I have had this problem for about 8 months. I replaced distributor cap and rotor, wires, plugs but still having the problem. I took it to a shop that told me first it was EGR valve but they had cleaned it and that was not the problem. Then the shop said it was a vacuum leak and then they said that was not it. Now they say that I have bad compression in cylinder 4 only 90 pounds when the other 3 are 205 pounds. They said this is due to a bad exhaust valve. They quoted me 400 for labor, 112 for Headset, 86 for Head blots, and 250 for machine shop. I read up a little bit on this and it seems when this happens (if this is in fact what is wrong) that I should get all 4 done at the same time plus have a new timing belt (of course I have an engine that has 2!) and a new water pump. On top of all that I read that when this happens the catalytic converter also goes bad and who knows how much that will be...like I said this has been happening for 8 months...is it possible I have been driving in 3 cylinders for that long?! Any advice on this mess would be great as I still owe 2000 on a car with a blown engine 
Thank you!
Thank you!