I have a 2002 Nissan Maxima 6spd with 205,000KM and have been struggling over the last few months with my car. Initially I had problems with P0300 (multiple engine cylinder misfire) and I ended up replacing all of the spark plugs and coils (Non-oem for both). At the same time I had the valve covers from the 6th gen put on. I was also running codes related to an O2 sensor so I went ahead and replaced that. I had been dealing with a high idle (~1000RPM) for some time and found the idle reset procedure through these forums and it took a couple of attempts to get it to stick but I got it to idle properly around 7-800 rpm.

So after all of this the car was running beautifully for about 2 weeks or so, at which point I began having problems with the car shaking while cold out. Additionally, when the engine is cold and I accelerate there is a hesitation of sorts, as though it stutters and then accelerates. Interestingly enough, I also had an after market stereo put in that seems to cut in and out while the engine shakes. I've replaced the battery and had the alternator tested so it isn't a problem with either. I've gotten codes thrown from P0021 (camshaft sensor timing) though I've had those in the past with dirty oil and from what I've read is a fairly common thing.

The mechanic that I had been using couldn't seem to figure it out so I took it to the dealership for a diagnosis. They said that the none of the cylinders were misfiring, and even though they were after market coils they tend to either work completely or not at all. They recommended that I seafoam the car and let it sit for 24 hours with the seafoam in, which I ended up doing myself. Their rationale was that the problems I was getting could be due to a carbon build up. They told me that they had had a few come in with similar issues and this was what worked. I did get quite a bit of smoke from doing it but it doesn't seem to have made any difference whatsoever.

I should mention that prior to me driving it this May it had been sitting parked for around 8 months or so without being driven and the battery was dead. I was able to get the battery to hold a charge and was driving with the battery until I replaced it around a week or two ago. Not sure if this is relevant but thought I'd mention it anyway.

The car has an unrelated issue (I believe) related to the transmission ever since I bought the car. The input shaft bearing rattles a bit and always has but hasn't changed in any way since I've owned the car over the past 2 years.

Anyone have any thoughts?

 

The main thing that pops into my mind is the coils and plugs. I'd replace them with oem coils and ngk platinum plugs. Maximas hate non oem coils.

 

Thanks for the reply. I put in NGK spark plugs, not sure about the brand of the coils. I had thought that it might be the coils too, and the dealership mentioned that it could cause problems. But after bringing it in, they tested all the coils and said that they were all firing properly.

I think I might try replacing the MAF with a 5th gen one and just transfer the thermistor.

 

The shaking is exactly what it does when a coil is bad. I had a shaking engine and no misfire code and I unplugged each coil one by one and found one that made no difference in sound/behavior and then replaced it and it was like a whole new engine. Start it cold, and while it's shaking unplug the coils one by one plugging each one back in afterwards. When you find one that doesn't seem to have an effect then replace it. If they all check out okay by that method then we'll start looking into other things.