Car hesitates and runs rough at low RPM's....worse when the air is on. I replaced the plugs and wires. Could it be a vacuum problem? If so, where can I find a detailed vacuum diagram? Someone also suggested replacing the ignition coil....does this make sense?

I would be looking for a vacuum leak. Check that none of the hoses have been split or disconnected when you were working on it before.

PROBLEM TROUBLE AREA
Rough idle, stalls or
hesitate on acceleration :
.Spark plug faulty
. High-tension cords faulty
Ignition problems:
• Ignition coil
• Igniter
• Distributor
. Incorrect ignition timing
Vacuum leaks:
. PCV valve and line.. .
. EGR line..
. Intake manifold.
• Throttle body
• ISC valve
• Brake booster line

• Throttle body
• Brake booster line
. Incorrect idle speed
. Reset timing
. Adjust valve clearance
. Check fuel system . Check air cleaner
. Incorrect valve clearance
. EFI system problems
. Low compression

Misfire, a misfire is when you have a low cyclinder contribution this can be from a coil pack not firing to a open injector that is not atomizing the fuel in the combustion chamber to a large vacuum leak that is affecting that paticular cylinder.so you have a misfire. High HC (hydrocarbons) fuel not being burnt.2 misfire that concern does the vehicle rough idle smoothes out at higher RPM? If this does check the EGR it simple car running rough at idle feel the EGR is it hot to touch ? Then the EGR vavle got stuck open. another way is pulling out a spark plug wire and checking spark this will determine if the coil is working for that particular cylinder if you do this you need to make sure you dont break the plug wire you will have to wait for the engine to cool down and loosen the plug wire out of the sparkplugs and get it ready for a engine running test.

Clean the throttle body. Check the mass air flow sensor for corrosion of the wire harness connector.

Do a in-take vacuum test, should have 21" of vacuum, if you don't bad cat.

Your cat should last quite a while now it is replaced. I recommend testing coil packs and module. Change plugs and wires and double check your vacuum hoses.

Faulty idle air control valve or timing chain has jumped. So after you changed plugs it got worse? Better double check to see if the wires are right. You should also look for more damaged loose or cracked vacuum lines. Wiggle them all around with the engine running.

change plug and wire if its been a while most cars have 90000 miles platinum plugs in them.but the wires wear before plugs.so change plugs and wires.+clean fuel injectors .change fuel filter and air filter.if car still run rough your idling to low.have idling check .

put some plug wires on the car.

i have had the same problem..and these engine are supposed to b a very low idle (around) 300rpms. check your vacuum lines on the engine there is a plastic tee on the top of the motor which usually dry rots and will have a hairline crack in it and replace if needed