Newbie question - occasional low/surging idle on 3.9L

discomeans

Well-known member
Apr 13, 2021
123
48
Florida, USA
Driving around my 92 RRC I'm now getting familiar with the annoyances of Rover gas engines. Really looking forward to the 300Tdi conversion.

In the meantime, I have an issue with occasional oddness in idle speed. Driving around town, sometimes it feels like it's going to stall. Turning on/off the AC doesn't seem to make a difference in idle speed.

Based on what I've read, cleaning the idle air control valve is the way to go. My stupid/newbie question is - how exactly do I remove and clean it properly, and do I risk screwing up any adjustments that I'll have to correct after reinstalling it? I've actually searched and not gotten great results on this basic topic.

Mine's a 92 so I think it's at the back of the engine... right?
 

Tugela

Well-known member
May 21, 2007
4,624
415
Seattle
There's a range of potential causes for what you describe. The idle air control valve is on that list and since cleaning it is easy, you might as well do it (especially if you don't know the maintenance history). The part is at the back of the engine, a Google image search might point you to it.

I had a similar issue with my 1993 RR. After cleaning the IACV and messing with the base idle setting (I don't recommend this until you have eliminated other possibilities), I figured out the culprit was the ignition coil. I had installed an aftermarket part and the Prince of Darkness didn't like it. Switching back to a Lucas coil did the trick. Presumably you've checked your distributor rotor - another part about which the 3.9 is picky. Your situation may be different, but hopefully this gives you a starting point for your investigation.
 

Blueboy

Well-known member
Apr 20, 2004
3,035
377
Back in the USA; Rockwood, PA
This might help as well - 94/95 D1s used 3.9:
 
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