Engine stuttering

[Chim2018]

Hi

This afternoon my 4.0 Chim engine has started stuttering when idling. It drops to between 400 to 500 rpm then pulls itself back.

I only cleaned and resealed the stepper motor a couple of weeks ago and when plugged into the rover gauge software and then opening the stepper by 30 steps the engine revs increase.

So my original thought of needing a new stepper motor doesn’t appear to be correct.

Any ideas please?

Thanks

[ianwayne]

Has the base idle screw on the plenum (inlet side) been left screwed all the way in? If so, this will block the air bleed and the ECU cannot increase air into the system via the stepper motor.

[Chim2018]

Thanks for the quick response.

The screw appears fine and when the stepper motor is operated using the rovergauge software the engine revs increase. Is it possible for this to happen if the screw is more closed than open?

[ianwayne]

This is from memory (last Chimaera with a stepper motor sold in May 2017) but when you set the base idle at about 600 rpm with the stepper motor supply hose blocked off or clamped shut, when you release it the revs should bounce up to 900 rpm ish on a warm engine. If it doesn't, you've turned the screw all the way in and blocked off the supply.

The ECU has no stepper motor position feedback, it starts from zero every time you start the car (it motors it all the way back on ignition off), and then motors the plunger in and out to regulate the air. If the stepper motor is sluggish to respond the ECU doesn't know and will continue trying to motor it in and out with pulses. I had a Chinese one in my last one that would idle at 2000 rpm when cold, which was sorted by a genuine Lucas one.

[SILICONEKID 357HP]

Is it shy ?