Vauxhall Monterey engine wont start after putting new ht leads on

We put new ht leads tried to start the engine but no go, its a auto,so changed back to the old ones, still wont start, we have got a immobilizer on it but dont think its got anything to do with it,never had this problem before.I took a small black cylindrical thing which had a spring, and a plunger on the end of it, which had a load of wires go to it, which went into a housing near the throttle gear off, and cleaned it with ether, i dont know if this is the problem (this part looks as if it shuts off air or something like that or a solenoid)