Does the vehicle have 4 wheel drive? There is definitely a vacuum leak in the HVAC vacuum supply. Which could be causing the low lambda voltage. Possibly a faulty vacuum check valve. Is the vehicle right hand drive or left hand drive? In the image below, you can see the power brake booster and master cylinder on a left hand drive vehicle.

 

Your welcome for my response but the thanks goes to captain! He's far more knowledgable than I with the tech side so your in about the best hands you could hope for at this point as far as I'm concerned!

 

Captian yes it is a 4x4 and I am driving on the same side as you in the US.

Only UK still have Pounds as currency & driving on the wrong side.

Shall I start plugging the cuircuts ti identify the leaks cuircut?

BR
Bob

 

Today I made some test with my vacuum tester. The Reservoir and vacuum switch are leak free. The line to the AC pannel looks to loose some pressure. The check valve is OK but i habe replaced it. Will See if it works now after i habe replaced some lines.
BR bob