you ppf might be off. might check it..

beers :beer:

Nah. I've had the PPF out enough times that aligning it (cross-member bolt method) is second nature to me.