Pariah

Hi, to start off, I'm a heavy diesel mechanic with an 05 RX8 6sp. I imported it from Japan with 74k km, and in the 6 months since I've racked up nearly 10k km and had a lot of fun. The car came basically stock and unmolested, although it does have uprated leads and a cute engine grounding kit that clutters everything up. I resisted the temptation to start messing with it until last week, when I picked up a Injen intake.

That's where the trouble started. Prior to that, it had been running beautifully, without any problems. Started fine hot and cold, made good power for a car, reliable, and not too bad on gas really. When I installed the intake, as I always do when working on engines, I disconnected the battery. After making sure that it was installed correctly I reconnected the battery and tried sparking it up.

Now the familiar scene, will idle if started cold and the throttle untouched, won't if you start it hot or try blipping the throttle. I've pumped the brake pedal 20 times, disconnected the room fuse for a couple hours, turned the key with the odo button pushed, given it a dozen hot/cold cycles, held the rpm at 3k for 20 seconds, held it at 4500 for 20 seconds, slowly lowered the rpm manually until it will idle on its own at 750 rpm, but nothing. It revs smoothly and makes good power, but if I rev it up then let it sink back down as I have many times before it dies. Sometimes if I gently lower the rpm it will idle very roughly, hunting between 500 and 1000 rpm. This is incredibly frustrating. I've been working on engines for a decade and around efi systems for half that. I've never come across this before, and as it's my weekend car, it's turned into something holding the carpet in my garage down instead of something to unwind with.

Sorry for the long, whinging introduction, but I just can't take it any more. Any help would be awesome.

RIWWP

iTrader: (2)

^ This is your problem. Remove the intake and put the stock one back on. The only 2 aftermarket intakes that won't cause problems with the RX-8 are Racing Beat or Mazdaspeed/AEM (same intake). Everything else will have idle trouble, CELs, power loss, you name it. Injen isn't as bad as Weapon R or K&N, but it's definitely worse than stock.

Keep in mind that you also reset your fuel trims with the battery disconnect, so it will need some time to re-learn them. Currently, it's having trouble relearning them because you are crippling it's ability to know how much air the engine is actually pulling past the MAF. Our engine is insanely sensitive to things like pipe diameter, distance of straight pipe before AND after the MAF, the screens in the intake to straight the airflow, etc...

Put the stock intake back in and reset everything again. Give it a couple drive cycles and you should be back to normal.

Pariah

Damn, there goes a few hundred bucks. I did some research prior to purchasing and couldn't find anyone with any issues, including a thread on here that introduced me to rx8club so I figured I was safe. Unless it's 16 litres and running 18:1 compression, or 675cc and pulls 13k rpm, I'm out of my comfort zone. Thanks for the help

RIWWP

iTrader: (2)

Use Google to help with searching. Like site:rx8club.com injen intake https://www.google.com/search?q=site...sm=93&ie=UTF-8

Mostly FS threads, which that by itself should tell you something. There are a few threads detailing issues, and one which has a RB vs Injen dyno done, where the Injen lost 10whp to the RB, and the RB doesn't add even 10whp to a stock 8. Looking at the pics of the intake pre-install, I'd bet the problem is how close the MAF is to the filter. Far too close for the airflow to settle down and straighten out.

Pariah

Fair call. I've done enough dyno time to know that back to back doesn't mean a hell of a lot, but that's interesting about the actual power numbers. Bit hard to do a decent search on a phone. I'm very interested and surprised about how it works out idle, just seems like an inflexible engine management system.

RIWWP

iTrader: (2)

No, not inflexible.

Flip the perception around a bit. The basic engine design/configuration of the 13b used to only put out around 110hp. Mazda has adjusted and tweaked everything to get it to a razor's edge of how much power they can pull out of the same basic 1.3L engine, and they have over doubled the original hp. A lot of R+D went into squeezing this much power out of the tiny engine, and companies that just slap something together typically make it fall off that razor's edge of peak performance, and the impact is considerable. Think of the engine as already modded to nearly peak N/A HP, and you will start seeing how it's hard to get any gains, and easy to create losses.

Pariah

I absolutely see your point, and having looked at the various systems in my 8 compared to, say, my Street Triple, it's almost motorcycle level technology while still being hamstrung by modern emissions standards. I do have to say though, even a bad idle is preferable to none. In almost every EFI system I've worked on, from race bikes to CAT power packs, there's been a backup idle tune that might hold it at 3000RPM but will still allow it to run. I've seen VE distributor pumps a full fifteen degrees out and the bastard will still run, albeit badly. It doesn't really matter, I'll throw the old intake back on once I've replaced the vacuum line elbows and go from there. All I was really after was a nicer induction roar, the Triumph has spoilt me for that.

RIWWP

iTrader: (2)

Getting the RX-8 to pass emissions was hard enough without having an option for a high idle

You are absolutely correct about the emissions hamstringing. The only two areas where you can get a relatively proven noticeable power gain are both related to emissions. Cat delete and a re-tune that ignores emissions targets. If you are looking for some better intake noise, look around for clips of the Racing Beat and AEM to see if they meet what you are looking for.

Pariah

The difficulty I have is with getting access to the parts. Shipping costs to NZ are unbelievably expensive, to the point that it's actually a better option to wait for something to come up, or find and replicate a design from the internet. I paid $150 for a set of show bars for my Triumph to come from the states. That doesn't include the $500 I paid for the machining, anodizing, and materials. This is such a huge change from my last car, a sleeper '78 Mini that did high 14s, I'm a little overwhelmed.

RIWWP

iTrader: (2)

I recommend stepping over to this subforum: Australia/New Zealand Forum - RX8Club.com

They will be able to help you with sourcing stuff, since they have been dealing with the same challenges for a while. Brettus especially should be a gold mine of useful knowledge.

VaultNrd

So as you can see its been quite sometime since anyone has made a post here,but its the year 2023 and iv'e went a head and purchased myself a Mazda 2005 RX8 with 70k miles on it,been running absolutely perfect.
I decided to put in a fresh battery because it seemed the old one was wearing down.Well fast forward fresh battery is installed and all is well I thought ,started up fine and let it idle for 12 mins or so as soon as I took it out of my parking space and got to the stop sign on my street noticed my Rpm's drop and the car died.
Performed an ECU reset and the idle is fine when parked ,not sure how many times I need to do this but either way its going to a mechanic to be checked out.Like I said car was just running fine so I have no reason to believe its the engine considering its low mileage.I was reading on here that after pumping the break 20 times when the car is cold ,turning the engine over and letting it warm up (obviously) to operating temp ,and then waiting 10 -15 mins that it would reset ,also stated that it needed to be revved to 4500 rpm for 20 seconds and 2500 rpm for 20 seconds to complete ECU reset.This is a real pain in the ***.There are some other things I haven't tried like cleaning the Mass Airflow Sensor .I will post an update if I can get the idle fixed but other wise if anyone has any advice im all ears.

Loki

iTrader: (1)

Stop resetting it and let it learn
Never heard of the 2500 and 4500 revving procédure, just restart it if it dies and keep driving.

If you have an aftermarket intake that could play into this. But you're actively preventing it from learning.