Just got over 1200 miles on my car this weekend on a long trip over to Seattle. Finally got to use the cruise control and noticed a problem. On long downhill runs the car tends to surge. Meaning it kind of speeds up a little then suddenly slows then speeds up again. It cycles every 5 seconds or so and got to be really annoying. I ended up turning the cruise off on long hills and just controlling it manually.

Anyone else experienced this? I looked at the TSB's but couldn't find anything like it.

 

hmmmm that sounds wierd but i will give it a try tommarow and see if i notice that 2.

 

Sorry, no hills in FL to test this out on.

 

yes, mine does, too. 6mt coupe, long downhills (or short, too), surges back and forth. sort of holds speed, but not smoothly. haven't been to dealer yet. don't know if there's a fix. if you find out first by verbal or taking it in, please either post it as a follow up to your original, or pm me. thanks. i'll do the same if i hear of something or get to the dealer.

BONDg35c

 

The hill may be too steep for the car to maintain the speed you want. Try downshifting one gear. (Kick it over to 4M for an auto.) That should give the car a little more friction to deal with to maintain the proper speed.

2003.5 G35 Sedan Desert Platinum/Graphite Premium/Sport/Aero/Nav/Winter

 

I felt what I thought were the brakes being periodically activated by the cruise control on downhills to maintain speed. It was in 6th gear at about 70MPH. That might be what you're noticing.

 

The standard cruise control only regulates the throttle and not the brakes. Some cars equipped with the “laser or radar guide cruise control” can regulate both the throttle and brakes.

 

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I felt what I thought were the brakes being periodically activated by the cruise control on downhills to maintain speed. It was in 6th gear at about 70MPH. That might be what you're noticing.

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FD is right... the cruise control does not have any control over the brakes. No, what you're feeling is the torque of the engine pulling when the cruise control lets off the gas to keep the speed down, not the brakes.
I've noticed this with my coupe too, but to be fair, I've noticed it on every cruise controlled vehicle I've ever owned. I doubt there's a cure, other than perhaps using a lower gear as Ryoken suggested. On an incline, or on level surfaces the CC is smooth as silk, but on steep declines it's tough for it to regulate the throttle accurately enough to keep the speed even. I suspect it's got something to do with the computer's reaction time, or response speed... a human being can feather the throttle very slowly to maintain a constant speed, but the computer reacts much more quickly, leading to the "surges" you've experienced. Once it starts going over the set speed it just cuts out, rather than feathering off like a person would.

2003 G35 Coupe 6MT Leather
Premium, Aero
"There is no spoon"

 

Conquie, agree with you on most, but not all. Had 5AT in Lex before 6MT G Coupe. Now that I think about it, the cruise control (CC) never had a problem on any hill in the 5AT---completely smooth and seamless reduction in speed. But, logic tells me the computer was probably able to control both the engine speed (rpms) and the auto trans to some extent.

Compared to the 6MT, when it's in 6th gear, it's at a relatively low gearing with little stress on the engine (read: no way to employ engine torque to slow down the car/engine rpms) and no way for the computer or CC to control/change the gearing. Altho I have to say also that in my 6MT 'Vette of years back I don't remember the same issues of not maintaining speed on downhills in CC and top gear. Then again, in that car I hardly ever used the CC and that might be the issue!

I repeat: if anyone talks to dealer or whomever about it and gets some kind of answer, plz post for us (me) who don't have an answer. Otherwise, drive on and enjoy!

BONDg35c

 

Conquie,
I have had a few other cars in the past that had cruise control and I never felt such an abrupt change in throttle on downhill decents. I aggree that downshifting to fifth would increase engine braking and make it easier for the speed to be controlled by the throttle. The funny thing is, that if I turn off the cruise, I don't have any problem controlling the speed manually.
I suspect that the speed tolerance band is very small, only allowing +/- less than 1 mph variation, which causes the computer to adjust the throttle more often. If the tolerance were higher I would suspect that the throttle adjustments would be less noticable.
Whatever the reason, I would hope that with a minor software update this could be improved by Infiniti. I live a couple hundred miles from the nearest dealership so I don't know when I'll be able to get in to have it checked out. I will put it on the list of little annoyances (like the narrow seats that dig into my wide a$$) and have as many things fixed as I can when I make my next trek to the dealer.

 

hmm, have not noticed surges, but i have noticed the cruise control to be somewhat off, within 1-2 mph whenever going thru an underpass... basically its not as accurate as i would like it to be.

On the same topic of cruise control...each "click" of the cruise control will vary the speed by 2kmph, NOT 1mph as expected.
For example, lets say you are cruising at 75mph and want to decelate to 70mph, in most cars you would "click" the button DOWN 5 times. After a few seconds, the car will be going 70mph... NOT in the G...the cruise is set to decelerate/accelerate 2kmph for every push. So to go from 75 to 70, you'd have to "click" about 4 times, but this will get you to about 69mph (because of 2km = 1.2 miles).. just an fyi for those who havent noticed this.

<font color=green>-Rambo</font color=green>
G35c 6MT DG/Willow/HyperGround/BorlaExhaust<P ID="edit"><FONT class="small"><EM>Edited by ramborami on 08/06/03 11:57 AM.</EM></FONT></P>

 

Are you running the A/C in "auto econ" mode?

This use to be a big problem with older, inefficient A/C compressors when manufacturers had to figure out a way to improve gas mileage. The A/C compressor was such a monsterous cause of parasitic loss of HP that manufacturers added an electro/mechanical clutch to the compressor pulley. When this clutch cycled on, the car would slow down. When it cycled off, the car would speed up. You could notice it on my father's '68 Delta88 with the 455cid/4bll and my mother's '72 Buick LeSabre with the same drivetrain.

I don't know if the "auto econ" mode of our A/C cycles the compressor on/off. Anyone know?

I've never owned an MT with cruise control but I've always wondered how a cruise control could maintain speed on hills when it can't change gears. It would have to have serious power or be a very light weight car. I had an '88 Bronco (full sized) with a 302cid V8 that was seriously underpowered and shifted constantly on the gentle hills of the Piedmont of NC.