Rough idle, fine above 2500rpm?
 

Hi all

After having bad emissions which didnt pass i got the intakes to the engine replace which solved my problem with bad emissions above 2500rpms. The car however has bad emissions at idle and the idle is running really rough, the idle goes between 600 and 750 RPMs and the car shudders abit. Do i have an engine problem or might it be something else?. plugs leads etc have been recently changed as well as the battery. The car sometimes stalls at intersections and red lights as well.

Am grateful for any tips i can get

Moving to Troubleshooting.


I'd suspect a vacuum leak first.

Vacuum leak can cause rough idle, generally increases emisisons, and usually becomes less and less impactful the higher the air flow through the engine, as the leak is still a fixed amount of air. Say it's a 1 gram per second of air at idle, that is ~20% of the total air the engine is using, but at full throttle and ~8,500 rpm, it's about 0.5% of the airflow in the engine.

Where do i find the vacuumthingy then? would like to test if there is one or not

evap leak test. a machine fills the intake with smoke. this is how i found two vac leaks in my car but i think i still have another

you can also do it the redneck way. Grab your favorite cigar (not cigarette), disconnect a vac line, and blow smoke into the line. Leaks will quickly show up through escaping smoke lol. And no i am not joking.

Good tip, at least it sounds like it!! I will have to try this as I think I may have a leak also.

Which are the vacuum lines?

Here is a video of the car and its problems

Mazda RX-8 Issues - YouTube

https://www.rx8club.com/attachments/...-locations-jpg

there is actually a youtube video out there that shows this technique ... i am at work so i cannot find the link.

Sounds like you said plugs and wires were replaced. How about coils? Mine was never really that rough but some new coils cleared things up a lot.