2019 CX-9 Rough and High Idle 2.5L

2019 CX-9 Grand Touring AWD
About a week ago I noticed that when I would come to a stop at a stop sign I could feel the car downshift into 1st gear. It didn’t happen all the time but it was noticeable and a completely new feeling, like a subtle bump. Never felt that before since buying the car brand new.

Once I got home I put the car in park and left the engine running. My idle was bouncing between 750RPM and 2,000RPM. If I pressed the accelerator while in park it would increase as expected. I would take my foot off the accelerator and it would settle down to about 500-750RPM and start surging to approximately 2000RPM again. Turned the car off/on and it exhibited the same behavior.

Drove the car normally for a few days and today I noticed that the car, after driving for a bit, would idle really low below 500RPM, and I could feel the car shake and rumble slightly. This was while in Drive sitting at a red light. I thought it was going to sputter out and die on me in traffic.

Searching the forum for low or rough idle on the 2.5L has brought up a few scary threads mentioning engine or head replacement… So I wanted to post my details here to see what you all might think.

It’s a 2019 CX-9 AWD GT with only 14,000 miles and still under warranty until August 2022.
2019 CX-9 Grand Touring AWD
I wanted to update this post just in case anyone else has this issue and needs some direction.

I took the car into the dealer at the end of January. The car was "fixed" on February 1st. There was a code stored in the computer (P0507) which was pointing to a throttle body issue. The tech measured the resistance at the throttle body and it came back at 139 ohms. Standard range is 0.3 to 100 ohms so they replaced the throttle body.

I picked up the car and during the drive home the car was still showing the same symptoms. I bought the car back for another look but needed to wait for a loaner vehicle to be available. After a few days with the car they determined a hose wasn't completely put back on and was causing a vacuum leak.

I picked up the car again and it still showed symptoms on the drive home. I turned around right there and left the car with the dealership on March 8th. On Thursday the 17th I was told that they had to open a "hot line" call with Mazda corporate. The engineer on the phone was able to look at 10,000 miles worth of logs in the computer and told the local tech to replace the purge valve. I picked up the car and lo and behold the problem is gone.

In addition to fixing the issue the car feels like a completely different car. I was driving a CX5 as a loaner and I remarked to the dealership about how the CX5 was so much more responsive, quicker, and shifted like butter. My car was not like that. It's the same engine and yes the CX9 weighs more but the difference was significant. After getting my car back it feels a lot closer to the CX5 that I was driving than the way it felt since purchasing it new.

So there was definitely something that went wrong early on or was bad from the factory and I just didn't know it. All said I'm happy to have my car back.