This topic has been posted before but the last post was dated in September and I'd like to get some updates re: the cruise control surge.

Like many RX-8 owners, my car is doing the same thing. I set the cruise for 65-70 and I can feel the car rocking back and forth even though the difference in speed does not register on the tach or speedo. It is subtle but definitely noticeable.

My car has just >3,000 miles on it, though I don't use cruise control very often.

Your experience?

Mine seems very consistant. I am going on a 300 mile trip tomorrow so I will take my garmin gps and check it out.

Mine doesn't surge or rock or anything. Doesn't even skip a beat when I engage the cruise.. it just keeps on without any change in speed.

However I do have that stupid false check oil light at speed.. need to get that oilpan replaced... I just don't want anybody else touching the car but me!

Yah. so with my 3000+ miles I have zero surging.

I dont have that issue either. I dont think it's that many owners that are seeing this at all. When it first came up I tested CC at speeds from 65 to 80MPH and didnt get anything at any speed.

No cruise control problems here and used it extensively on my 2000 mile round trip to VA for Christmas.

The original issue stemmed from when you release the cruise control and press reset (typically on an uphill angle) from a slower speed (15-20mph), some people, including me, have experienced the cruise going WELL beyond the original setting, only to fall back to normal after a seemingly long time above the original setting.

It is intermittent, but is annoying in traffic when it does happen.

No problems with the cruise control here either, and I love the way the speedometer shows and stays on the EXACT mph. I am spoiled by the speedo, my next car will have to have a digital speedometer.

Mine also worked just fine and I went on a 2,900 mile trip for the holidays. My cruise control was active for about 1/3 of the time.

I had the surging problem once, but it was only after I had slowed for a moment, then hit the resume button.

Are you sure you aren't just feeling it pull now and then as the terrain changes. I can't imagine a scenerio where the speedo and tach wouldn't register a speed change.

I haven't noticed a cruise surge either. AT or MT?

Originally posted by tpryor
The original issue stemmed from when you release the cruise control and press reset (typically on an uphill angle) from a slower speed I don't think I would use reset on an upgrade. I use it in level cruising with no traffic impediments, but otherwise just come to the speed you want and click Set. Don't know why; I guess I don't like the acceleration rate you get when you use Reset.

That said, my cruise is rock solid. Speedo don't flicker like some have mentioned; click up or down in 1 mph increments; I am very satisfied.

Here is the original thread i spoke of:

http://www.rx8club.com/showthread.php?s=&threadid=10032

Definitely check it out so I can prove I'm not crazy!!!!:(

No problem with mine- in fact I've never had a car with CC that was so rock solid. And I love the cool feature of adding exactly 1 mph by tapping ACCEL and slow 1 mph by tapping COAST.

My cruise control has been rock steady.

Had mine since Halloween and have had no problems. Always smooth.

ok having read this thread and the previous thread from the link i have an idea- what if it is not surging at a specific speed but at a specific rpm range? perhaps the speed your setting it at is right about where the secondary or tertiary ports open. as the car moves up and down the rpm range slightly going up hills or downhills the port is open and closing. even slight grades might cause it to fluctuate enough to make this happen. what do you think?

My first 8 (VIN 883) did it once when going up a long grade. I don't remember what I did to start it surging but it was going nuts until I turned the cruise off.

Both cars oscillate when cruising on a slight grade but most of the time it's not enough to make the speedo change.

Vince

Not sure if this helps but what about the gas?
It got to 15 degrees here last week and mine would not idle at start up until it warmed up for a few minutes. Dealer told me to stop putting premium gas in it and just put regular. I changed gas and it started idling again. He said they have the same problems with high end VW's.

Ok, i have the exact same problem with my car since day 1 . (august 5th) I took it in twice for various reasons other then that and menrionned it both times. 1st time they di nothing,(i knew more about the car then they did at the time) 2nd time they said the had to reprogram it and that it should be fine... to no avail, it's still doing it, not ALL the time but at about 110 KPH it's very frequent, above 115 kph it almost never happens. i'm barely using the car for the winter but i will keep on bugging them with that problem until it is fixed !!

what is the rpm, roughly, at 110kph in 6th gear?

Originally posted by zoom44
what is the rpm, roughly, at 110kph in 6th gear?

I would estimate around 3350-3400... at least on mine (I have been making a conscious effort this week to use 6th gear on my way to work on a 55mph road to see if gas mileage is better under the magic 3250rpm point... I can go about 63mph and stay under there).

-Sean

that is pretty close to the 3250 point. i think this adds some weight to my arguement of the opening/closing port as a cause of the surge feeling.

Originally posted by zoom44
that is pretty close to the 3250 point. i think this adds some weight to my arguement of the opening/closing port as a cause of the surge feeling.

I'll bet you're right... add in the fact that my speedo is 5% off due to 40 profile snowtires, and that would put the magic speed at approx 109.5km/h<=>3250rpm based on my car and crappy math skills.

-Sean

Originally posted by G8rboy
...and crappy math skills.

-Sean

take note i didn't even try to do the math i wqaited for someone else to do it ;)

When my car was new and I would use the cruise control I never noticed any surging while holding one speed. However when I would change speed using the cruise buttons it would be very jerky. After a while the car smoothed out and now when I change speeds its very smooth.

The original post said he didn' t use cruize very much so I wonder if the ECU has to learn how to control the cruize control much like it has to learn how you drive. Just a thought. Try and use it a lot for a while and see if that helps.

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.

Originally posted by fxdsconv2000
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.

Originally posted by fxdsconv2000
I have not noticed this at all, and I take mine on 200-300 mile round trips 2-3 times a week.

AND

Originally posted by RX-GR8
me either. used cruise at 66MPH in 6th gear on a 100 mile trek today. worked flawlessly.

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. :confused:

I set the cruise for 65-70 and I can feel the car rocking back and forth even though the difference in speed does not register on the tach or speedo. It is subtle but definitely noticeable.

I found the same thing on my ~300 mile drive-home with my brand-new 2004. I had been set at about ~67mph for a while and gradually noticed a distinct rocking. I tried resting my head back against the headrest of the seat, but the motion was pronounced enough to lift my head forward even though I did not see the speedometer changing.

The problem occurred every once in a while, but never the violent changes described by Chasvhill's post and the cruise never changed my setpoint or failed to respect my setpoint, it just oscillated in a slight, but quite noticable way (enough that I knew passengers would remark on it).

Zoom may be dead on about the ports - statistically, it would be unlikely to get exactly that rpm range so not too common of a problem.

The only new information I can add is that for me the oscillations seemed to slowly get worse, then my cat was clogging up from day 1 and was replaced by my 4th week of ownership. I haven't had much chance to look for this oscillation with the new cat (hopefully the bodyshop who has been repairing my deer-damaged RX-8 for the past 3 weeks hasn't flooded the car 10 times and killed the new cat). Once I have my car back I'll hunt for oscillations during the two-hour trip home from the dealer.

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).