Thread: Rev's fluctuating at idle

25 rpm? Not 250rpm?
You’re noticing a 25 rpm change? I’m impressed

Originally Posted by DiscoJeffster

25 rpm? Not 250rpm?
You’re noticing a 25 rpm change? I’m impressed

Yep 25 RPM , spent my life around engines that run constantly on boats , so usually tune in to how they sound.

I should add 2008 with 148,000ks. Gearbox serviced at 72,000 & 140,000 and seems smooth without and noticeable shudder.

I wonder if a failing EGR or 2 would cause this sort of issue.

Cheers Ean

I can’t help sorry but something in the closed loop element will be a factor. Anything the provides air is of concern, anything that affects mixture etc, eg o2 sensors. The engine will be doing what it can to maintain idle set point and the fluctuation indicates something is causing ongoing adjustment. An air leak for example could cause the throttle to adjust to compensate. I expect what you’ll find is that in not too long the ECU will flag up the issue at hand. Have you had a look in the manual for fixes for the symptoms?

Originally Posted by DiscoJeffster

I can’t help sorry but something in the closed loop element will be a factor. Anything the provides air is of concern, anything that affects mixture etc, eg o2 sensors. The engine will be doing what it can to maintain idle set point and the fluctuation indicates something is causing ongoing adjustment. An air leak for example could cause the throttle to adjust to compensate. I expect what you’ll find is that in not too long the ECU will flag up the issue at hand. Have you had a look in the manual for fixes for the symptoms?

Thanks - You must have a better manual than me , as all mine says is how to operate things in the car. I don't even think there is a fault finding section in it.

Cheers Ean

Hey Ean,

Any further progress on this? Noticed my d4 2011 3.0 is also fluctuating at idle, although a quick change of approx 50rpm down or 50rpm up from around 710rpm.