My 2003 subaru forester idle very rough. if you open the hood and look at the engine it is shaking like its firing on only three cylinders. I need some help.I changed the spark plugs, gas filter, air filter and all the coil packs so far

The firing order for the 2015 Subaru Forester 2.5i is 1-3-2-4. This means that the spark plugs will fire in the following sequence: first cylinder, third cylinder, second cylinder, and fourth cylinder.
The firing order of an engine refers to the sequence in which the spark plugs ignite the fuel in the cylinders. The firing order is determined by the engine's design and is important for ensuring that the engine runs smoothly and efficiently.
In a 4-cylinder engine like the 2015 Subaru Forester 2.5i, the cylinders are typically numbered from left to right, starting at the front of the engine. The firing order for a 4-cylinder engine is typically 1-3-2-4 or 1-2-3-4, with the spark plugs firing in a sequence that alternates between the left and right sides of the engine.

Could be your electronic ignition module

Spark Plugs --change every 3 years?
Front O2 Sensors-replaced at 100,000 miles?
MAF Sensor-cleaned?
Egr System works as it should?
No cylinder misfires?
No Vacuum Leaks anywhere?
No stored codes?

Shall I keep going?

You have to work on all vehicles at least twice a year
& look for problems

Alternator has no ac leakiage
Fuel filter new
Fuel pressure good
Air filter?
Throttle Plate doesn't stick?

Well this could be caused by a number of things. But the most common cause is an "engine miss." You could have 1 cylinder that has stopped firing. This will cause a very rough idle and very possibly shake or shudder whenever you accelerate. Another cause may be a main "vacuum hose could be disconnected" from it's port. Vacuum leaks cause engine shake at idle. Check for loose, cracked, or disconnected vacuum hoses under the hood. The third and least likely cause is a "broken or worn motor mount". If the engine is not securely held down in place by all the motor mounts, it will vibrate excessively and cause a shake at idle. The engine miss and motor mount problems are 2 issues best left to a professional to tackle. But as I said, you could tackle the vacuum leak issue yourself by checking under the hood. Hope this helps, good luck!

Hello...i'm here to help you, but need a bit more information please. Is the check engine light on in your Subaru? If so, do you know what the DTC codes are that caused it to come on? When you say "2 flooding cylinders" does that mean those 2 cylinders are not firing and the spark plugs are wet with gasoline? What 2 cylinders are they? I don't think the problem is ECM related. Reply back and i can give you some suggestions on where and what to troubleshoot.

First step is to access the Engine Control Module (ECM) using diagnostic equipment connected to the data link connector of the car, in order to pull out all Diagnostic Trouble Codes (DTC) memored. Even if engine Malfunction Indicator Lamp (MIL) goes off after engine starting, it's possible to find out temporary DTC codes memored in the ECM. Then you will be full informed about bad components (e.g. bad heated oxygen sensor(s), cylinder(s) misfire(s), bad injector(s), bad ignition coil(s), ... etc). Therefore you will be able to repair & replace bad components and reset the ECM.
In the most cases when you smell something like rotten egg there are bad oxygen sensor(s).

Black smoke means buring rich. Have the vehicle's ECU scanned for codes and do the repair the codes describe. I'm gonna take a stab in the dark and say Mass Air Flow Sensor.(MAF)

It's likely the coil. Subaru issued a TSB (Technical Service Bulletin) on this issue. This is not a recall but you may want to show this to your Subaru mechanic or call Subaru after your repair to try to at least defray some or all of the cost for the repair. The link is below:

Subaru Forester Ignition TSB

First suggestion is go to AutoZone and get the error codes read (for free) -- this'll probably tell you exactly what the problem is.

Charlie

If the timing belt is broken or has lost some teeth then you will get no fire. Some models have an inspection port that you can see the belt through. Have someone try to start engine while you watch timing belt. If belt is stationary or moves in jumps then this is your problem.