Thread: 3.9 RR - Rough Idle in Drive on LPG & Petrol

Not sure if this will help (without Pics) but it may not be that. I had the same thing and found the Brake vacuum line was sucking air at the plenum. Otherwise a pic would be good

cheers

Loyd

I'm guessing the cleaner was CRC carb cleaner - not sure of the number, sorry - But I would check the spark, if it's running rough on petrol and gas.

shayne

Same happened to me.
Check all cacuum lines, similar to the vaccuum in your head, when lines come off things go wrong.


Hehehehehe

Hi Big Guy,
Checking the parts catalogue, I can see that the part that needs attention is actually called the "Stepper Motor", which is part of the idle control assy.
Now all I need to remember is what was recommended for cleaning the parts..
I'm sure it will come to me..
Cheers,
Shirley......

There are number of reasons an EFI 3.9l will run rough at idle. You can try cleaning the throttle body and idle air control stepper but this should not make the engine idle rough, just mess up idle speed control.
Here some more likely things
Leaking inlet manifold or vacuum line, plugs tired, leads tired, rotor button not a genuine Lucas, head gasket, burnt valve, MAF sensor.
What can be confusing is that these engines will idle a little rough on petrol sometimes even when there is nothing wrong. If everything is OK though then LPG idle should always be smooth.
What is most significant is that it idles rough on LPG. You could be heading for a big backfire which could cause some expensive damage. You should take it to someone who knows these engines.

Originally Posted by Shirldownunder

Hi Big Guy,
Checking the parts catalogue, I can see that the part that needs attention is actually called the "Stepper Motor", which is part of the idle control assy.
Now all I need to remember is what was recommended for cleaning the parts..
I'm sure it will come to me..
Cheers,
Shirley......

Throttle Body Cleaner (available at Repco, Supercheap etc) is what you need. Clean the stepper motor with that and squirt a bit of cleaner into the hole the stepper motor came out of.