MoTeC Global Forum

Hi all,

I'm running a Volvo OHC 4cyl using a 2-Group 3D box, which I believe has been flashed with the most recent firmware that was written (V4.2 Revision E ... I think). I've got some odd-control behaviour, and was looking for any thoughts or suggestions.

Firstly, I have had advice from MoTeC tech support (Andrew?), who sensibly suggested it'd be best to just tune the car to want to idle at ~950rpm using fuel & spark. Then use idle-control as a backup to that. I've only just added an O2 logger & rebuilt the head, but hopefully soon I'll be able to tune it properly.

Anyhoo, it has always displayed some odd behaviour when idle-control is working. If you let it drop through about 1500rpm, then it settles itself quite happily, regardless of how quickly it's dropped or what temp it's at or what sort of load it's just been under. But if you touch the throttle when it's under about 1500rpm, then it starts to hunt & starts to act like it's badly underdamped (if I remember my control-theory geektalk properly). Changing the gain & ?damping? factors doesn't seem to have any effect at all; and I'm using an IAC valve from a 4.1L EEC4 Falcon (potentially too big for a 2.3L engine). It's something that's fairly easy to get around by blipping the throttle so it goes over 1500rpm & then leaving it alone; but the car would be so much nicer to drive without the need to do that.

I've heard rumour that idle-control in these (admittedly ancient) ECU's wasn't the best ... guess I was just wondering if anyone else had experienced the same, and/or worked out a way 'round it?

Getting Idle working can be tricky.
Some things to consider:
The MAP sensor must be connected to the manifold.
The engine must be "dynoed" first, setting up Idle control is the last thing that is done.
Firstly you must get the engine to Idle correctly 50 to 100 rpm below the desired idle rpm when it is hot without the valve.

I would suggest no more than 6 to 12 degrees ignition timing with the sites around the desired idle rpm set to the same value as the idle rpm site. Set the fuel sites around the idle rpm site with similar values as the idle rpm site.

In the software set the AP parameter first with GF & DF at 0. With the engine hot, adjust the AP value until the engine increases RPM then back it off slightly.
Then adjust the GF value until the engine just starts hunting. Then adjust the DF value to stop it hunting
Try to use small values for GF & DF.
Now you need to let the engine cool down, waiting a few hours is best. With the engine cold and warming up only make small changes to GF and DF. This process may take several warm-up starts to get it right.

Also remember an engine with big cams and no air speed at Idle will be difficult to get it right.