2003 350Z SES lit - Codes p0300 and p0021

[atomicdog3000]

Hey guys... I'm new here so plz be kind to the n00b.

I have an 03 350Z, (36,000 miles) and my SES light came on recently. I pulled the codes and I'm getting a p0300 and p0021. From reading through the forums I see that the codes =

p0300 = P0300 Random Misfire p0021 = P0021 Intake Valve Timing Control

Since they both occurred at the same time, I'm assuming that the p0300 Random Misfire is a RESULT of the p0021 Intake Valve Timing Control. I wouldn't imagine that I would have more than 1 coil fail at exactly the same time and also have the timing control issue occur simultaneously. So that's my first question, is my logic correct here? If not, does anyone have any insight in to what might be occurring, especially on a car with such low mileage?

Also, I think I understand what the p0300 Random misfire means, but I don't know how the p0021 intake timing control works. I'm assuming that this is some type of variable timing control to maximize efficiency at different speeds, but I don't know what the code usually indicates in terms of a fault. Does a sensor need to be replaced?

The symptoms of the issue are rough idle and a slight but definitely noticeable loss of power while driving. Also, if I accelerate quickly my SES light begins to flash, but it goes back to constantly lit within 10 seconds or so of normal driving.

Also, if I'm posting this to the wrong area and I should be posting only to the 350Z area please let me know.

Any insight on this issue is appreciated!

[Beancooker]

I think your logic is correct.

Next, have you checked the coils? Easiest way I know of to check them, is to unplug the wire leading to the coil. If you notice a difference when unplugging the coil, the coil is good. If there is no difference, that is your bad coil.

What were you doing when you threw the codes? Were you driving normally, or redlining?

I'll see what else I can find out for you.

[atomicdog3000]

beancooker... Thanks for the quick response. That's a great idea for how to check the coils... I'm going to go do that now. I'll keep you posted.

I was driving normally. I was on my way home from work cruising at about 65MPH... I got off of the highway and when I came to a stop I noticed the rough idle. I continued home from there (just a few blocks) and just when I was pulling in to the driveway the SES light came on. Shortly after I pulled the codes and got both p0300 and p0021.

Thanks for your help!

[atomicdog3000]

Ok... so here are the results of the coil test (taking the connector to the coil off while the engine is running to see if it has a negative effect)

Cylinder 1,3,5 (passenger side) = each time I disconnected the wires it had a definite negative effect. As soon as I reconnected them it was better. So they all seem to be working properly.

Cylinder 2 - I had to skip this one in the interest of time... it is buried underneath a bracket that has a connector or some kind of a sensor or solenoid on top of it.

Cylinder 4 - disconnecting this had almost no effect (interestingly though, when I had it disconnected and tried to turn off the car and turn it back on it was much harder to start) - possibly bad

Cylinder 6 - no effect - possibly bad.

So, just to try something, I put a voltmeter on the connectors... one on a good cylinder (3) and one on an apparently bad cylinder (4). On both, I got the same readings - 14.8 volts constant on the white wire with stripe, 150 - 210 mV on the other colored wire, and nothing on the black wire (I'm assuming this is the ground). Unfortunately I wasn't using a good voltmeter so I couldn't record the fluctuations on the second colored wire. It was definitely fluctuating, but too quickly to record with the naked eye on a crappy voltmeter. But just based on what I observed, the good cylinder and the possibly bad cylinder seemed to be receiving the same input from the ECU, but there is no way to really tell.

So, I'm still wondering if those coils are bad, or if they are just firing at the wrong time because of something related the other OBDII error, the Intake Valve Timing Control p0200. Tomorrow I'm going to check the cost of those 2 coils (and the associated plugs, I might as well)... but I'm definitely still looking for ideas if anyone has any. It's a place to start I guess.

It's weird to me that 2 coils would go bad at exactly the same time, and WTF coils shouldn't be going bad with only 36000 miles on the car.

[elwesso]

You can always have a power balance test done at the dealer..... Id see if you could have it done a couple of times to see if results are consistent.

[Beancooker]

There is a similar thread in the Maxima forum, and may help shine some light on your problem.Link to other thread

[atomicdog3000]

Hey guys... thanks for the help. It sounds like a fairly broad range of problems could be causing this issue, and since I'm not totally sure which is causing the other, I'm going to just break down and take it to the dealer for analysis. I'll keep you guys posted.