E34 M60 (V8) engine idle query

[pingu]

Hi peeps,

I'm a newbie but I'm been stalking this forum for a little while now!

I sometimes seem to be getting a slow idle (i.e. 500rpm or below). When the idle speed is low, the engine resonates with the chassis and it's no longer an oasis of quiet inside the car.

I'd like to know if this is normal or if something needs fixing.

Once it has warmed up, the idle occasionally fluctuates between about 450rpm and 700rpm - each time I'm at traffic lights, it seems to idle at a different speed. Putting the autobox into Park usually increases the idle speed by about 100rpm compared to Drive. Turning on the A/C also raises the idle speed by about 100rpm. The block has been changed so I doubt it's the Nikasil issue. The spec for the idle speed is 600 +- 50rpm, according to
http://www.e38.org/e32/M60EngineSpecs.pdf

My Indy has already had a look into this and slightly improved things, but I'm wondering if they should have changed the Idle Control Valve instead of just cleaning it.

Thanks,
Olly.

[SharkmanBMW]

welcome,
Since you have an alusil block, you are a step ahead...
could be PCV plate leaking abit?!

Others more knowledgeable than I will help you shortly!

[632 Regal]

try rebooting the computer (search reboot) to start fresh. The V8s are notorius for intake leaks too. Mine idles at 500 weather in gear or not, the AC does pump it up 100rpm.

[onewhippedpuppy]

Mine idles at 600-ish most of the time, sometimes it drops as you describe, and resonates through the car. What helped with mine was cleaning the ICV, dumping the crappy K&N for a factory filter, cleaning the MAF with residue-less electrical contact cleaner (don't touch it), tightening all my intake connections, cleaning the throttle body. It's still not perfect, but as Jeff said, the M60 is notorious for intake manifold gasket leaks, as well as the PCV plate at the back of the intake leaking. Either one can cause an unsteady idle. The good news is if you're the DIY type, both are pretty cheap fixes, I just haven't done mine because I have bigger problems right now.