240 General: High Idle Only In N & P

[Moomoo]

It’s no help but I always expect my revs to go up when I slip my’91, 2.0l , 240 out of D into neutral. It never makes any perceptible change! 130k miles, new ATF.

Andrew.

[TheHungriestBadger]

Engine idle speed compensation for automatic tran OK 1-2-4 (depress the brake pedal, move the selector to D and then to N.)

The above is taken from the volvoclub FAQ page. I can confirm my diagnostics box says that it's okay (probably a good thing)... Unless it's an intermittent thing? Hey I'd rather live in blissful ignorance

Also dumped 1/4 can of carb cleaner through the IAC and shook vigorously multiple times and that didn't fix it. Unless someone has some magical cure, I'm content to call it 'normal' and just live with it. It's not doing any real damage except perhaps putting marginal levels of strain when going D -> N -> R or vice versa.

On a sidenote, does anyone know if it's detrimental to sit in D whilst stationary?

[Moomoo]

Originally Posted by TheHungriestBadger

The above is taken from the volvoclub FAQ page. I can confirm my diagnostics box says that it's okay (probably a good thing)... Unless it's an intermittent thing? Hey I'd rather live in blissful ignorance

Also dumped 1/4 can of carb cleaner through the IAC and shook vigorously multiple times and that didn't fix it. Unless someone has some magical cure, I'm content to call it 'normal' and just live with it. It's not doing any real damage except perhaps putting marginal levels of strain when going D -> N -> R or vice versa.

On a sidenote, does anyone know if it's detrimental to sit in D whilst stationary?

The last bit; I was always told to slip into neutral if it’s going to be over a minute or so. Traffic lights etc.👍

[TheHungriestBadger]

Appreciate the advice, a quick look through a StackExchange (generally good forum) has plenty of views both ways. Cobbling them together, it appears as though:

1) Leaving in D creates extra drag (as previously stated in this thread). This means the engine would idle low. To compensate, ECU modulates the IAC which means more air, more fuel, more power/energy. This excess energy culminates as heat in the ATF. Too much of that would indeed be bad.
2) Leaving in N would therefore result in less drag = slight fuel savings at idle at the expense of wearing out shifter bushings etc. Apparently, it also allows one of the clutches to slip slightly, theoretically resulting in more wear. I guess this is why people say NOT to rev in N/P. This is especially pertinent in the ZF autos which apparently don't leave the ATF pump running when in N/P. The ATF pump on the AW7x does continue to run in N/P, thus it's not as much of a problem (although maybe don't make it a regular thing).
3) Something about the AW55 (basically a non-overdrive AW7x, right?) automatically selecting and deselecting N when at a standstill AND in D AND with foot on the brake... Will have to look out for that on my commute tomorrow. Allegedly this kicks in after 2 seconds, and kicks out again when the brakes are released?

Here's the link to that thread if anyone is interested:
https://mechanics.stackexchange.com/...c-transmission

[Othen]

Originally Posted by TheHungriestBadger

Appreciate the advice, a quick look through a StackExchange (generally good forum) has plenty of views both ways. Cobbling them together, it appears as though:

1) Leaving in D creates extra drag (as previously stated in this thread). This means the engine would idle low. To compensate, ECU modulates the IAC which means more air, more fuel, more power/energy. This excess energy culminates as heat in the ATF. Too much of that would indeed be bad.
2) Leaving in N would therefore result in less drag = slight fuel savings at idle at the expense of wearing out shifter bushings etc. Apparently, it also allows one of the clutches to slip slightly, theoretically resulting in more wear. I guess this is why people say NOT to rev in N/P. This is especially pertinent in the ZF autos which apparently don't leave the ATF pump running when in N/P. The ATF pump on the AW7x does continue to run in N/P, thus it's not as much of a problem (although maybe don't make it a regular thing).
3) Something about the AW55 (basically a non-overdrive AW7x, right?) automatically selecting and deselecting N when at a standstill AND in D AND with foot on the brake... Will have to look out for that on my commute tomorrow. Allegedly this kicks in after 2 seconds, and kicks out again when the brakes are released?

Here's the link to that thread if anyone is interested:
https://mechanics.stackexchange.com/...c-transmission

I don't think the BW55 (same as AW55) automatically changes out of D and into N if left to its own devices - it is a very simple machine indeed.

In the RB (244 with a BW55 transmission) I always put the motor car into N and apply the handbrake when I come to a halt. The engine speed rises by about 200 RPM as a result (there is no ECU to tell it to do anything else on a 1980 motor car).

:-)

[john.wigley]

Originally Posted by Othen

I don't think the BW55 (same as AW55) automatically changes out of D and into N if left to its own devices - it is a very simple machine indeed.

In the RB (244 with a BW55 transmission) I always put the motor car into N and apply the handbrake when I come to a halt. The engine speed rises by about 200 RPM as a result (there is no ECU to tell it to do anything else on a 1980 motor car).

:-)

That is so and normal behaviour, Alan. There is nothing 'wrong' about slipping into N at every stop, no matter how brief, but it does negate slightly the point of an automatic. I'm more inclined to agree with 'Moomoo', and do so only on longer stops, where it is also necessary to keep the engine on - e.g. when on a motorway.

But that is more to do with the driver's preference than the car.

An exception to the above is when driving at night, when I do slip it into N if there is someone behind me to avoid dazzling them unnecessarially with my brake lights.

Regards, John.

[Othen]

Originally Posted by john.wigley

That is so and normal behaviour, Alan. There is nothing 'wrong' about slipping into N at every stop, no matter how brief, but it does negate slightly the point of an automatic. I'm more inclined to agree with 'Moomoo', and do so only on longer stops, where it is also necessary to keep the engine on - e.g. when on a motorway.

But that is more to do with the driver's preference than the car.

An exception to the above is when driving at night, when I do slip it into N if there is someone behind me to avoid dazzling them unnecessarially with my brake lights.

Regards, John.

I think I do that (into neutral and apply the parking brake) unconsciously in both automatics and manual motor cars John. Perhaps it comes of being a biker at heart (less the handbrake bit of course), where holding the clutch open with one's left hand is inconvenient and tiresome?

I still think this is good practice, and find it irritating having to look at another driver's brake lights when stopped at a traffic signal because they have not bothered. I can't help thinking it is better for the drivetrain (in both automatics and manuals) for it to be in neutral when idling - less wear, less heat and less fuel.

Just my view - judging by the number of brake lights I see at controlled junctions and crossings many drivers disagree with me :-).

Alan

[Othen]

Originally Posted by john.wigley

Hi Adam, Is this a recent phenomenon? If so, might it not be a fault as such, but due to the high ambient temperatures coupled with the load or drag on the transmission when you engage D or R? Most of the automatics that we have owned over the last 30 years have exhibited similar behaviour to a greater or lesser extent.

Regards, John.

This has given me an idea for the RB John,

There is always a little drag when the shifter moves from P/N to D/R/2/1 just due to the fluid flywheel never providing zero torque - this manifests itself as creep, which all autos do and is actually quite useful in traffic. When this happens there is of course a slight drop in engine speed because there is no computer (ECU or whatever) to correct it - the RB is entirely an analogue machine.

Now here is my idea to counteract this: the anti-dieseling solenoid isn't really needed so I could reverse its action so it actuates when the shifter is in D/R/2/1, but is isolated in P/N. If I adjusted the tick-over so it was set at 850RPM with the anti-dieseling valve closed, then took a feed from the starter immobiliser (open only in P/N) to a 5 pin relay wired as NC between pins 30 and 87a to the anti-dieseling solenoid, then it would only open in D/R/2/1 - raising the engine speed by a few hundred RPM in those gears only.

What do you think? Would this work? I'll see if there are any comments telling my it won't work - and if not perhaps I'll experiment on the RB with the B21a motor fitted before I transplant the B230 engine.

:-)

PS. I've just spotted a flaw in my logic about using the starter immobiliser - I don't think it wouldn't be energised unless one was operating the starter (I have not checked the wiring diagram, but I think it would be wired in series with the starter switch and solenoid). The problem isn't insurmountable - I could fit a microswitch somewhere to replicate the action of the starter immobiliser.

[john.wigley]

Accepting your proposals for wiring up the device - I can do no other since I lack your specialist knowledge in the matter - your theory seems sound, Alan. It could improve the R.B.'s drivability in slow moving traffic and for that reason alone would be an interesting experiment. You could also easily reverse the modification should it prove not to be successful.

It does beg the question, however, why hasn't anyone thought of it before? Maybe they did and there is a patent out there somewhere, in which case why didn't Mr. Volvo offer it as a refinement to his motor cars in period (possibly cost (?)). Either way, you cannot now lose anything by trying and, since you are unlikely to cause any damage to the R.B. in doing so, why not give it a go? At the very least, it should make for a most interesting thread!

Regards, John.

[Othen]

Originally Posted by john.wigley

Accepting your proposals for wiring up the device - I can do no other since I lack your specialist knowledge in the matter - your theory seems sound, Alan. It could improve the R.B.'s drivability in slow moving traffic and for that reason alone would be an interesting experiment. You could also easily reverse the modification should it prove not to be successful.

It does beg the question, however, why hasn't anyone thought of it before? Maybe they did and there is a patent out there somewhere, in which case why didn't Mr. Volvo offer it as a refinement to his motor cars in period (possibly cost (?)). Either way, you cannot now lose anything by trying and, since you are unlikely to cause any damage to the R.B. in doing so, why not give it a go? At the very least, it should make for a most interesting thread!

Regards, John.

Perhaps it a solution looking for a problem that isn’t important John, and it was of course overtaken by events a few years later when motors started being controlled by computers.

Perhaps I’ll wait and see how the RB turns out with the B230 motor - the slightly larger engine will have a bit more torque and so may barely notice a bit of transmission drag.

:-)