Idle problem with 1.8 SOHC

That's for all the Protege 90-93 with the 1.8 SOHC owners. I owned a 323 LX last year with a 1.8 SOHC and now I have a Protege with the exactly same mechanical parts so I know them pretty well ;). The problem is those two cars both had a strange idle.... It's not very easy to explain... Every time the clutch is released, before going back at a normal ~750rpm idle, the engine tempt to go off with an rpm going under 350... I have notice that it's a amplified when it's raining... I know that it should sound like a problem connected with the ignition system (plugs, wires, distributor, etc...) but everything is brand new. The exhaust, battery, alternator, air filter, oxygen sensor are in perfect shape, I don't have any trouble code in the computer. Maybe it is a problem with the gaz pump or a vacuum leak? I'm wondering if one of you guys could help me, it would be really appreciated! :D

i apologise about my poor writing, i'm not used to do it in english :D

Check the engine to frame ground wire...most times they are corroded...