My wife and I purchased a 2018 CX-9 grand touring around 6 weeks ago (car has ~1800 miles) and at a stop I notice the tach will swing between 500rpm and 750rpm at a stop. I don't feel the idle change in speed but I'm surprised I can see it change on the tach (most cars instrument clusters aren't that sensitive). Anyone else notice this? I guess I'm surprised the idle isn't more stable.
Thanks,
Alan
Bingo! Just started getting the surging effect at 1,000 rpm and only on very light throttle demand while the vehicle is downshifting. Yep, you called it!
I'm going to start doing some isolation road testing on this problem. This vehicle has always shifted very smoothly and this was not how it behaved before. This was also not how any of the other CX-9's that I test drove behaved before making my purchase. This is new behavior and it seems to have come on rather subtly. In addition, it now lugs down from 1st gear to Idle at or below 1,000 rpm. So, you fee a slight 'thump' in the transmission (very subtle) when coming to a full stop - but only intermittently. This is definitely not normal. If it were normal, this behavior/characteristic would have been present from day one and in all other CX-9s that I test drove prior. This new behavior just began when before all shifts were extremely smooth regardless of engine speed or transmission speed.
I'm thinking the problem might be in the new Torque Converter design, quite honestly. I hope I'm dead wrong. In fact, I'd be rather happy if I were wrong.
iSKYACTIV-Drive incorporates a new 80% lock-up ratio that extends engine rotation with transmission rotation (extended lock-up synchronization). This takes place low on the RPM band and that's what causes me to think there might be a problem in the torque converter transitions at lower RPMs - producing the "lurching" effect, "lugging" effect, "sputtering" effect, "throttling" effect, etc., as the engine speed gets closer to idle and the lock-up remains in effect. iSKYACTIV-Drive was Mazda's attempt at a sort of hybrid-transmission. One that yields the benefits of CVT, Auto and Manual transmissions. This was supposed to be a smoother shifting transmission as a direct result, as just one of its proclaimed benefits.
Again, I could be wrong and I hope that I am. But, the "Full Range Lock-Up Clutch" design could very well be the issue and the new multi-disc clutch could be the culprit - or something closely related (connected) to it.