Hi all,
I've googled extensively on my problems, and there seem to be many possible
causes, so I'm posting my symptoms here in case the combination rings any
bells.

1990 UK 520 with 168k miles, bought recently. Engine sounds great, exhaust
is blowing but no tappet noise (my last 518 w/m40 certainly had tappet
noise).

The temp guage would not leave the blue zone, so I changed the thermostat,
and now it stays just above the 1/4 mark - an improvement, but not where it
should be. I got the 'stat from Eurocarparts. The rad blades spin freely
when engine is cold, so I guess the coupling is ok.

Idle is low & rough when engine is warm, hunting between 500 - 900, or
sitting at ~600. This makes the car shake a bit at lights, and if I have to
slowly manuevur, the low revs result in power steering stiffening up, & can
cause an engine stall. Oddly, this low / hunting idle problem is worse in
the evening when I drive home from work, than in the morning when I set off.
More sitting in traffic on way home?

Economy was ok on a recent motorway run, 460 miles from a tank at 80mph, but
I only got 260 miles from a tank when driving about town. Driving style
certainly a bit at fault here, but even so..? Tank of fuel costs ~£55.

I've had all the belts changed, and a basic engine service (plugs, filters,
oil change) - oddly the engine seemed rougher at idle after the service than
before.

After googling, possible faults include Idle Control Valve, Air Flow Meter,
vacuum leaks, Fuel Pump Relay, Throttle Position Sensor. I had a look at the
engine bay, and saw a big ribbed rubber hose from the air filter, which
looked quite new & ok - how else can I check for vacuum leaks? (after
googling, I went in to Halfords and asked for some propane spray, principle
being that the engine would race if the spray hit a leak. I explained this,
and the assistant looked at me like I was insane!)

I don't know where the ICV, TPS & AFM are, but I'd like to eliminate vacuum
leaks first anyway, are there any other ways of tracing them?

Many thanks for any help!

Jamie