I usually set the cruise control at 65-70, so that means that rpms are closer to 3,750 or so.

 

Mine is also steady according to my Garmin GPS. I did see that my car speedo is off 1-2 mph, high. With cruise set at 74, the gps says 72-73.

 

Mine surges and shows on the speedometer (rocks back and forth between 69 and 70).

Level road, no wind, AT, about 1400 miles on the odometer.

Noticable surge that would be noticable on a long trip. Engaged the cruise control 2x so far and both times I could feel it for the whole session.

 

Katchoo, try at various speeds if it does it ALL the time. Mine does it at certain speeds and not at others. It is VERY annoying and they will have my car in the shop as soos as the stupid winter we have is calming down a bit. (no winter tires)

 

Since I first posted this thread, my situation has improved. The last two times I used my cruise control (set around 69 or 70) I did not notice any surging. F1michel, hopefully this happens with you as well.

 

i'm sure you will feel it again, depending on your speed . I will have them fix it even if it takes 15 trips.

 

My main drive is a weekly cruise of 300k and return, all on major highway, so I use the cruise control a lot. I find the surge consistently occurs when you hit resume at about 100kph in 6th, on an uphill section. That is around the magic 3250 rpm, which is very interesting.

I am just about to have my 20,000k service. I have spoken with the service people about the surge before, but no solution. I will raise the issue about the ports with them and see what they say.

IMO, the surge is enough to be potentially dangerous. I usually set cruise at 120kph; when the surge occurs, it will regularly take the car to 135kph and beyond although sometimes it will simply go to, say 125kph and the settle back. All this makes me think it is more ECU-related than anything else.

 

I have not noticed this at all, and I take mine on 200-300 mile round trips 2-3 times a week.

 

me either. used cruise at 66MPH in 6th gear on a 100 mile trek today. worked flawlessly.

 

AND

Have you tested as I suggested, ie, hit 'resume' at around 100kph (=60mph) on a slight uphill? I was doubtful, too, when this was first raised, but the problem is there.

 

I am a fairly new RX-8 owner and have this very same cruise control issue....slight back-forth speed surge. If I set the cruise right as the digital speedo moves to the next number and press set it is enough to get the speedo to change back-forth as well. My car has more than 2000 miles and the issue is still as noticeable as when I first bought the car. I am wondering if any solutions to this issue have been found. Thanks!

 

My cruise control is pretty steady. However, while browsing www.Mycarstats.com I found the following complaint listed:

CONSUMER COMPLAINT: ODI Case Number: 10135414

Component: VEHICLE SPEED CONTROL:CRUISE CONTROL

Details: DT: THE CONTACT OWNS A 2004 MAZDA RX8. THE CONTACT STATES THAT WHILE DRIVING WITH CRUISE CONTROL SET AND HITTING THE BRAKES TO SLOW DOWN OR STOP , AND IF PRESSING THE RESUME BUTTON ,THE CAR WILL ACTUALLY SET ITSELF 5 MPH MORE THAN WHAT ORIGINALLY HAD THE SPEED SET FOR. ONCE THE CAR GOES TO 5 MPH OVER THE SPEED THE CAR WAS SET FOR THE CAR WILL ACT AS IF IT WAS TRYING TO MAKE ITSELF GO BACK DOWN TO THE SPEED THAT WAS ORIGINALLY SET ,AND THE VEHICLE WILL JERK VIOLENTLY. THE CONTACT WAS TAKING THE VEHICLE TO THE DEALERSHIP ON THURSDAY TO SEE IF THEY COULD DIAGNOSE THE PROBLEM BECAUSE THIS HAS BEEN OCCURRING FOR A COUPLE OF MONTHS. THE ONLY WAY TO MAKE THIS PROBLEM STOP IS TO TURN OFF THE CRUISE CONTROL AND RESET IT AND THEN IT WILL STOP. THIS PROBLEM WITH THE VEHICLE AT HIGHWAY SPEEDS WILL HAPPEN AT ABOUT 60% OF THE TIME THAT THE CRUISE CONTROL IS SET. ALSO, THE ENGINE FAN WILL STAY ON ALL THE TIME. THE DEALERSHIP IS UNABLE TO DUPLICATE THE PROBLEM. THEREFORE , IT CANNOT BE FIXED AT THIS TIME. THE ELECTRIC FAN WILL ACTUALLY STAY ON WHILE THE VEHICLE IS TURNED OFF. THEN BY TURNING THE IGNITION BACK ON AND OFF IT THE VEHICLE WILL STOP RUNNING. THIS MOSTLY OCCURS IF THE VEHICLE IS DRIVEN FOR ABOUT 30 MINUTES. *AK

Mine has actually done this one time - and one time only. It's not a surging effect. Like the complaint says, it is a pretty violent on and off type thing. It was pretty weird when it happened, but I've never been able to replicate it.

 

Thanks for the feedback. Mine is also slight....nothing violent or what I would call jerking. I first noticed it after I was using the cruise on a longer drive....after a couple hours I started feeling like I was getting car-sick and did the same thing, laid my head against the head rest and noticed the slight rocking motion. Out of cuiosity I canceled the cruise and drove by foot and the surging stopped. After reading the comments about it being a possible rpm driven issue the next chance I had I sent the cruise in 6th, then tried at the same speed (approx 70mph) in 5th. Surge still there and more noticable so I tried the same speed in 4th and it was even more noticable so I tried the same thing at different speeds and could not find a speed (above 60mph) where the car traveled smoothly while on cruise. Please update the site as any news develops....I will do the same. Love the car but the cruise issue has me a little put-off.

Thanks!

 

from my observation, there is no changing in speed, it's just a vibration. The vibration happens once every 2 seconds. I always felt it when i cruise around 55-60 mph and it goes away once it hit 65 mph or above. my first thought, it was caused by the road surface. but after i drove it on any other highways, i felt the same thing. From what I think it's a mechanical design problem. it's some kind of constructive interference from moving parts of your car (driveshaft, wheel,etc), so you will only feel it at particular speed because the frequency is math with each other. this is kind of annoying and i thought there was something really bad with my car. when i went back home to my country last summer, i experience the same thing on the airplane. so i think it's normal unless the vibration is real bad (resonance interference).