Re: SPARK PLUG RUST COLORED FOULED
Have you replaced the plug and tried it again, if it still misses at idle than it may have a big problem or just something silly like a vacuum leak at the cylinder which will result in that cylinder not getting fuel at idle, that can cause your plug to discolor and look different to the others. A couple of things you can try before you start pulling things off it, does the engine have the PCV line plumbed into the inlet runner for no.4? If so try slipping the hose off and put your thumb on the port and see if the idle improves, if so you may have found your problem, that being a faulty PCV valve or a crack in the vacuum line. You can also try applying a small amount of oil to the area where the inlet manifold meets the head at the no.4 inlet port. If it is sucking air at that point the oil will fill the void for a couple of seconds and your idle may pick up for a moment or 2. If so than you may just have a blown manifold gasket. A miss at idle that goes away as the RPM increases is often vacuum related, as the RPM increases the airspeed in the manifold increases, the cylinder starts getting fuel and the vacuum leak becomes less obvious. <br /><br />Good luck!
