Happy Holidays...
My wife's van has been intermittendly throwing the P0301-cyl #1 misfire code. It's an '02 with 100K miles. I have recently changed the plugs, wires, and ignition coil. Each time the problem returns. I dumped some injector cleaner in seems to help but the code returned. Please help with any suggestions...
Other than the code the only problem is that the engine runs rough during a cold start. Once the engine warms, it runs fine.

 

might be a bad injector?

 

Someone can correct me if I'm wrong but my understanding is that the computer expects a certain amount of crank acceleration when a cylinder fires and if it doesn't see it, it sets this code, in your case, for cylinder #1.
While it usually is electrical in nature, it also can be mechanical. If there is a valve or compression problem, because that cylinder doesn't develop the power that's expected, it can also be the reason this code is set.

 

I would perform a dry and running compression test, as mfahey had mention you could have valve problem.