truelove

my dealership just installed a new engine wiring harness last week, and ever since then my engine revs at idle. it's worst at a cold start when it'll rev from about 1000 rpm to about 1500 rpm. and it's not a gradual change either. it'll just rev right up to 1400 or 1500 rpm from 1000 and drop right back down. it does it when i've been driving a while too but not as bad and not all the time. it drives me nutz expecially when it decides it's gonna do it right when i'm trying to take off in 1st gear.

anyone have any problems like this or have any idea what causes it? i guess it's back to the dealership this week.

jpb5151

Yes, I'd take it straight back. Who knows, maybe they put in something defective, missed a wire, etc, and didn't test it enough to find out.

Outland

Sounds like a voltage problem in the TPS. But then again, MB's use a digital throttle, no linkage, so I don't know if these cars even have a TPS?

I think its obvious that the harness replacement is directly related. Take it back to the stealer.

truelove

oh, there's no question that it's going back to the dealer. i was just wondering what could cause it. i hope it doesn't die one me.

DCXdynodog

Interesting, I just took my car in for a number of issues - one being if I have the cruise on at 35 mph, de-clutch and go to neutral and coast - the engine drops to 1500 rpm then flares part throttle to 3500-4000 rpm. very reassuring

Now I can repeat this and I give the dealer a very detailed written description of how to make it happen so they can diagnose, repair and test the repair... so I get the car back and on the ride home from work it happens first try. Only now, it goes right to the redline very aggressively, they made it worse!
Gawd how I hate dealerships

I'm not a big fan of electronic throttle control to begin with, the lawyers are gonna love these someday.

Let's hear everyone's ETC horror stories, there must be more...

Jim Banville

I haven't driven a stick in a number of years, but let me get this straight... you're going 35mph in say, 3rd gear, with cruise on, at which time you push in the clutch, put the transmission into neutral, then release the clutch? Am I correct up to this point? I don't mean to sound rude, but I really don't understand why they even put cruise control in a car that can't shift itself, but anyway... why would you be using cruise while going 35mph, and why would you coast in neutral (especially with cruise engaged). I'm sure you have some unique experience where this all seems plausible. As I said, it's been a number of years since I drove a sick. I don't recall ever coasting in neutral. I only put my car in neutral while stopped. I was always either in gear or switching between gears while moving (as I recall). It just sounds like some rare scenario that is causing the logic circuitry to foul up, or I could be completely wrong

DCXdynodog

Doesn't matter why I drive this way. This should not happen, the clutch has a switch just like the brake to cut the cruise, in fact, MB saw fit to let us upshift and downshift and it resumes the cruise for us (within a 4 sec timer on the clutch cutoff) . In my case it's a very handy feature.

Yes I have found a flaw in the MB control unit or software and it needs to be fixed pronto. This and Truelove,s experience show this electronic throttle can be dangerous.

Did not happen in 10 years of driving a $12,000 Honda.

dswildfire

i'd dont like the electronic throttle, it seems rather non-linear to me and the whole adaptive throttle bit bothers me, because some days i'm mellow and light and the pedal, and other day's i'm wearing cement boots. i mean it's nice and all for modulating speed during normal driving, but i'd rather have that throttle cable back.

truelove

well, i called the dealership and they said they've never dealt with a problem like this before (they're a small dealership). so that makes me think that they're probably not gonna get it fixed right the first time, or even the second time. this could be an ongoing thing so i'm preparing myself for the worst.

but don't get me wrong. i like my dealership. they're always very very nice and treat every problem (even the most minor) very seriously and they make sure i'm happy before i walk out the door everytime.

MarkL

It's true that there's a timer on the clutch cutoff, but, if you quickly engage the clutch and shift to neutral, the timer is not in the loop. Although shifting w/ the cruise on seems fine, I think I'd agree w/ Jim about going into neutral -- what part of the cruise control system do you think would detect this? The system probably keeps accelerating because it can't figure out why the car isn't going the set speed. I had a VW Passat before my 6-spd C240, and I remember an issue that if you had the cruise on in neutral, it would rev up to the redline pronto -- and that didn't have an electronic throttle...

QED: Being in neutral with the cruise on is probably not a good idea!

MarkL

I'm sure they treat you well, but after a time, you'll get frustrated w/ the level of service if they can't fix things right the 1st time no matter how nice they are... I've been lucky so far, but I would dread taking the car in for anything other than normal maintenance.

BTW, over the weekend I filled up the tank and my gauge didn't register "full". I'm hoping this was just a fluke that somehow I didn't fill up all the way, but we'll see...

jpb5151

Never had that happen, but after reading some of the fuel gauge posts I started counting the gallons just in case. Hope it turns out OK for you.

avlis

I may be miss understanding this whole thing but here's my idea...

Though I've never tried shifting with CC enabled I relize it can be done. I'd expect the compter to let off the throttle for the de-clutch then, after a few seconds, get back on the throttle to resume the set CC speed. At this point the computer EXPECTS the car to be in gear. It doesn't expect a driver to miss the shift or leave the trans in neutral. It just keeps giving throttle to get car up the set speed (still thinking it's in gear). This seems normal to me, am I missing something?

mctwin2kman

Why in god's name would you have the cruise set and the car in nuetral? Second the darn Germans that allow cruise to be set under 45 MPH are just morons, there is not need for cruise control at that speed. The computer does not know what gear the vehicle is in or if it is in nuetral on a standard shict car. Standard shift vehicles do not have nuetral sensors on them. So after the four second time is up the computer is going to give gas and plenty of it to get the car back to cruise speed, but when in nuetral this will obviously never happen. I wish the cruise would work the same as it does in Europe where you set a limit and floor it and it goes no faster. Instead of the lazy way us Americans use. Then we would not have this problem would we.

DCXdynodog

Wrong , wrong and wrong again.

You should go to Europe where you would be happy...
then you would not have this problem would you...
of course there's a good chance you would be unemployed there and have no need for a car at all.

DCXdynodog

I think it knows if it's in gear, these circumstances are the only set so far that this happens. So far any other time I push the clutch in and toss it into neutral it shuts down and stays that way.

mctwin2kman

Well, I got that info about the MB cruise in Europe off this site so I have no idea what you are talking about, second in New York state it is frowned upon to use the cruise under 45 MPH and I assume other states also don't like it. In NYS I know Technicians that have wrecked customers cars setting the cruise whil in the city, of course most Chrysler vehicles will not set under 40-45 MPH so this is not good for the tech doing 45 with the cruise on in a 30. Second cruise is intended for highway use, I know no one lazy enough except you of course to drive through the city with cruise engaged. That is my opinion of course and you are of course entitled to yours. I used to have some respect for you knowledge of vehicles but lately I have seen that slip so. To comment on my Europe comment instead of the one that states the car computer has no clue what gear I am in was justr darn silly. Just ignore the rest of the post and read the first few lines like every other person, this is what is wrong with the American Public today. To many people just ignore the whole statement and focus on the first part. This is a discussion so I would assume to have one people should read the whole post and then comment on the whole post. And yes I think any manufacturer that allows something like the automatic control of the throttle to be able to be engaged at such a low speed.

No to mention that for a tech you should know it would be pointless to have cruise engaged and the car in nuetral. My wife even would know that and this is her first manual shift vehicle. There obviously is no true nuetral sensor in a standard shift tranny or remote starter manufacturers would use it for there starters on manual cars.

DCXdynodog

If the cruise was intended for highway use only it would not work at lower speeds.

If there is no neutral sensor in this car, how come the cruise shuts down every time I test it by putting it in neutral at other speeds, loads etc. ?? How come the service manager is on the phone with MB directly trying to figure this one out? How come he thinks something is wrong??

Not that you deserve to know, but...I work the afternoon shift and there just isn't a whole lotta traffic when I drive home, but there are lots-o-cops out doin' thier job and I have long stretches through the city.

I like to relax a bit on the way home and you need to think a bit more.

mctwin2kman

Mine is an 2003 and the cruise only delays a second or two when put in nuetral and revs after that. This does not need a nuetral switch but a clutch switch, which we know the car has because we need to push the clutch in to start. DCX, you are just making yourself sound more clueless, as you should know there is a clutch switch and no nuetral safety switch on a standard shift vehicle, unless it has all changed with Getrag in the last 7 years since I worked on vehicles. I would have thought you would have realized that the sensor or switch in on the clutch and not on the tranny itself. Go to How Stuff Works and search for the Manual Transmission and read it and you would realize there are way to many places that would need a switch in order to know what gear you are in, especially in a 6 speed.

mctwin2kman

Update: I just tested mine and it does rev up to attempt to hold the cruise speed after a shift to nuetral. I would assume this is because the car computer still has the cruise set and assumes the driver would have shifted into a gear not nuetral. Although I am still trying to mentally figure out why anyone would shift to nuetral with the cruise set anyway, I am at a loss on how to explain this any further. Cruise used to cancel when the clutch was depressed on other vehicles as I verified this with a man who has driven far more standard shift vehicles than I and for far longer than I. He is a few years older, like 25, so I would believe him on this one. But for validation of this so called problem, I do not think this is an issue since no one should be driving in nuetral with the cruise on anyhow, that it happens in my vehicle as well. Am I going to rush to the dealer for a fix? No, because it is working as it should.

neptunespeed

Being the dork that I am, I tested this too. Same thing happens in my car(2003 C230 sedan). Just wanted to see if it was an isolated problem. But I've never put it into neutral during cruise before and won't again.

mdp c230k

It's normal as they say, the car is trying to maintain speed and does not know its in neutral. Ain't broke, don't fix.

mctwin2kman

That is what I was trying to say all along, so thank you for your input as well....

20FHK02

Out of curiosity, here are what I just did during my lunch trip. Vehicle test was a 02 Coupe 6-speed:

Case 1
Set cruise at 70mph at 5th gear, maintain speed for 10 sec and then shift to 6th gear. Results: Speed retained as well as cruise.

Case 2
Set cruise at 70mph at 5th gear, maintin speed for 10 sec and then shift to neutral. Results: RPM started to drop after 1 sec and speed started to drop after about 2 sec. But no over revving occured.

Shift back to 5th gear, speed continues to drop -> cruise was cut.

Conclusion
Maybe there is another cost cutting measure on the 03 models. On my 02 model, there is indeed a neutral sensor and my car did not over-rev.

mctwin2kman

Unless there have been some severe transmission enhancements in the last few years there is no way to see nuetral on a standard shift tranny. There are no sensors to tell you the gear and last I saw the only sensor in the darn things may be a fluid sensor, but I have not seen them either. This is why a standard shift tranny is so much less money, there is no advanced tech in one. GO read how stuff works and you will see that there is not a whole lot to a tranny. In the old days the clutch killed the cruise so maybe it is a fluke that our cars even hold the cruise when the clutch is depressed. There should never be a need to shift with the cruise set, as you shoudl be cruising. There are no advanced electronic sensors on our trannies. They are just a plain jane Getrag transmission.