At my wits end, codes p0300 p0021. No one can tell me WHAT's WRONG!
 

Okay, I'm not sure what to even do at this point.

I have a 2002 Nissan Maxima SE.

For the past few months my car has had a rough idle and sometimes gets rough when accelerating. Back in August, I went to the Nissan dealer and stupidly paid $99 for a diagnostic. They said they couldn't really tell what was going on because my sparkplugs were bad. They quoted me $700 to get it fixed.

Then, I go a local mech to change them for like $99 (when he was changing them, he noticed an oil leak. Oil spilled into one of the spark plug holes in the back but he cleaned them out). He also told me my valve cover gasket needed to be changed which was causing lot's of oil to seep through and got that changed. Car ran better...but then the check engine light was on again.

So I take it to Meineke and they can't really tell what's going on. The mechanic there said it could be oil related because my oil levels are low....and the filter was dirty. So they changed my oil and reset the engine light.

But it's come back. The car DOES run a lot smoother after the oil change, but sometimes it's a little bit rough. And it's throwing the P0300/P0021. The Meineke guy said he wanted to try the oil change first because it could get expensive.

The problem is that I don't evne know what to do. Even Nissan couldn't pinpoint the problem exactly and I don't want to keep paying people to figure out someting only for them to say ''well, let's try this first''.

p0300 is multiple cylinder misfire. The common problem is bad coils but injectors could be bad as well.

The oil in the spark plug tube is a common defect on 5.5gens with the rear valve cover. The best/cheapest fix has been to replace the cover with a 6th gen but I've recently read posts of those not being as cheap as they used to be. Still the better option though since the tube seal issue was addressed with the 6th gen.

p0021 I believe is pretty common, I've seen it many times myself. I've read many posts that attribute it to low/dirty oil. I replace my camshaft position sensor just to do it and I haven't seen it for awhile.

EDIT: What year is your car and how many miles?

I have a 2004 Maxima and I just went through the same issue. I had one bad coil which was causing the car to only fire on 5 cylinders. I also had to replace both Cam Position Sensors and the EGR valve was stuck. All in all it came out to about $850 for everything.

I went through the same thing though, I replaced the plugs, changed my oil with insane frequency, and started replacing gaskets left and right. It all helped for a little while and then the issues came back.

Fair warning, if you get that done your check engine light will come back on after driving for a few miles. Its the Idle Air Relearn procedure which didn't work for my car. The more I drive it the better my idle gets though. There is a manual procedure you can do once you get your warm idle below 1000 RPM (It works on 6th gens, I don't know if its the same for your car).

Hope this helps!

2002 Nissan Maxima SE 140,000 miles

There is no EGR valve in the 2k2. You got hosed if they say they replaced or fixed it.

This is easy. IVT solenoid is dirty, perhaps bad.

It causes your exact symptoms including random misfire code.

There are lots of threads on this.



And who the F pays 800 for 100 dollars worth of sensors that take 2 mins to swap out? JFC. That's theft!

I have a 6th gen (2004). It most definitely has an EGR Valve.

2k2 max is 5.5 gen not 6th

I'm also aware of that, thank you. I chimed in since this vehicle was exhibiting similar symptoms to my own, and my knowledge of cars is not limited to my specific year or model.

While the EGR valve isn't applicable to this car, the coil packs and cam position sensors are.

Is it something I can fix myself easily with no experience? Or should I get someone else to do it? And how much should it cost? Thanks! :D

This will be short and simple,are you seeing huge amounts of blackish purplish smoke out the tail pipe yes, you have a headgasket issue, oil on the plugs change the plug seals and the rear valve cover changing that won't do much but,if thats bad too,after you did all of this and you still see lots of oil on the plug you have bad oil rings and compression rings,how does the car perform in general loss of power or good in power you feel the torque and power.

I had the p300 code and the leaking valve cover which causes oil to get into the rear #5 plug. Replaced both valve covers with 6th gen parts, replaced spark plugs, and all 6 coils. Car is running like new again. I just recently changed both cam position sensors because I had a pending code stored that never triggered the CEL. There's no point changing plugs or coils until you take care of those valve covers. I went the cheap route on the coils which most don't recommend, but so far so good after 1 year. Only time will tell.
https://maxima.org/forums/5th-genera...ion-coils.html