2004 Chevy Cavalier Jump/Surge While idling or stopped

Tried putting in a gas treatment. No improvement. Tried spraying the choke cleaner as recommended. Still no improvement. I took the car to my mechanic and their diagnostic read 'Cylinder 4 Misfire'. They suggested I have the plugs/boots replaced. Well, they replaced those today. Car is still doing the same thing. When in park, diagnostic reads that two cylinders are misfiring. When in gear, it still reads the Cyl. 4 misfire. They suggested replacing the coil module. After trying another one on it, still no improvement.

They are going to look more in depth to it in the morning. Any ideas what the culprit may be? The only thing that worries me is not that things cannot be fixed, but that they are going to be insanely expensive. I already have my other car in the same shop and am awaiting a new (used) engine (busted crankshaft, cracked head, and warped valves on the old one) for it. Of course, it's a 96 Neon with over 400K miles on it. Any peace of mind in knowing what may be wrong with the Cavalier would be appreciated.

They are going to start checking it again first thing in the morning. I am to call them at noon and I will ask about the injectors. Stills has me believing that some poor fuel may be the trouble, or some of it.

Thank you so much for your responses!

I went to get my car from the shop today, but still nothing was fixed and now the idle is much worse. It's no longer a subtle annoyance but seems like it's about to stall out when I come to a stop. The mechanic said he believes the timing chain may be stretched, however it will require opening it up a little to check that out.

Regardless, with how it's acting after getting it back and getting to drive it for a little, accelleration is much better than before, however the idling is a lot worse, I am going to take it back to the shop tomorrow and, albeit having to pay a high labor fee, have it checked to see if it's the timing. I'm able to borrow another car, so I hope within the next week (will be a week before my next payday to pay for repairs) they can pinpoint the trouble. I will ask to see if they have checked compression and fuel filter/injectors as well. I am hoping it is not going to be the chain, which is quoted as a $600 repair, but at this point, I just want to know what it is!

I asked today as you suggested. They said the compression was reading 200 across the board, which. Well I suppose that's normal. All injectors are working like new as well. While I was there, the mechanic had me listen to something. You can hear a very, very distinct metallic sound it begins it's rough idle. He said he's about certain it's the timing chain with some slack in it. Think the way a bicycle chain sounds when it's changing gears on a multi-speed bike. It sounded very similar, but at a higher speed of course. Really from all the tests that have been done, there is not a whole lot else that it could be. I'll keep my fingers crossed a loose timing chain is the trouble, but yeah, I definitely heard the sound today when he pointed it out, and my grandfather noted yesterday when he drove it that if you got between 50 and 55, the car drove rough like it had a bad wheel vibration. I asked another former Army mechanic (one I work with) about it, and he said it was possible that chain was the trouble too. If they say it is not the chain after all the work and money I've put in already, I AM seeing about another mechanic if not just biting the bullet and taking it to a dealer.

I would suggest checking out the catalytic converter. My car started acting the same way today. My guess is the dam thing is plugged.

NEWS FLASH. My 99 Cavi was acting the same way. I have changed plugs and wires, fuel filter and cut out converter and put on new muffler. But she still sputters and spits. LOL Must head to insurance company and add fire and theft:)

Did you ever figure out what this was as my cavalier is doing the exact same thing.