So for months my car was idling around 500-750. I thought it was my intake mods, k&n, etc.. for the life of me, I couldn't figure it out. I replaced Plugs, Wires, and Coils.. Cleaned engine with Seafoam. etc... I thought mabey my engine was a dud. I was afraid to bring it to mazda, because of my new headers, midpipe and exhaust, so I lived with it. Then it started to get worse, I'd stall when I pushed the clutch in while moving and coming to a stop. or It would idle so low, it would get ready to stall out until I was completely stopped and it would catch and go back to 750-800 rpm's.

well, I finally got fed up and ripped the whole intake apart and I found the problem! there was a really small hardened pool of oil right under the butterfly valve. I cleaned it up. put it all back together. and it idles so nice now, slowly coming back to 1000 and then down to 950-900 where it rests.

So, if you have any erratic idle problems, check your throttle body for oil buildup. I didn't even notice it last couple of times I had it apart. I just took some 800 grit sandpaper and throttle body cleaner to it..

 

glad you got it all fixed!

 

congrats on the fix, mine always idles under 1k rpms and my shift **** vibrates when it does that

 

I have an incredibly rough idle I havent been able to get rid of, Ill PM you to help me out bc Ive never taken it apart lol.

 

Check your motor mounts first if the idle is rough, if it is low then follow OP's post.

 

is it normal for the idle to be around 700-750ish? and is it also normal that when it idles around that range, the shifter vibrates to the point where i can see it vibrating maybe 2mm or 3mm side to side or back and forward. more of a rotating motion. but at 1000 after coming down from above that, the shifter vibes only a little then goes to 700 and vibes a lot. is that normal?

 

are you sure it was oil and not carbon?

 

mines idles one needle width above the 75o mark. and occasionaly sits on the 750 mark. is that normal?

 

Mine Start Vibrating When I Install The K&n Typhoon Intake,, Im Gonna Take It Apart This Weekend

 

nice fix

 

Its a basic throttle body cleaning service! spray with carburetor or throttle body cleaner and use a tooth brush around where the throttle plate touches. Don't think its a definite fix because the IAC(Idle air control Valve) could be sticking and cause the same issues. I have been doing this to my Honda for a while because I'm saving to get a new throttle body and IAC valve, I don't have an 8 yet but I am unsure if it has one so someone correct me if I'm wrong. If cleaning the throttle body works and it doesn't come back for a long time stick with that. When you seafoaming the engine do the throttle body together.

 

This is unfortunately a common problem: see this thread: https://www.rx8club.com/series-i-trouble-shooting-95/oil-inside-intake-box-148016/

You don't say your car's year, but if it's an '04 or early '05 the crankcase breather tube from just below the oil cap heads directly to the intake... All of the gunk that boils off after a cold start turns the intake tube into gooey varnish. gaah!

Mazda re-routed some of the plumbing on the '06's and later to make oil in the intake less of a problem.

A simple preventative solution is to install an oil / vapour catch can in this line. Greddy and others make expen$ive shiny solutions, but Kane suggests that you use an air-water separator for an air compressor to make your own catch can for ~$40. (thread here)

 

I need to look this stuff up, Ive done the same, replaced coils, plugs, wires, CAT!!! everything and my idle still dips to500 then back up to 800 then back to 500 then up to 800!! so annoying, done this since day #1