I've had this car for about 3 months now. It has approx 83K miles and I've started to notice that when the engine is under load (drive or reverse) the idle is rough. It bounces around from 750 to 1000 RPM and when i turn the A/C on the air it blows out goes from very cold when the RPMs go up to not so cold when i'm at a traffic light for example.

I bought the car from a guy who had it sitting in his garage for 4 years after he had hit a cub and completely f*ked the rear passengers side suspension. He supposedly had the engine replaced under warranty so the engine had only about 5000 miles when he stored it in his garage. I replaced all the parts and before i got it back out on the road i replaced all fluids, recharged the A/C, new battery, new coils, and a new radiator because it was leaky.

So what could cause the rough Idle and A/C temp fluctuations? Could it be that the engine is dying or some other thing? Do you guys recommend i get a compression test or do one myself? and how would i go about checking weather the previous owner did have the engine replaced? or if its just B.S?


Edit: heres a video of almost exactly how my car idles.

 

If you wanna know if your motor was replaced, call mazda, any dealership with your vin number. They will be able to tell you whatever has been done to your car. Whether it be scheduled or unscheduled maintanence. New coils? What about plugs and wires.

 

do you have any form of cold air intake? if so be sure the screen is still in the intake in front of the MAF and only a few inches up the pipe, if not this will cause a rough idle and surge. mine turned sideways and exhibited those symptoms.

you should also check your coolant level since the light is on which could contribute to your A/C issues(if it's not a faulty sensor).

 

Karack, he said that was a vid of the same symptoms he has. So not a vid of his in particular.

 

Yea that video isn't of my car. I do have a K&N intake but i want to go back to OEM. As for plugs and wires, i did not replace but will once i replace my brake pads and rotors.

 

Just called my local Mazda service center and confirmed that the engine was replaced back in 2010. with that out of the way i'm pretty sure its not engine failure so i will replace the plugs and wires soon, hopefully that fixes my problem.

 

Eddy that is probably going to fix your problem. Plugs and wire's have a life expectancy just like the coils. Honestly though, i would go through your motor and check all of your grounding points for the motor. Make sure your good. Specifically their is one located on the LEFT side of the engine bay around the upper manifold. Im a little busy to find n post a pic. But mine has come undone twice over the course of 3 engines. Thats WITH threadlocker. I dont understand it. I was starting to think gremlins were afoot. BUT hasent happened to me in over a year and a half now. A rough idle problem can also be caused by motor mounts SSV, MAF. Many many things. so lets try this n see where it goes. If it fixes the issue we will move onto the a/c

 

i would still check that the screen is installed upstream of the AFM, people do stupid things when they modify their cars and think they know better.

 

You calling me stupid? jk i checked it and its fine. although i did remember that the previous owner installed a voltage stabilizer would that affect idle in any way?

 

Check your motor mounts…I would also clean the MAF and ESS. Get rid of the k&n intake as well

 

Was washing my car today and decided to look under the hood. I took off my K&N filter and cleaned it with the solution along with re-oiling it, then i took off the intake tube, removed and cleaned the throttle body with a rag and paint thinner by wiping off all the carbon buildup. This seemed to stop the bouncing from 750 to 1000 rmp and is idling just fine now. I am still going to invest in new plugs + wires as soon as i get my paycheck $$$$

 

It seems like most idle RPM fluctuations are related to the intake more than engine compression. Our MAFs are really sensitive and even the slightest variation in air flow can cause these issues to happen. Glad you got it fixed, by any chance did your throttle body have any signs of oil? Most likely, the rough idle was caused by oil blowback which contaminated the MAF and throttle body. I would install an oil catch can while you're at it.

Posted From RX8Club.com Android App

 

There was oil on the MAF but it was from the K&N filter, they require an oil to be sprayed onto them after you wash them, i remember going spray happy with the oil which lead to the excess oil being sucked into the intake.

Could you point me to a DIY on how to install a oil catch because as most of us know the search feature here kinda sucks

 

https://www.rx8club.com/series-i-do-...-basic-164463/

That took less than 15 seconds to find. Use google. Type in RX8 Oil catch can DIY. Bam- rx8 club forum.

 

Thanks.

 

if you are replacing wires and plugs, what about the coils ? If they are oem and have 30,000 miles on them, they need to be replaced. Replacing worn out wires and plugs without changing the worn out coils would be a total waste.

 

I replaced them prior to replacing the plugs and wires. they have less than 1000 miles on them

 

Since you live in Albuquerque, you may want to run a hotter plug due to altitude.