Idle speed "hunting"

Happy new year to you all.

Only have a small issue that I'm looking into at the moment as my Rover has been behaving very well recently. I have a 2001 4.6 Vogue, obviously with a Thor V8 and 85K on the clock, which is a petrol only car. Had a slight rough running engine due to shot ignition leads, this was most noticeable when starting from cold on wet / damp days. The roughness would disappear when the motor warmed up. This was cured by fitting new ignition leads and plugs as well as all the other service stuff like filters etc.

Problem I've noticed now is that the idle speed varies between 600 and approx 900 RPM. When I mean varies it sort of hunts, in that I can watch the tacho needle rise and fall between these two speeds. It happens only when the engine is warm and in N and also when in D while holding the car on the brakes.

From the reading I've done so far in Rave and searching on here I understand the idle speed is controlled by the engine management CPU and should be a steady 600 RPM. What I don't understand is the mechanism behind controlling the idle speed.

I do have a BBS FAULTMATE MSV-2 Extreme with all the modules enabled for this car, but I have not really used it in anger to date.

Any advice would be welcome. I hope to get the time over the weekend to hook up the faultmate and have a look around the system. Additionally my Cats have been rattling for some time, but that has sort of stopped now. I'm wondering if the erratic idle and the cats are linked. I think there is a test I can do on the cats with the faultmate. Anyone done this?

Cheers,

Carl....

I had this issue on my 3.9 Disco - it could be a vacuum problem (air leak somewhere). Check for any holes, slices etc in the vacuum hoses going to and from the airflow meter. Is the exhaust blowing at all with the catalyst rattling, as I knowing blowing may not help either.

And Happy New Year to you sir!

Hunting on tickover indicates an fuel/idle air inbalance.

Had a similar problem. Possibly a duff lambda. Read off the codes and if so it'll tell you which one.

So I connected up the Faultmate yesterday and checked for stored error codes. No error codes stored in the Bosch Motronic memory. I ran some live captures and have uploaded some screen shots here in the hope that one of the forum Guru's can interpret these and confirm the values look good. I have to say the various values mean little to me.









Now the only thing I decided to do while the Faultmate was connected was to reset the Adaptive settings back to default. Didn't have much time to check anything else as it was late. Do these numbers look good to anyone?

Carl.....

Is a BBS MSV-2 Extreme not more than just a code reader?

Throtte stepper motor about 80% of the time. Easy enough to open with a couple of screwdrivers and clean out with carburettor spray (not contact cleaner or WD40). You can do the MAF sensor at the same time and if it were me doing all that I'd renew that air intake filter and this is when I would reset ECU adaptive trims. No harm that you've done it already but no benefit either. Then drive it around for a week, mix of long and short runs and over a couple of 100 miles the trims will have re-adapated.

If that doesn't fix it then you're out of luck because as Wammers said its a fuel and air problem so you'll have both systems to investigate plus the ECU control system (sensors, harnesses etc). By the way your lambda's look ok but are they switching as they should? Only looking at live data can tell. If constant there is problem.

Good luck!

Thanks for that rasheed. Air filter was replaced with a new K&N in August so am assuming that is still good. Have to drive up to Nottingham tomorrow which is a round trip of about 300 miles for me so will see how it goes.

So when I do another live data check what am I looking for regarding the lambda data values? Should I drive the car around for the test or just have it idling and stationary?

Thanks, Carl....

The Maf reading could be a bit low - 26kg/hr at 830 rpm is not too good.Might pay to check it again and see what it is at around 650 rpm,I'd like to see 22-25kg at that speed.(90+ at 3000 rpm,engine running free is good as well )
The fuel trims are in the parish and the misfire counts look good,there cant be too much wrong.

lambdas voltages are higher when the fuel mixture is rich and lower when the mixture is lean. As the ECU tries to achieve its ideal mixture successive cycles will be slightly over-rich or slightly over-lean causing the lambda readings to flick back and forth between two values. Those values themselves vary with rpm and load (the range is about 0 - 5v I think) but will stay fairly constant at any given rpm and load. So no you don't have to be driving it around, just watch that they are flicking.

Idle problems now fixed. Solution was to clean out the Idle Air Control valve with throttle body / carb cleaner. No more hunting or fast idle issues, stays at approx 600 RPM.

Lone_Wolf said:

So I connected up the Faultmate yesterday and checked for stored error codes. No error codes stored in the Bosch Motronic memory. I ran some live captures and have uploaded some screen shots here in the hope that one of the forum Guru's can interpret these and confirm the values look good. I have to say the various values mean little to me.

Now the only thing I decided to do while the Faultmate was connected was to reset the Adaptive settings back to default. Didn't have much time to check anything else as it was late. Do these numbers look good to anyone?

Carl.....

Click to expand...

Hi
I came across this when I was searching for some info on faultmate : I have an MSV-2 and I have a licence for SMO-7 : which of the downloads was producing the info you copied here ? I just want to get the appropriate one for monitoring the 2.5D engine ('97) : thanks and sorry to pull this up after a couple of years !

For the diesel i belive you want bosch edc sm007 download.