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Being in neutral while moveing

G

graver555

Nov 6, 2012
89
1
Monticello IN
#1
So I have a saturn sl2. My question is when I put it in neutral, what does that mean? Is it a total disconnect from the wheels and the engine? I remember something about when you jack the front wheels off the ground it they will still spin from the engine in neutral.

The reason I ask is the other day I was in neutral to coast to a stop and the tachometer started bouncing between 8 and 15 hundred (idle is normally about 11-14 depending on the weather)

I have noticed this at least 3 times, twice while coasting to a stop on level ground (it evened out once I was below around 35mhp) and when I was coasting down and back up a hill where I had to turn and it didnt even out till I was at about 20 at the top.
 
#2
graver555 said:
So I have a saturn sl2. My question is when I put it in neutral, what does that mean? Is it a total disconnect from the wheels and the engine? I remember something about when you jack the front wheels off the ground it they will still spin from the engine in neutral.

The reason I ask is the other day I was in neutral to coast to a stop and the tachometer started bouncing between 8 and 15 hundred (idle is normally about 11-14 depending on the weather)

I have noticed this at least 3 times, twice while coasting to a stop on level ground (it evened out once I was below around 35mhp) and when I was coasting down and back up a hill where I had to turn and it didnt even out till I was at about 20 at the top.
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Unless you drive a stick shift(if you do disregard this part), you have very few reasons to have your car in neutral, Cruising to a stop isn't one of them and is actually illegal in some places.

As far as your problem, Bouncing RPMS could be a vacuum leak, bad IAC, bad TPS, dirty throttle body, etc. I suggest you go to google and see if there is a forum dedicated to that particular car. If not just google "saturn sl2 bouncing rpms.
 
#4
fdeck said:
On my Saturn, weird idle issues were typically symptomatic of the emission controls getting gunked up with oil. How much oil does your engine consume?
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Oddly enough for 219k it leaks little to no oil. And it dosnt have idle issues at a stand still or it appears most of the time below 30.

As for cruising to a stop being useless I would rather not argue over what does and does not save gas atm as thats not why I created this post. I have always wondered about the illegal part, as how would they prove that you did it??? :confused:

If my either of my sensors were bad wouldn't my engine light be on?
 
#8
This is scary to think about right now.

Can I ask why you are shifting an automatic into neutral to come to a stop?

To answer your first question, in layman's terms, the wheels are connected to the engine via the transmission. When you shift the transmission into neutral the wheels are no longer connected to the engine.

graver555 said:
I have always wondered about the illegal part, as how would they prove that you did it??? :confused:
Click to expand...

When you rear end someone because you couldn't get out of the way by stepping on the gas it won't really matter. It's your problem no matter what.
 
#10
graver555 said:
So I have a saturn sl2. My question is when I put it in neutral, what does that mean? Is it a total disconnect from the wheels and the engine? I remember something about when you jack the front wheels off the ground it they will still spin from the engine in neutral.

The reason I ask is the other day I was in neutral to coast to a stop and the tachometer started bouncing between 8 and 15 hundred (idle is normally about 11-14 depending on the weather)

I have noticed this at least 3 times, twice while coasting to a stop on level ground (it evened out once I was below around 35mhp) and when I was coasting down and back up a hill where I had to turn and it didnt even out till I was at about 20 at the top.
Click to expand...

Idle should be about 650 RPM, not 1100-1400. An injected engine has an IAC (Idle Air Control) that may "hunt" if the wheels are turning, but the measured vacuum and throttle position don't match the speed. It's not a "normal" set of readings from the sensors.

An automatic transmission has a torque converter, which needs to exceed a certain speed of rotation in order to build up enough pressure for one side to cause the other side to rotate. Both sides have vanes on the inner surface which cause the fluid to move and, since a fluid doesn't compress much, if at all, the side attached to the crankshaft will eventually force the half that's not, to rotate as if it was mechanically coupled. Once the engine speed drops below a certain point, it allows the converter to "stall", which means it no longer drives the shaft(s).
 
#11
Nice explanation of the basic workings of a torque converter.
I'd also add that more important than the lack of engine rpms (as far as why the car doesn't move in neutral) would be that generaly in nuetral there's no clutches applied in the trans. Or maybe just one in anticipation of what gear your going to choose next.
This would be for a modern fully electronic trans. And I'm not the worlds greatest tranny guy although I am forced to play one at work on occasion.
I do agree about cleaning the throttle body. Especialy at that milage.
 
#12
1958Bassman said:
Idle should be about 650 RPM, not 1100-1400. An injected engine has an IAC (Idle Air Control) that may "hunt" if the wheels are turning, but the measured vacuum and throttle position don't match the speed. It's not a "normal" set of readings from the sensors.

An automatic transmission has a torque converter, which needs to exceed a certain speed of rotation in order to build up enough pressure for one side to cause the other side to rotate. Both sides have vanes on the inner surface which cause the fluid to move and, since a fluid doesn't compress much, if at all, the side attached to the crankshaft will eventually force the half that's not, to rotate as if it was mechanically coupled. Once the engine speed drops below a certain point, it allows the converter to "stall", which means it no longer drives the shaft(s).
Click to expand...

I know engines should idle that low but I have never actually had a car that did. Closest I have seen is about 900 from my dads big roadmaster.

Could the wheelside of the torque converter act on the crankshaft?
 
#13
graver555 said:
Oddly enough for 219k it leaks little to no oil. And it dosnt have idle issues at a stand still or it appears most of the time below 30.
Click to expand...
Then you got one of the good ones, and I have no advice for you. My Saturn engine disintegrated at 70k miles, but as I understand it, there were good engines and bad engines.
 
#15
graver555 said:
Oddly enough for 219k it leaks little to no oil. And it dosnt have idle issues at a stand still or it appears most of the time below 30.

As for cruising to a stop being useless I would rather not argue over what does and does not save gas atm as thats not why I created this post. I have always wondered about the illegal part, as how would they prove that you did it??? :confused:

If my either of my sensors were bad wouldn't my engine light be on?
Click to expand...

You really aren't saving gas, it is just stupid.
 
#18
68Goldfish said:
I might be missing something but I can't see your doing anything wrong or stupid by coasting to a stop in nuetral other than maybe a little more wear on the brake pads and that's probably negligable.
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Especially in a car this size. And I have lifetime replacement pads so its just a bit of labor on my part a month earlier or something.

I was super phyched though. Over the weekend I got 40 mpg over 160 miles (almost all highway though). Thats a new record for me.
 
#20
carl h. said:
If you drive 40 mph you will really do better.
Try turning the car off when you are coasting for some real savings.
Inflate your tires to the max printed on the sidewall.
Click to expand...

Well I was on the interstate since I was in a hurry to get home from college for a weekend to see my gf....

This was the second time I've made a long distance trip on the interstate. Over the summer I made 36 on my way to work about 2/3 county roads.

Turning my car off is usually where I feel uncomfortable at. I figure i can throw it back into gear almost instantly in case I have an issue but not so much if the cars off.

Mayby next time I head home I will try backroads and have a hypermile contest with myself to see just how well I can do.

Biggest difference in milage was when i checked out my breaks and realized one of the pads was wedged in sideways grinding against the rotor haha.
 

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