AC Idle bump

[übersteuern]

On my M52 (running the OBD2 DME from an automatic car), I found that clearing the adaptions helped stabilise the idle heaps. Where before the revs would drop really low and sometimes stall, now it falls back to idle no problems.

Yeah it's a bandaid solution, but it does help a lot.

[325e10]

On my M52 (running the OBD2 DME from an automatic car), I found that clearing the adaptions helped stabilise the idle heaps. Where before the revs would drop really low and sometimes stall, now it falls back to idle no problems.

Yeah it's a bandaid solution, but it does help a lot.

Adaptations? can you clarify that a bit more for me? not sure i'm understanding it.

[übersteuern]

Over time, the ECU learns the engine's running characteristics (eg rich/lean from the O2 sensor) and adjusts for it. Resetting the adaptions means it starts from scratch.

I had a mechanic do it, but I think there are ways to DIY.

[caesar101]

I seem to have my idle bump working on a OBD2 M52. I did not do the wiring on my swap so this is the first I looked at this problem. Violet/ gray wire from pin #16 was connected to the +12 a/c signal in the glovebox. Applying power on and off while idling did nothing. In the E36 the radiator fan is started by the a/c control and the same wire goes to pin # 16 on the DME by way of the pressure switch. To start the fan the control unit grounds this wire thus grounding pin #16. I installed a relay to ground pin #16 when power is applied to pin #19 and idle bump. It is not perfect but works much better. I am guessing the DME also delays the compressor start to allow the engine speed to come up first, but that would require wiring the compressor to pin #74 with another relay to start the compressor to test. I need some road time now to see if it is consistent.

[MC Hammered]

correct. driving is fine, it's only when you come to a stop that it hunts for a few seconds and then evens out...

still like to know how to eliminate that though...

I am having this issue as well and the hunt is almost like a timer is going off as I hear a click, RPMs drop and then recovers and this repeats. Odd thing is this does not happen all the time and is seemingly random.

Does your wiring setup look similar to mine? The pink/white wire is input to DME

[jrez]

Been awhile since I looked at this(like 10 years) but I seem to recall the e36 dme gets a a/c compressor "on" signal from the climate control module, which I recall was not an analogue dc signal. Think it was square wave DC. The analogue(high/low pressure switches) on the e30 hooked into the e36 dme will do nothing to increase the idle. I tried also years ago.

[328ijunkie]

E46's they started (somewhat) PWM compressors and stuff.
The E36 just uses basically 2 signals into the ECU, one from the 'AC button' and one from the pressure switches. When both conditions are met, it fires the compressor itself.

[Wishno87]

So where are we at with this?

[MC Hammered]

Troubleshooting this got put aside, the last step I was at was to determine if there is power getting to pin #9 and seeing if the software I have is correct or not.

[nrubenstein]

Yes, the AC idle bump works. Hell, it works on my Euro motor with an MSS50. I can even see the DME report AC as on when I flip the AC button. It worked on my S50US as well.

[MC Hammered]

What line are you connecting the AC switch to at the ECU to trip the idle bump?

[nrubenstein]

What line are you connecting the AC switch to at the ECU to trip the idle bump?

X20 pin 6, iirc.

I don't like hacking up the harness if I can avoid it.

[sweet3]

anyone figure this one out yet?

[Navarone]

AC Idle bump

I'm restoring a Tron arcade game at work, is beautiful, like new, thanks for asking. Anyway, it also has a grey wire and a violet wire that used to go to the original power supply that had an R-C circuit that would pulse +5v on-off-on when the game boots and that would reset the ram and allow the game to run. Now that we have a switching power supply installed we no longer have that R-C circuit and the game won't boot. What we have found so far is that putting +5v on violet doesn't boot every time, but putting +5v on grey boots 90% of the time. We're thinking of building a circuit to replicate the proper timing sequence, or just the effect of clearing the ram, but there are other work arounds we will also try.

We'll see how it goes.



I know that has nothing to do with your car, but I have grey and violet wires and weird old technology to troubleshoot too. Good luck!

[MC Hammered]

I haven't checked my AC wiring since my last post, time to bump this up on the todo list.