# High Idle Switch?



## self_russell (Mar 14, 2020)

Just moved to PA from SC. Wondering about a rheostat or switch to make my X5d idle at 1500RPM to warm it faster. 

Any thoughts or just leave it be and let the thermostat do its thing in a few miles?


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## Doug Huffman (Apr 25, 2015)

What effect does idle speed have on warm up times?

A rheostat is an analogue device that will have difficulty communicating with your DDE. What might be switched to change the idle speed? There is more to warm up than the thermostat. Glow plug preheaters partial load heating and delayed first and second shifts come to mind.

My diesel TDI VW would idle to cold at a stoplight. I doubt the BMW diesel is that efficient but the best way to warm it up is to load it, to drive it. 30 seconds after starting I’ve got mine near WOT.


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## n1das (Jul 22, 2013)

self_russell said:


> Just moved to PA from SC. Wondering about a rheostat or switch to make my X5d idle at 1500RPM to warm it faster.
> 
> Any thoughts or just leave it be and let the thermostat do its thing in a few miles?


I live in NH and it gets a lot colder than PA does in the winter. PA is balmy by comparison. A high idle option is not really needed in a BMW diesel but is nice to have. By "rheostat" I assume you mean a potentiometer added to the go-pedal circuit? You probably could modify the go-pedal circuit so the DDE see the equivalent of the pedal being pressed slightly but it might also trigger Check Engine Light codes.

In my 2002 VW Golf TDI (diesel), the ECU in manual transmission TDIs had a governed high idle mode that you could enable by holding your foot on the go-pedal and brake pedal simultaneously. When in this mode, the ECU maintains a precisely governed 1199 RPM. Loading the engine caused the ECU to automatically increase fueling as needed to maintain 1199 RPM. This mode served as limp mode in case the go-pedal circuit was inoperative. The go-pedal input to the ECU is an analog input from a redundant pair of potentiometers in the pedal assembly. I thought about adding a switch and resistors the go-pedal circuit to simulate the pedal being pressed slightly and adding a switch to simulate the brake pedal being pressed. It would be an easy way to add a high idle option to 1996-2003 model year manual transmission TDIs. The only reason why I didn't bother to do the mod was that I high idle option is not really needed. I am not aware of BMW having this kind of mode built into the DDE in their diesel BMWs.

The one situation I have run into with a TDI was when the car was totally iced up in the bitter cold and I needed to warm it up to de-ice it. That meant I had to drive it to warm it up, but I couldn't drive it until I de-iced it first, and I still needed to drive it to warm it up so I could de-ice it, but I couldn't drive it until I de-iced it. The solution was to switch on electrical consumers to increase the load on the engine to warm it up faster so I could de-ice it and then drive it. A high idle option would have helped in this case.

I owned a 2008 Ford F-350 SuperDuty PowerStroke Diesel pickup truck several years ago and it had high idle capability. My truck had the 6.4L PowerStroke Diesel. The FICM (fuel injection control module in Ford lingo, aka DDE, aka ECU) would automatically increase the idle speed from ~ 700 RPM up to 1100 RPM after 240 seconds of idle time and oil temperature below 140F (IIRC). The idle would slowly increase when going into this mode after 240 seconds of idle while still cold. It was designed to help speed warmup. It would automatically go into high idle in the winter months but not during the summer months based on the oil temp and idle time.

The FICM also had a Stationary Elevated Idle Control (SEIC) for running equipment from a PTO shaft in trucks equipped with a PTO output from the transfer case instead of 4WD. The truck was factory wired for the SEIC option and you could order the expensive rheostat control panel for it or wire it up yourself with a switch and an optional resistor to adjust the RPM. The two SEIC modes were PTO mode and Battery Charge Protect (BCP) mode. I enabled both SEIC modes at their default RPMs using the factory supplied up-fitter switches for accessories. Entering SEIC operation required the vehicle to be stationary, transmission in Park, parking brake set, and not stepping on the brake or go-pedal. Stepping on the brake pedal or go-pedal would cause it to fall out of SEIC operation until all of the safety conditions were met again. PTO mode defaulted to a governed 1200 RPM and adding a resistor from B+ to the speed control input allowed you to adjust the RPM anywhere from 1200 to 2400 RPM and is precisely governed by the FICM. Call it tow truck mode or garbage truck mode if you will for running hydraulics. Battery Charge Protect mode was also known as Ambulance mode where the default high idle was 900 RPM and the FICM would increase the idle RPM as needed and up to 2400 RPM to increase the alternator output to keep the batteries charged (2 12V batteries in parallel). The truck is a commercial vehicle platform and gets configured in many different ways including configurations with heavy electrical loads. Ever notice that ambulances stay idling when on-scene? Ambulances have lots of lights outside and lots of equipment inside which needs to stay powered. Some trucks had the dual alternator option for up to 360A output. My truck had the standard 200A single alternator.

While I love my BMW diesels and they are long term keepers, I miss that truck as it was too damn useful for those times when I needed a truck. At the time is was hard to justify owning 3 vehicles when I am the only driver of them. With BMW not offering anymore diesels in the USA, I probably will have another diesel pickup truck again someday to keep owning and driving only diesel vehicles. I am becoming more of a pickup truck guy too so it's just a matter of time. LOL.

A high idle option is a nice to have but not really needed in a BMW diesel. That's why I haven't bothered with trying to do a high idle mod on my BMW diesels.


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## Doug Huffman (Apr 25, 2015)

n1das said:


> [ ... ]The go-pedal input to the ECU is an analog input from a redundant pair of potentiometers in the pedal assembly. I thought about adding a switch and resistors the go-pedal circuit to simulate the pedal being pressed slightly and adding a switch to simulate the brake pedal being pressed. It would be an easy way to add a high idle option to 1996-2003 model year manual transmission TDIs. The only reason why I didn't bother to do the mod was that I high idle option is not really needed. I am not aware of BMW having this kind of mode built into the DDE in their diesel BMWs.
> [ ... ]
> A high idle option is a nice to have but not really needed in a BMW diesel. That's why I haven't bothered with trying to do a high idle mod on my BMW diesels.


*Accelerator pedal module *
The position of the accelerator pedal is reported to the DME/DDE control unit via analog voltage signals. The signals are generated by two pedal sensors in the accelerator pedal module.

The pedal sensors take their 5 V power supply and ground connection from the DME/DDE control unit. Depending on the operating angle, the pedal sensors return various voltages to the DME/DDE control unit. The DME/DDE control unit converts the voltage signals into the pedal sensor position.

The signal of pedal sensor 2 always has half the signal voltage of pedal sensor 1.

The idle, full load and kickdown positions are detected by way of voltages of the pedal sensors.

Fault handling

The pedal sensors are monitored for short circuit and open circuit, as well as for plausibility in relation to one another.


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## self_russell (Mar 14, 2020)

Im coming from a 92 Ram W250, Cummins 5 speed, a 98 Ram 3500 4x4, Cummins Auto and USMC diesels. 

I understand those trucks are different. They are work horses. The X5 is a family car. 

Thanks for explaining and teaching me gents. Im sure ill have a ton more silly questions.


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## n1das (Jul 22, 2013)

Doug Huffman said:


> *Accelerator pedal module *
> The position of the accelerator pedal is reported to the DME/DDE control unit via analog voltage signals. The signals are generated by two pedal sensors in the accelerator pedal module.
> 
> The pedal sensors take their 5 V power supply and ground connection from the DME/DDE control unit. Depending on the operating angle, the pedal sensors return various voltages to the DME/DDE control unit. The DME/DDE control unit converts the voltage signals into the pedal sensor position.
> ...


This sounds similar to what VW does with the pedal position sensor although I never dug into it. Any modification to BMW's circuit in the pedal module (B10) would require modifying both signal inputs to the DDE to prevent triggering plausibility errors.


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## Michael47 (May 9, 2014)

Diesels generally do not warm up at idle, certainly not like gas vehicles do. All the diesels I've had could be left idling forever in cold weather and never reach operating temperature. The only way I ever found to warm one up was to get in it and drive away.


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## n1das (Jul 22, 2013)

Michael47 said:


> Diesels generally do not warm up at idle, certainly not like gas vehicles do. All the diesels I've had could be left idling forever in cold weather and never reach operating temperature. The only way I ever found to warm one up was to get in it and drive away.


That agrees with my experience. You gotta get in it and drive away to get it to operating temperature. This creates an issue when the car is totally encased in ice and you have to de-ice it before you can drive it. But to de-ice it easily, you need to warm it up first but you can't warm it up until you drive it, etc. This is where it would be nice to have a high idle option to speed the warmup. A solution in this case is to turn on electrical consumers to increase the load on the engine from the alternator.

In NH, we are required by state law to remove all snow and ice from vehicles before getting on the road. The fine for a single violation can be as high as $1k. The concern isn't over the small amount of snow that immediately blows away when you drive it. The concern is large chunks of snow and ice that can smash windshields when they let loose while on the highway. When the car is totally encased in ice and snow, it's hard to to de-ice the car when it's not warmed up yet. In NH, ice and snow has to be removed from the entire car, not just the windows. It's not as simple as just scraping the ice from the windshield and other windows. I prefer to melt the ice and snow off so I can remove it easily without having to use an ice scraper on the windows.


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## Doug Huffman (Apr 25, 2015)

My junior local cop’s favorite ticket is Obscured Windows., Probably influenced me to learn about hydrophobicity.

OTR semi-trailers are dangerous in winter. Best be clear behind or clear ahead when they dump their roof load of snow and ice. Last year I was sure that I had lost my sunroof glass for the mighty BANG, to the point that I pulled off the interstate and retracted the shade. But no harm no foul and a good lesson.

Experience is a good teacher. A bad experience is a better teacher.


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## self_russell (Mar 14, 2020)

Im not talking about the car sitting at idle. Im talking about it sitting there revving at 1500-2000 RPM. To warm it.


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## Michael47 (May 9, 2014)

Simply revving it up isn't likely going to help. It needs to be under load to warm up fully. But if you find out otherwise, please do tell us about it here, OK? We'd really like to know. Honest.


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## ghpup (Nov 19, 2008)

self_russell said:


> Im not talking about the car sitting at idle. Im talking about it sitting there revving at 1500-2000 RPM. To warm it.


What these fine people are trying to tell you is that it is necessary to load the engine with more than just higher revs. For me, with temps in the teens lately, I get the vehicle to operating temp in about 15 minutes of driving. Fortunately, the heated seats and steering wheel are faster, as is the heater/defroster. I suspect the heater/defroster get a boost from somewhere other than engine coolant temperature, but I am not all that mechanically inclined. My personal comfort is not jeopardized for very long by the cold ambient of the inside of the vehicle.


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## Doug Huffman (Apr 25, 2015)

ghpup said:


> I suspect the heater/defroster get a boost from somewhere other than engine coolant temperature,


Yes, diesel BMW have a 1000 Watt PTC heater for the front seats, and some have also an electric air heater for the rear seats.


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## n1das (Jul 22, 2013)

Switch on electrical consumers to help load the engine for faster warmup following a cold start, particularly if you are forced to wait to get some warmth in the car to help with de-icing the car before you can drive it. Switch on the fog lights, seat heaters, steering wheel heat, rear defroster. I leave the sun shade open in the winter to help get warm air inside the car up to the moonroof glass for easier clearing of ice and snow.


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