Engine is misfiring?

I have a misfire problem on my 2002 Ford Ranger. For some time the truck has been running rough. The error codes point to misfire in 4, 5, & 6. Also at the same time the AC also stopped working. I though it was the ECU and replaced it. No luck.
All 6 plugs are fine and not fouled. Cables are in working order.
The several shops I have taken it to have had no luck with finding the problem.
Can you point me in the right direction to resolve this.
Thanks

Chk if fuel filter is clogged, maybe incorrectly gapped plugs or faulty. Fault in fuel or electrical systems. Chk emissions system for faulty components. Do a compression test with a gauge. Vacuum leaks at trottle body, intake manifold or vacuum hoses. Hope u fix the problem

You might have a vacuum leak on your right bank since the misfiring cylinders are all on the same side. What is the manifold vacuum reading? Is the compression ok across all cylinders on the right bank.

My 2002 ford ranger, with a 4 cyl engine, is mis-firing. I've replaced the spark plugs. What else, besides the spark plug wires and coil pack, could be causing the problem?

Skip moves from cylinder 5 to 6 to 5 to 6 every time I cut the truck off and recrank it almost. It has new plugs gapped correct, new wires, new coil pack, can install old plug and skip is more fant than with new plug has correct plugs

Found intake leak why wont it have a lean condition

I own a Ford Ranger 2.3L 4cyl with 87,000 miles. At 61,000 miles the engine began misfiring and backfiring at first startup of day, and also missing under load. The dealership replaced the coilpack and plugs which seemed to cure the problem. At 86,000 the truck again began missing ocassionally under load or mediu, m acceleration. It seems to idle fine and no symptoms are evident during rapid acceleration at higher RPMS. I have replaced the air filter and fuel filter which had no effect. Check Engine Light is NOT on. Any ideas would be appreciated!

You might want to replace your plug wires

Just to let everyone know what I found to be the problem. The engine has an aluminum head. As stated in my original post Cloninger Ford of Salisbury had replaced my coil pak and plugs 22,000 miles previously. When I went to remove the four plugs three of them came out without the need of a wrench. The white of the ceramic and the boots were literally covered with combustion carbon which had blown thru the threads of the loose plugs. This caused short circuiting and the misfiring. Evidently the mechanic failed to use a torque wrench and ended up not tightening the plugs sufficiently. I don't know if there is a moral but I ended up paying to fix a problem they created when they initially repaired the vehicle.

I have a 2002 Ford Ranger Edge 3.0 cylinder with 194,658 miles on it. It only gives the engine misfire P0306 code if I let the engine idle for a minute. I have changed the plugs and wires several times since this has started three year ago when I only had 84,000 miles. I have also changed the coil pack but not luck. Again it only misfires if the engine idles. Does anyone have any ideas?

Wow thanks! I just found this site and it is great! Fixed my problem when no one else could!