I've been doing lots of reading up on NAM and other sites regarding issues with rough idle (which I have), stalling (which I have), wiring harness replacement (which I have had) and other ECU related topics. I'm now trying to determine the mechanism with which the ECU regulates the idle of the engine. In looking through the web, other cars seem to have some sort of "Idle Control Valve" which is somehow controlled by the ECU -- it bypasses the throttle plate and allows some air into the intake at idle. I haven't seen any information about the MINI engine having a valve like this, so I'm wondering if it exists, or does the ECU just move the throttle plate itself to regulate idle (since it is ECU motor driven).

A second question revolves around what sensors/data does the ECU use to make a decision about idle speed regulation? I know there are a bunch of sensors on the engine, but am wondering which one(s) may be providing the data input for idle.

I noticed an interesting phenomenon today as I was datalogging a bit with my OBD-II scan tool. When the car is started completely cold (sitting overnight), idle speed is set relatively high at ~1100 rpm. As the engine comes up to temperature, the idle speed very gradually decreases over time (not in a stepwise manner, a very linear smooth reduction) until it gets down to the normal idle speed of ~800 RPM. This tells me that the ECU is exercising some very fine grain control over the idle speed based upon some input data.

I was able to capture a bit of my rough idle problem with the datalogger software, here's a screen shot:



You can see the idle speed jumping all over from 600-1000+ rpms. The top graph is coolant temperature. This started to happen just as the ECU was transitioning all the way to the ~800 RPM idle.

_________________
BigBrownDog
2002 MCS Chili Red / White
Team SES candidate
Webb EVM Package
Collinsville IL / St. Louis MO Area

 

While I can't help you with your problem, I can tell you how the ECU controls idle.

For very fine adjustments, say a couple hundred rpm, it will adjust ignition timing.
For larger adjustments (for cold start idle, and when the engine is heavily loaded from A/C, high alternator load) it opens the throttle a bit. Since the throttle is already electronically controled through the drive by wire system, the ECU can move the throttle on it's own.
This method eliminates the need for an idle control valve found in many other cars.

 

Thanks for the timing-control information.

I can;t do it right now, but tomorrow, I'll record the timing, coolant temp and RPM
during warmup on my 02/02 MINI Cooper 5-speed.

It's not the same thing an your MCS, but more data is better right?

Here's an OLD capture of timing of ignition advance vs roadspeed.
(See how the advance goes After TDC when cranking? That's pretty cool)

 

Hey Trippy -

what are you using to collect the data? I've just started using the Digimoto software, and in their latest release V3.7, they have a datalogging capability. I can only access OBD-II data, but it does include about 12-15 things like temp, timing advance, fuel trim, rpm, MAP pressure, etc.

My car is back at the dealer as of this morning, it went into EML mode at 60 MPH as I was driving it to the dealer to drop it off. *That* was a pleasant experience.

 

I'm using the same scantoo.net ELM-ISO board that you have with your
digimoto software, but I wrote a C program that runs on Linum and grabs
the OBD-II sensor reading I select and saves them to a file.

I'm 99 and 44/100 percent sure you don't want my software, but if you DO,
I'll send it to you.

Then you process it with VI or whatever your favorite text editor is and
plot it with gnuplot. Blech!