I have a 2006 IS350 with 200,000 miles. I have been dealing with a random misfire code for about 6 months now.The car runs fine but you can tell at idle it will misfire and the idle will stumble a bit then go back to normal. I have changed the following parts one after another to see what will fix it:

PCV valve, vapor canister purge solenoid, spark plugs, MAF sensor, all 4 o2 sensor, gas cap, cleaned intake manifold and throttle body.

After each of these things that were changed the CEL would come on about 50 miles after. It took about 200 miles after I changed the o2 sensors for the CEL to come back on. Everytime the CEL comes on it is for random misfire for all cylinders, sometimes just a few cylinders then maybe next time it will be for a few cylinders but not the same cylinders as last time, so it is fairly random. The o2 sensors were the last thing I changed and the light has stayed on since it came back on, its been about 600 miles now but before it would come on and off. It would come on and stay on for a couple hundred miles then go off then after a couple hundreds miles again it will come back on.

I had an intake and header back exhaust on car before and it was fine for about 3 years with no CEL, I since put the stock exhaust and intake back in to see if it would make a difference and it does not.

I was thinking coil packs or injectors could be bad but that doesn't seem possible in my mind since its random and not focused on one cylinder. Am I missing something here or does anyone know what it could be? I am stuck and can not think of what else it can be?

 

When is the last time you changed the spark plugs?

If your scanner has freeze frame check the code. It will let you know which cylinder is missing causing the MIL light to illuminate. From there say if it's for cylinder 2 swap the coil pack to any other cylinder. Then reset the code, and see if either the code stays, or moved to the swapped cylinder.

 

Does anyone know if if I can use a multi meter to check the injectors and coil pack to see if they are still good? What is the standard working ohm number that the injectors and coil pack should be at if working properly?

 

It may be worth adding a good quality petrol system cleaner ( injector cleaner ) to the gas tank and running it for a hundred miles or so to see if it has the desired effect.

Has worked for me in the past when I had a low level random misfire.

Dec.

 

I just put in a bottle of chevron techron after I changed the o2 sensors. Did not help me. I also use seafoam every time I change oil as well.

 

Does the car feel like it still has power? I also fought the random cylinder misfire and it turned out to be a bad cat. Do you have access to an obd2 device that will let you watch your fuel trims? It should be obvious if you have an injector problem. I went and checked a couple coil packs, I can do the injectors later if you really want.

Looking at the coil right side up.
[1-2-3-4]
1 -2 ~350
1-4 and 2-4 ~34k
3 was pretty much open, I had nothing to 1 and 2 and 6m to 4.

If you want to get new coils, I got a set off of ebay with like 40k on them for 50-60 bucks. I have an entire spare set, if you just need one or two give me your address and i can just mail them to you around my work schedule.

 

D i c kH, that is the exception there. It's pretty rare a coil opens as most fail under load when hot by way arc over or shorting internally so the spark is there but not being delivered to the plug. These will always bench test fine for ohms but fail for break down voltage or specifically dielectric withstand voltage.

That said, complete open will never fire and will not produce a random misfire code. It will produce a solid P030X after 300 crankshaft revolutions or sooner when the ECU detects an open from that coil pack which should also produce a different code than P030X.

Kind of you to offer coils man!!