I get a random misfire code when my engine is idling on my 04 isuzu 3.5L...i have changed sparkplugs, check all coils, replaced fuel injectors and still get same error message...what should i check ne

the code is for random misfire, multiple cylinders, as you've replaced the plugs and leads then I would check the coils and the fuel injection

Sounds like you've replaced just about everything except the injectors and done a fuel pressure test.

An intake vacuum leak can cause this as well as other issues, read about it below.
Check Engine Light On, P0300 Random Misfire Code A random misfire means your engine is misfiring, but that the problem is not isolated to one or two cylinders. It is jumping around in a random way from one cylinder to another. A random misfire code usually means the air/fuel mixture is running lean. But the cause might be anything from a hard-to-find vacuum leak to dirty fuel injectors, low fuel pressure, a weak ignition coil, bad plug wires, or compression problems. Even a dirty MAF sensor can cause a lean code and/or misfire to occur. The engine may be stalling because it isn't getting enough throttle opening. The cause is often a problem in the idle air control system. The first thing to check is the intake vacuum with a vacuum gauge. On most vehicles a normal reading is 17 to 21 inches Hg. If the needle is lower, is jumping up and down or steadily dropping, you have a vacuum problem. Look for possible vacuum leaks by checking vacuum hose connections, the throttle body and manifold, and PVC valve and plumbing. An EGR valve that is leaking can also act like a vacuum leak and cause a random misfire. The next thing you should check is the fuel pressure with a gauge. If it is not within specifications (refer to a service manual for specifics because fuel pressure is critical for proper engine performance), the problem may be a weak fuel pump, low voltage to the pump (check the relay and wiring), or obstructions in the fuel line (like a plugged filter). A bad fuel pressure relay can also leak pressure and prevent an otherwise good fuel pump from delivering full pressure to the injectors. Dirty injectors can also restrict fuel delivery and cause a lean fuel condition. Many regular grades of gasoline do not contain adequate levels of detergent to keep the injectors clean. Frequent short trip driving accelerates the buildup of injector deposits. Cleaning the injectors with a good quality fuel tank additive (or having them professionally cleaned) can solve this problem. Look at short term fuel trim (STFT) and long term fuel trim (LTFT) with your AutoTap Express DIY. If the numbers are high, it tells you the engine is running lean

I would start with the inlet manifold gasket, these are know to break down causing vacuum leaks which can cause this issue, also check around engine for other vacuum leaks

change the coils but most likely a bad ecu

REPLACE DISTRIBUTOR CAP AND ROTOR REPLACE SPARK PLUGS AND WIRES IF NOT BEEN CHANGED IN LONG PERIOD OF TIME.CHECK IGNITION TIMING.CHANGE AIR FILTER CLEAN FUEL INJECTORS.IF ENGINE STILL MISFIRE IGNITION COIL IS WEAK OR YOU HAVE LOW CYLINDER COMPRESSION.

Misfire code I'd replace plugs wires buy a used icm

A misfire alarm typically means the coil pack mounted above the sparkplug indicated in the misfire had gone defective.

To test it, swap the coil pack with another cylinder, and see if the misfire goes from #2 to the cylinder you put it on.

If the misfire continues to be on #2, then consider changing the sparkplugs.

I hope this helps.

Explanation: The powertrain control module monitors the crankshaft speed and has detected a misfire condition. Probable cause: 1. Ignition system fault-spark plugs, ignition wires, coil. 2. Vacuum leak 3. injector fault. high or low fuel pressure
Since I just fought with this on a 97 Grand Am. We found 17lbs. gas pressure at high idle. (very low) The car idled fine but would not run when hot. Please, please, please get the gas system checked first. Would have saved me two months of "trying" things. Replacing the fuel pump is expensive and complex. Knowledge about the electric and fuel system a must.