The replacement thermostat arrived and duly fitted - only to discover the housing cover, being plastic and obviously subjected to extremes of temperatures, cracked off at the hose part! Fortunately enough was left to cram down tight the Jubilee clip and hopefully last until a replacement is ordered.

The original was distinctly orange in colour and wide open when warm but failed to close completely when cooled so had clearly failed 'safe'. The new thermostat got the engine warmed up within minutes from cold this morning and reads around 87 degrees on the dash temperature gauge (the thermostat itself had 87C stamped on it).

While fitting the thermostat I reconnected the cold-start air-enrichment device as well as a pipe that was so awkward I left it off last time - the one that connects the fuel-return device to the rocker cover oil to air filter pipe (it's only been off for 10 days or so, probably explains the marginal drop in MPG for the fill-ups during that time).

The revs stayed around 1500rpm when testing it on a drive last night, but this morning it returned to 1000rpm cold and 800rpm warm.

I parked up at work and got my trusty 3mm Allen key out and started adjusting the idle to get it back down to the more normal 600-650rpm however each 1/8th turn lean increased the vacuum gauge (needle moving to red / to the right) a small amount and the engine progressively heading to 'stalling' out. So it's back to zero on the vacuum gauge and 800rpm.

The switch on the throttle linkage within the engine bay, if pressed, drops the revs to near 600-650rpm but as I stated in a previous post on this thread it never engages at idle - it is a manual press by hand that activates it. I shall see if it can be moved slightly so that it engages since adjusting the linkage screws did not make this happen (I did find the gear shift line and set that to 3000rpm before changing up a gear).

I have learnt a lot about engines over the years, I even stripped down an MG Metro engine and rebuilt it with tuned parts to wrap my head around how each part functions. Having bought this Benzo just a few months ago I know almost all there is to know about fuel injection and the particular oddities that these cars have - what a learning curve! May I give my thanks to azurite300E for clarifying how EFI can work without an o2 sensor since myself and tvpierce were clearly under the illusion you couldn't have one without the other.

And rorypff I nearly fell backwards off my chair when I read the idea of driving at 120mph to get maximum efficiency! Going just over 50mph will get you banned for a month, and finding a road long enough here on this island in which to reach 120mph is a challenge in itself! Typical driving is stop-start stop-start so its very much 'urban' driving all over the place.

Many thanks, and kind regards,

Glyn B.