Cold start valve INFLUENCING the oil pressure gauge?!!

[w124uk]

A weird thing happened - I've disconnected the cold start valve (in attempt to find the cure for a long cranking before the engine started from cold). It looks like starting actually did improve (I need to wait for the engine to cool down properly before I'm certain)....
The problem is the engine oil pressure gauge is acting in a strange way now..... as soon as the engine starts it goes to full 3 even at low revs (600rpm circa ) - before it used to be around 1 and would go up to 3 only at higher revs....
Any ideas????