It runs rough when it idles. The water pump was changed a couple months ago. But it ran great till last Friday. Someone said it was a firing coil.

You read the codes so what were they exactly? That is only half of the issue. You can have codes that are showing up because something else failed. There is no code that says "replace injector"

To run cars need
1. Spark
2. Air
3. Fuel
so check each. Good luck.

Someone gave me one in tbe fall and I tried cleaning out the carburator and it didn't help. I bought a new carburator made for that model on Ebay and it ran like new. Not sure if that's your issue, but that worked for me.

You have two coils on this engine. Test each wire for spark with the engine running. You'll find at least one wire not sparking. replace the coil that has the wire that's not sparking.

it could be a broken or unhooked vacum line but i really am gonna go with the timing being out a couple of teeth it thats the case the car would idle rough and and stumble plus lack a bit of power on take off. if the timing is off the comptuer will compasate for that and advance the firing on the coil the comp uses a few different sencer's to determine when to fire it uses the cam shaft postion scencer and the crankshaft scencer you should have the timing rechecked by a different shop and see what they say for sure but be suer to tell them that you work done on the vechile.

have the head gasket checked,pretty common on these

If the plugs and plug wires were changed start there. Most times out of ten something happened to the wires. Maybe one of them isn't on all the way. I've already bought plug wires and there was a bad one in the bunch. If two or more wires are too close together they could be letting the spark jump from wire to wire. The rough idle you are noticing is most likely a miss in the firing order and a dead cylinder could be your next problem. I do not recommend running the engine like this for long. Start retracing the steps of the last service.

The fuel filter is only about 5 bucks worth of work/material. Most of the time you have to get 3/8 fuel line and clamps and a filter with male adapters and just cut out the old one. But it's still a 20 minute job. Also try some dry gas or fuel treatment. If you change it and it's still acting up I think a Vacuum leak or a weak coil is the culprit. Hope this helps.

Check for bad spark plug wires or wires connected to the wrong cylinder.

Mine did that to me about 4 months ago. I started by changing the fuel filter it ran great for a month. but by doing that it released all the pressure off of the fuel pump which then went out. If you run your vehicle below 1/4 tank it starves the fuel pump. The pump needs that fuel because; The fuel is the lubrication for the pump. Running your tank down consistently over a period of time will short the pump out faster.