Hi all,

My B230E manual says the idle is supposed to be 900 rpm. I've adjusted my idle around 750. First I find that mileage is better especially if stuck in traffic and second the engine (B230E) feels too powerful at 900 rpm base idle compared to a b230F engine with similar idle rpm. What I'm wondering is could this bad for the engine or tranny or exhaust mounts. There's a bit more engine shaking at 750 than 900. And how do the volvo engineers come up with this 900 rpm. Should I just stick to spec? Otherwise the car runs and starts fine.

Thanks in advance.

Volvo cams are traditionally good but camshaft manufacturers feel that higher idles reduce the load on the apex of the lobe. This is mostly an issue at break-in but conceivably could result in metal to metal contact, although the Volvo "trough" of oil is one of the better OHC oiling arrangements I've seen.
You'll likely have no problem but I've analyzed camshafts for 12 years and have seen hundreds of failures due to break-in procedures that were a result of metal to metal contact.

While I am always in favor of doing what the manufacturer recommends, 750 seems reasonable as an idle rate (that's what all B230F/T engines use). You need to keep oil pressure high enough.