Rory Fraser

so my car misfires pretty bad at idle (8-700 rpm) as soon as it gets a tiny blip of gas it goes away but when the revs fall back down it starts missing again but it is only at idle this all started when i replaced my alternator i put gas in the car from a jerry can which could of caused it i jb welded my egr pipe my cop and wires are good but i havent checked my plugs what else could cause this it runs rough shakes a bit and missfires

corker

I would start by isolating the cylinder that may be misfiring. With the engine off, loosen all the plug wires at the coil pack one-by-one - pull each wire out and put it back in (makes it easier to pull off for testing). Take a test light and connect it to battery negative or a good ground. Start the engine and place the tip of the test light next to the plug wire you are going to pull off the coil pack - with insulated pliers, pull each plug wire one at a time (letting the spark dissipate thru the test light to ground) and listen for a drop in RPM. The cylinder(s) that doesn't have a noticeable drop in RPM is usually the culprit.
Once you isolate the cylinder, start testing from there - bad wire, bad plug, bad cylinder... You can also do a similar test with fuel injectors if you find the ignition circuit is OK. Disconnect injector plug one at a time at each injector and listen for a noticeable RPM drop.