Hey, I got a 2004 Dodge SX 2.0 manual at 160,000km that I've been wrestling with awhile to get to purrrr again. My car refuses to idle great(at times), start great(at times), or drive great(all the time). Sometimes my neon is hard to start at times but it seems that cold moist weather remedies that. Just about every drive when I'm sitting at a intersection it seems like my idle just keeps dipping lower and lower until the engine is vibrating around 600-800 rpm, and even seems to be a steady decrease. Often times I find myself revving the engine now to no avail to get it back to sit around its regular 1200 rpm range. This doesn't happen every time though, especially when the car has just been driving and is warmed up. The only irregular symptom when I'm driving is the pedal seems to be REALLY touchy even when in gear. I will take my foot off the gas for a few seconds then when I lightly reapply pressure I get a jerk(s). So far I have changed the oil, oil filter, spark-plugs(3rd was burnt), spark-plug wires, alternator belt(was squealing), power-steering belt, air filter, cleaned throttle body, gapped the plugs, single vacuum line that had a sizeable hole. I have managed to get rid of codes such as p0172, p0300, p0303, p0507.

All the codes are gone now with p0172 leaving after I cleaned the throttle plate with cleaner. But I still have the main symptoms described above. I have found though what I believe to be two clues. First I'm thinking about reseating my spark plug tubes on cyl#3-4 since they were both raised although only 3 leaked some oil. And at the very base of my second fuel injector is a huge air leak that makes a high pitched noise when I spray water on it, but nowhere else on the car and not anywhere around the other injectors. I also notice my car's power is inconsistent and the fuel economy never seems to compare with anyone I ask to compare mpg. I managed to find another neon owner and his mileage was around 5.5L/100Km, whereas I cant stop calculating mine at upwards of 17L/100Km. Yikes! Now I'm unsure if I have a great batch of problems of if they are all tied together. Right now I'm planning on replacing the injector seals and taking off the head to reseat my spark plug tubes. Should i do this? Is there something else I should look for? Sorry for the wall of text!