Rough Idle, Plugs and Wires at 35k Miles?
 

I purchased my 04 MT6 RX-8 a few month ago with 30k miles from a Mazda dealer. They said that they had performed all 'required checks and recalls'. After a bit of research on RX8Club.net and at my local dealer I found that almost none of the recalls or TSBs had been performed (A/C was/is terrible, uneven brakes, very old flash, etc).

Since I got the RX I have had several recalls done with a few TSBs in process (brakes, A/C). I have replaced motor oil, transmission fluid, and rear diff fluid (Mobile 1 all around) as suggesed. However, idle remains rough and uneven.

Two weeks ago I installed the RB cat-back. The idle is the same but much more noticible now when the engine 'misses' a beat.

My Miata needed new plugs and wires at about 30k miles. Is the RX the same? If so, what are the 'best' plugs and wires for the RX? I'm good with a wrench but don't have any 'special' tool for a rotary. Is this a DIY?

Thanks in advance for suggestions, advice, etc.

scheduled sparkplug change is at 37.5k miles, iirc. although some people have found that they needed to change theirs much earlier.

here's a DIY on sparkplug removal.
https://www.rx8club.com/showthread.p...ght=spark+plug

oh, another thing is...the plugs for the rx8 are really expensive comparitivly. it will most likely cost you ~$100 and $120 for a set of 4.

I asked the Service Manager at my local Mazda Dealer yesterday about the rough idle (the RX was in for new rotors/pads under warranty). He claims the rough idle is caused by bad gas produced by Shell and Arco. I said I often use Chevron - of course he then added Chrvron to his list of bad gas suppliers. His recommendation is 76 or Valero.

My recommendation is a gas mask because there was so much BS on the floor it was starting to smell bad.

Does anybody know if there is any truth to the 'bad gas' story?

He said I would get a CEL if the plugs had any problems and did NOT recommend replacement.

My 66 Mustang GT with a lumpy cam idles better than my RX.

Any other ideas on the idle? Like others have reported, when warm it idles at about 800rpm but has frequent but not regular 'drop outs' where the engine sounds like its going to quit then catches itself.

Thoughts? Ideas? Wild-ass guesses?

Thanks in advance.

As you have concluded, that mechanic was full of crap and displaying his ignorance. Gasoline from the major producers is not "bad gas". You can get a tank of bad gas from a contaminated underground tank at a specific station, but that certainly doesn't mean all the gasoline from that brand is bad.

And, as far as I know, spark plugs needing replacement will not directly cause a CEL unless they cause a misfire that triggers a CEL. Generally, ya gotta take them out and visually inspect them to see if they are fouled or worn out. That is, unless you can determine from an electrical test that they aren't firing.

As far as the character of the idle that you describe, that is the characteristic of the idle in these cars, generally. There will normally be a bit of vibration at idle in the shift lever and a minor loping or cycling, but if you are experiencing unusually strong vibration, in the shift lever and seats for example, the problem could be a faulty motor mount. A few owners have had their motor mounts replaced for this problem and there are several threads related to this very problem so do a search of the forum and read those posts. Then find another dealer to service your car.

The fact that he said Shell was "bad gas" is proof enough he's a flaming liar; a clueless idiot; or he's deliberately trying to con you in order to avoid the expense of replacing the plugs. I and probably most RX8 owners on this forum use ONLY Shell gas. I tried all the brands available in my area when I bought the car 2 1/2 years ago (hard to believe it's been that long already!) and Shell performed the best. The cheap off-brand gas stations had the worst gas; of the major brands, I found Arco ran the worst. My preference in order is: Shell, Chevron, Texaco, 76.

I just now have 36K miles on my car and I'm noticing some idle issues and it doesn't accelerate smoothly to redline like it used to so I'm pretty sure it's the plugs. If the plugs are firing unevenly or some are producing a "weak" spark compared to others, that will absolutely affect the idle. Tell your dealer to perform the REQUIRED 37k service which includes replacing the plugs as per Mazda's own service schedule.

Also, if I remember correctly, Shell and Chevron are one of the top rates gasoline suppliers there are and that is based on the Top Tier rating system that some of the auto manufacturers have started using.

Old Spiff is right, you might need new plugs already, but if they won't replace them under warrenty then do it yourself, it seems to be a rather easy job, the hardest part being just reaching to get them. I would also advise that if you have to do the job yourself there are a couple of threads on this board that point you to a much cheaper cost for the plugs than the dealer's $120+ cost. I think there is a site like http://www.sparkplugs.com/results_ap...1&AAIA=1416844 that you can get them for around $80. You will need 2 of each of the premium class NGK plugs.

Just so you know, my car has a lope to it, which is slightly worse now with the "R" flash, but nothing that makes the car rock or anything like that. The shift know will always vibrate, but you can feel a little bit of the motor vibrating by just sitting in the seat with your hands on the wheel in my car.

Thanks for the link to SparkPlugs.com. Very nice. Any performance/reliability advantage in the Denso 'Ultimate/Racing Class' plugs?

I know, I know, Search... From what I conclude the Denso plugs are for racing applications only and the OE plugs are best from street use. Got it. Will DIY ASAP.

The new flashes should fix the rough idling. Many people have had sucess with idling issuses when they added aftermarket air intakes.

^^^^ In particular, adding Racing Beat's REVi Intake seems to help with smoothing the idle.

I wish I knew what was considered rough idling. My cars idle has gotten much worse over time. Now I have 22k on it and the whole car shakes and you can hear things rattling underneath it. The dealer won't even look at it again, they say it's normal.

I looked at the motor mount in question and it appeared fine. I'm so sick of going to the dealer to try to have things fixed, I have just decided to live with it, which I am sure is their plan. People that ride in the car comment on the idle though, it's embarassing. I should have bought a Honda.

at 22K you might want to consider a set of new plugs, especially if you've had the car for a while and its gone through several reflashes, I think the original rich condition can foul the plugs really easily.

If I was you I would check / do the following things, which seem to help me.

1. Run a bottle of redline fuel treatment though the car
2. clean the MAF with some electric component cleaner
3. replace spark plugs with new updated plugs.

is there a difference with the A/C vs. off. With my A/C off, the vibration is much less, with the A/C on, I acutally get a studder every few seconds.

The issue is that the idle runs really lean (14.5:1), when I richen it up witht he megasquirt, it smooths out quite a bit. I'm working on finding a way to fix the idle issue with our ECU project.

Brillo,

Thanks for the advice. I'll try the injector cleaner and clean the MAF. I'm hesitant to replace the plugs, because of the expense. If they were normal plugs, I would just pop them in. I'll check around on prices and make a decision after I try the fuel cleaner and MAF cleaning.

This is more of a longshot, but there is a TSB for a new passenger side engine mount as the cat runs right through it and the heat was causing some to crack and break. Now, that would cause the idle to be really bad, I would think the dealer would notice that, but I just wanted to through it out. unfortunately, I don't think its something you can really see with the naked eye, as its damage to the inside of the mount.

The manual states that the plugs need to be replaced every 30K or so, which is expensive, but not unusual with this car (FD's needed them every 20-30K or so). You might be able to get 40K out of a new set, as now that the afr mix is alot leaner than when the car came out, they won't foul as quickly. Regardless, they aren't going to go to 50K without drops in mileage and a rougher idle.

Brillo,

I think I am going to try another dealer, this will be my 3rd. The current dealer has been rude and unconcerned about the problems I have. I looked at the engine mount, but if there is nothing to really see, it could be it.

Replacing the plugs at the regular interval is not an issue, especially since I have the "free" 5 year 50k mile servicing. I received that since the car did not make advertised horsepower. I doubt they will replace the plugs under this agreement.

Go to another dealer; one that cares about "you" the customer instead of themselves and how to get out of doing anything. I get so disgusted with lazy, excuse-making service people who will flat-out lie to your face rather than simply take care of an issue/problem for you.

It would be real easy to test this; have the service manager go with you to a NEW RX8 sitting on their lot and sit in it with you and start it up. How does it idle? Smooth? Then go with you to YOUR car and sit in it and see if there's a difference in the way YOUR car idles. That would take a whole what....3-5 minutes? If the difference is as dramatic as you say it is and I believe you, then that's all a GOOD service manager needs to see. Take care of the customer.

well just to make a point if u wanna save urself some money, if u dont have $100 bucks or so for a new set.....periodically take the plugs out urself n clean them, thats what im gonna start doin until i reach the point to change them

just curious but doesn't that white on the plugs mean youwere runnin kinda lean? might be my piston brain thinking but o thought a lil browm was good white = kaboom soon

The color of the center insulator is what tuners use to check the air-fuel mixture. A brown to light brown is the color they look at for a proper air-fuel mixture. Black color on the insulator is an indication of an overly rich mixture. Glossy black could indicate an oiling problem and a matte black a fuel-rich mixture.

The light-colored carbon deposits on the bottom of the plug that you see on these plugs are not particularly useful for air-fuel mixture analysis and they generally have no significant effect on engine performance.

As an aside, when you "clean" the plugs, it's primarily the center ceramic insulator that you want to get clean, and that can obviously be difficult to do unless you have a sandblaster cleaning device.

It's not really white, more of a light brown to grey. The thing I am curious about is why the leading plugs have more of a buildup than the trailing? I am not that knowledgeable on this subject. My 8 wasn’t running badly before the change and I do track my car so it does see redline. My only reason for the change was reaching a nice round mileage number (50,000)

I would think that this because the leading plugs do basically all of the work, the trailing plug is just there for cleanup so to speak. I could be wrong though.