Rough idle but at runs good higher speeds ok ,engine misfire codes intermittent

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

need to find out why the misfire bad coil ,wire ,wrong plug gap etc check injectors and fuel presure --what ever is causing misfire is also probably causing problems with transmission shifting

If you have a check engine light the best thing is to read the codes and find out what the problem is. Many shops like Aamco read codes free.

The engine may be misfiring. I had a 2.4L engine that did that and at long last I discovered that the "Coil Cover Housing" needed to be replaced. This is because the coil cover housing has the spark plug wires molded into the plastic as part of its design. For me this caused an intermittent misfire in one of the cylinders.

replace fuel filter, clean fuel injectors.could have bad fuel, do a code scan before buying new parts.faulty egr valve or faulty engine coolant temperature sensor cause engine run poorly.replace spark plugs and wires because if spark plug wires is bad or spark plug and ignition coil is bad that will cause rough idling misfiring and stalling you have dead cylinder not firing properly..

It is hardly ever the spark plug or only the spark plug - generally for some reason there is a weak or lost spark and the reason must be found and rectified by carefully checking and then replacing any components found to be edfective - plug wires, coil, distributor cap, rotor (if fitted), wiring, connections and could conceivably even be the ECU. Perhaps the misfire is due to injector trouble...

Sometimes a fault with persist even after it has been "cured" until the fault code is erased with diagnostic equipment.

p 0300 is random misfires and 0302 is no 2 cylinder misfire
most misfires are from dirty injectors rather than plugs
run a quality injector cleaner and see if there is improvement

Misfire is a common driveability problem that may or may not be easy to diagnose, depending on the cause. A misfiring cylinder in a four-cylinder engine is, pardon the pun, hard to miss. The loss of 25% of the engine's power output is the equivalent of a horse trying to run on three legs. The engine may shake so badly at idle that it causes vibrations that can be felt in the steering wheel and throughout the vehicle. The engine also may be hard to start and may even stall at idle, depending on the accessory load (air conditioning, headlights and electric rear defroster, for example).

When misfire occurs, performance suffers along with fuel economy, emissions and idle quality. And, when a misfiring vehicle is subjected to an emissions test, it will usually fail because of the unusually high levels of hydrocarbons (HC) in the exhaust.

What causes a cylinder to misfire? Basically, it's one of three things: loss of spark; the air/fuel mixture is too far out of balance to ignite; or loss of compression. Loss of spark includes anything that prevents coil voltage from jumping the electrode gap at the end of the spark plug. Causes include worn, fouled or damaged spark plugs, bad spark plug wires or even a cracked distributor cap. A weak coil or excessive rotor gas inside a distributor would affect all cylinders, not just a single cylinder.

"Lean misfire" can occur when the air/fuel mixture is too lean (not enough gasoline in the mixture) to burn. This can be caused by a dirty, clogged or inoperative fuel injector; air leaks; or low fuel pressure because of a weak pump, restricted filter or leaky pressure regulator. Low fuel pressure would affect all cylinders rather than an individual cylinder, as would most air leaks. A leaky EGR valve can also have the same effect as an air leak.

Loss of compression means the cylinder loses most of its air/fuel mixture before it can be ignited. The most likely causes here are a leaky (burned) exhaust valve or a blown head gasket. If two adjacent cylinders are misfiring, it's likely the head gasket between them has failed. Also, if an engine is overheating or losing coolant, it's likely the head gasket is the culprit.

Intermittent misfires are the worst kind to diagnose because the misfire comes and goes depending on engine load or operating conditions. They seem to occur for no apparent reason. The engine may only misfire and run rough when cold but then smooth out as it warms up. Or, it may start and idle fine but then misfire or hesitate when it comes under load. Also, it may run fine most of the time but suddenly misfire or cut out for no apparent reason. Intermittent misfires can be a real challenge to diagnose, so let's start with a steady misfire in one cylinder before moving on to intermittent misfires.

Hope this help.

COULD BE THE ENGINE CONTROL UNIT.
A PROBLEM FOR HONDA.

i have a 2001 chevy z-71 5.3L. I keep getting a random/multiple misfire code for cylinder 1 . I have replaced plugs, wires, coil pack(only on #1 cylinder)., and fuel pump. I still keep getting the cylinder 1 misfire code. I put truck on a scanner and watched the cylinders. # 1 misfires at idle but quickly stops misfiring at around 1000 rpms. you can here the engine miss at idle but truck runs great on road . anyone else ever had this problem?