If this sounds like a ridiculous question, bear with me!

Moving the gear selector to 'N' on my car does exactly what you'd expect it to do - it puts the gearbox into Neutral. The 'N' indicator doesn't always illuminate unless you give the stick a wiggle - but that's hardly interesting in itself! What is interesting is that once you do get the 'N' to illuminate, the car starts to idle more smoothly.

Is the selector switch separately 'telling' (not an electronically controlled 'box on the 3.2 remember) the gearbox to shift, and also informing the ECU that it's in neutral?

I guess I just need to have a look and clean/adjust the switch, but I am curious as to what's happening - anyone know?!

 

I and a few others have had the reverse problem: smooth idle in gear, rough idle in "P" or "N".

I've tried asking and learning specifically what the engine management system does when it learns the trans in in "P" or "N" but don't reall hearing definitive answers. Presumably it shorten injector pulse width to compensate for decreased engine load, if nothing else?

It will be intersting to her any new thoughts on the subject.

Cheers
DD

 

The 'linear switch' on the side of the shifter does indeed tell the ECU that the transmission in in "P" or "N", even with the non-electric transmission

Cheers
DD

 

Mmmmm, I have never thought of it that much.

My 3.2 has had that linear switch cleaned and reset the day after I got home with it, waaaaay back. I have had sooo many issues with the daughters '40 with that switch I simply just did it.

There is a LOT of wires coming out of the X300 awitch, that I reckon it does a whole lot more than we suspect, and Dougs thoughts on the injection pulse is more than reasonable.

Mine idles just fine in gear or out of gear, a/c on, or off.

 

Hi Ziggy,

I just consulted the AJ16 Engine Management System Dealer Training Manual and the answer to your question appears to be with the ignition timing control and IACV control. The ECM fueling control has no input from the TCM or decoder module, but the ECM ignition control receives a signal from the decoder module indicating when Park, Neutral and Drive (and presumably other forward gears) are selected.

According to page 6-3 of the manual, the ECM uses "Separate closed throttle ignition strategies for gear positions Neutral and Drive."

According to page 6-6, "The ECM uses inputs received from ignition ON, the crankshaft position sensor (CKPS), engine coolant temperature sensor (ECTS) and throttle position sensor (TPS) as well as inputs for ignition ON/OFF, gear position, air conditioning compressor operation and road speed to control idle."

According to page 6-8, "When the gear selector is in Park or Neutral the engine management ECM receives a ground signal from the transmission decoder module. The ECM then closes the idle air control valve a predetermined number of steps in anticipation of the reduced engine load. At idle, the ECM applies ignition timing from separate closed throttle ignition strategies for gear positions Neutral and Drive."

Hope this info is helpful.

Cheers,

Don

 

Thanks all - that certainly satisfies my curiosity It's not that it idles particularly badly before the 'N' illuminates, just that there's a difference - which I now understand!

Another job on the to-do list...