fitted with the X18XE or X20XEV engines. It is also applicable to other models and engines but I will concentrate on the Vectra for this post. It really should be looked at every service rather than waiting until it starts cutting out.Basically, the inside of the throttle body gets coated in an oily black substance (from the engine breather system) around the butterfly opening. It can cut the airflow through the aperture and the idle speed control valve will struggle to keep up with demand (especially if that is also grimy). This is how to check and clean it:
1) Disconnect the multiplugs from the mass air flow meter and air temperature sender.
2) Unclip and disconnect the large breather hose from the rocker cover to the inlet hose. If this hose has collapsed and the rubber softened, replace it.
3) Remove the air inlet tube between the airbox and throttle body. Check the underside of the inlet hose for splits in the corrugations. If split, replace the hose. Don't use tape, it won't work - but will get sucked into the inlet manifold.
4) Unclip the remaining breather hose from the rocker cover (much smaller than the other one) and try to blow through it. It usually gets blocked where it joins the throttle body itself. The way I usually remove the blockage is to pull the hose off the throttle body, take a paper clip, straighten it out and push it through the tiny hole in the body itself. Sometimes it can take a little bit of poking around but will usually remove the buildup. It should push right through with ease.
If you can't get it through, it will be better to unbolt the throttle body and clean it off the car. This will involve disconnection of the TPS (throttle position sensor), the idle control valve and fuel lines so be careful and take precaution for pressurised fuel.
5) Providing we are at a stage where, one way or another, the breather hole is clear, take a rag and either an aerosol of carburettor cleaner or cellulose thinners (I prefer thinners) and hold the throttle butterfly open as you wipe around the aperture. Clean the throttle butterfly too but be careful on the edges as they are sharp and will cut your finger. Make sure it is completely clean where the butterfly closes. If you've removed the body, fit a new gasket unless the original is pristine.
6) If everything is clean, refit in reverse order and start the car. If, after following these instructions, idling is still a problem, the idle control valve could be faulty. A well aimed tap on the body of the control valve with a screwdriver handle can prove a point (it will normally cut out when hit or suddenly change from high to low revs). This can actually be cleaned but isn't always successful and, if I'm honest, is better replaced.
