How does RX-8 control idle??
 

Well,

I'm curious how RX-8 controls idle?

I'm having some issues with my idle and start up..

Here is my problem and what I have done so far...

My car died on me on the interstate couple of times during my trip to New Orleans...

I got the latest PCM flash by local mazda dealership..

Then replaced my plugs with new plugs. couple of weeks later, new wires and coils (all 4).

A week after new battery.

2 weeks later HKS twin power.

I'm still experiencing the same cold start idle issue. When Engine is completely cold (morning start), the idle will hunt and sometimes the engine will die. after couple of attempts and engine warms up a bit, car runs like a champ!

I figure best way to trouble shoot is to find out how idle is controlled on RX-8.

Anyone can explain to me?

I'm thinking it might be the O2 sensor.. and also grounding of the engine.
If O2 sensor, has any of you had issues with the sensor?? what kind of symptoms?
Can you clean the sensor?? Which one to replace for idle?? Both pre and post cat?

You pulled your battery a week ago. hmm

there should be enough drive cycles so.

if u're still under warranty, u might want to tell dealership to check it out for you. it could be O2 sensor, cuz sometimes it could be bad without any CEL. but I have a feeling its the engine.

if you get the accessport, you can also raise the idle. Mines set to 950 now. Smooth like butter at all times. Even when switching between AC, power steering, headlights, radiator fans. It was OK at 850 prior, but it sometimes was lopey.

Its out of warranty.

Question: Why do you think its the engine?? I have no problem starting when engine is warm..

Also, engine idles fine when warm.... down to 750-850 range.

Does the Rx-8 use a duty cycle controlled valve (or a stepper motor) like on a lot of cars to bring in extra idle air, or is it all integrated into the drive-by-wire system?

Thats the kind of info I'm trying to find out..

I haven't seen an IAC motor on the intake anywhere, so I think it's in the drive by wire system. I could be wrong though.

I would suggest a compression test.
I'm guessing that one of the seals (side,apex) might at the in-spec out of spec tolerance. Don't forget that metal expands as it heats up. As it warms up it expands just enough to make a seal.

The idle is controlled by the PCM...using the drive by wire throttle opening as an idle up.....

I highly doubt its compression issues..

Just so I clear up some myth about rotaries... when you loose compression, its usually warm start not cold start. Also, maintaining low idles is near impossible with low compression engine. Hence I highly doubt is compression.. If I thought it was compression, I would of checked it myself as I have 1 x old school Mazda compression tester and 1 x newer Mazda OEM compression tester... But what I know about rotaries, its not it..

What I'm looking for is not how idle is controlled (I know that is the drive by wire is controlling the throttle) but what sensors it reads and how ECU is translating the read out. At this point, I'm very disappointed with the RX8 as My FDs get better gas and makes more power!! Also, Much easier to work with in comparison.

I have a similar issue. This started about three months ago: every morning during a cold start (but even when it's 60+ outside) the engine will idle very high at first, then when I release the clutch, it goes from about 2500 rpm down to 1200 or less, and continually goes back and forth, making the car sound like it's about to shut down. When I depress the clutch, the idle straightens out. I can also add some throttle and keep it steady. This all goes away as soon as the car is warm, and usually doesn't happen later in the day.

I took her to the dealer and they could not duplicate the problem, of course. So I'm stuck with it for now, and the warranty will be out in July.

ESS :eyetwitch

Please let me know if you get this sorted out... I'll do the same..

that's the throwout bearing.. unless there is a serious engine problem I doubt your car will shut down.

[QUOTE=arattle;2459794]I have a similar issue. This started about three months ago: every morning during a cold start (but even when it's 60+ outside) the engine will idle very high at first, then when I release the clutch, it goes from about 2500 rpm down to 1200 or less, and continually goes back and forth, making the car sound like it's about to shut down. When I depress the clutch, the idle straightens out. I can also add some throttle and keep it steady. This all goes away as soon as the car is warm, and usually doesn't happen later in the day.

there is nothing wrong with your car. and i wouldn't even mess with throttle or clutching to alter idle. its doing a fine job warming up... the coolant hose running thru the throttle body is warming up the air charge on warm-up.

besides, do you really want the rpms to be at 2500 when you have the clutch in??? what if you forgot its in gear and took off at that rpm??? think maybe its for a safety reason there that it does that?

anyway, its normal. and less annoying than the older iacv that gets dirty and clogged, and fluctuates when wrong cleaner is used and freeze up the valve...leading to just plugging up the sucker and low idle on start up.
so this is nothing to get worried over.

If you have or can download the shop manual, you'll see the step by step check down for this issue and what to troubleshoot at each step.

I had a CEL, though, for idle too low - can't remember what code that was now...mine would just die at idle and after a while just wouldn't start at all - but at WOT pulled strong as ever. After going through I discerned the throttle body had gone bad. New throttle body in place, everything back to normal.

Then to verify this was in fact the only issue we installed the bad tb on my friend's RX-8...his car wouldn't start either and had the same issues mine had before the new unit.

^ how much the cost to replace the TB? did you try clean it before? and lastly, i don't know the TB part number, is it same for AT and MT? anyway here's the link for the shop manual: https://www.rx8club.com/series-i-tech-garage-22/workshop-manual-120822/

[QUOTE=TrochoidMagic;2464663]
you neutral position switch is going..

beers :beer:

your idle on a no-mod car should be 820-830 rpm... even if it drops down from that, your engine should lift it to normal...

i had the same issues approaching 50K klm and the dealership just cleaned the throttle body ...and everything returned to normal!!! pretty much easy DIY job!!

[QUOTE=swoope;2465705]
Yes I think this is the case !

+1000

ousiastika I believe that someone can try to clear the throttle body just to eliminate the possibilities !

Claus How is your idle going now ? Do you have any issues or you forgot all about idle after the cleaning?

Did your dealer propose such a solution (clearing throttle body) in order to solve the idle problem or this was your idea?

my dealer proposed & i followed (watching him do it with a spray) !!! idling is xcellent now... no problems at all !!! ;-)

We did clean it, but it didn't help.

I'm not sure of the cost, as a friend has a wrecked RX-8 so I pulled the throttle body off of his.

thanks guys! I've now told by several that it could be the TB.

I'm going to take it out (I have to wait as my 7 and my 4Runner is need of work) and either replace it with the one I have or clean it!

Also, This morning, after trying to clean it couple of times, I noticed the drive by wire TB was making this humming noise... Wondering if this is normal or not. This was after trying to crank and after engine is shut down.