It is an old car but only have 63k on it and never had an issue before. But SES light just came up and I got it scanned, see the picture here:

http://i60.tinypic.com/2jbmb8g.jpg

As you can see there are 3 codes coming all together:

P0300: Random Cylinder misfire
P0507: Idle control system (RPM too high)
P0327: Knock Sensor B1 signal short/low

From what I can reason, it is due to my recent mods and cleaning, I am trying to layout them in sequence:

1. I first change the stock intake to K&N CAI and clean the throttle body about 2 months ago, after a couple of days rough idle and stall, it came back to normal and idle speed is about 650rpm just like before. No SES light.

2. I then added motordyne 5/16 spacer about 1 month ago and changed the spark plugs (still stock plugs), after that the rpm is going up to about 710-720, but I thought it will come back to 650 after ECU learning so I didn't take it serious. Again no SES light.

3. Finally a week ago I do the seafoam through my vacuum line, after which my SES was on. However before I can find a place to scan the code, it went away, just as many others have experienced. So I thought it was ok.

Then just yesterday the SES light up again! Since I just needed to change my CATback so I asked the muffler mechanics scan the code after that catback is done. The car runs fine without any noticeable problem, just the rpm is still around 700rpm and the MPG is lower than before.

I asked him to reset the code cause I though the P0300 could be the leftover of my seafoaming. However can anyone suggest what should I go for next?

Thanks!

 

Ok updates:

I knew the 0507 error could be due to some intake leaking so I opened the hood and retight all the tubes connectors I can reach. Started engine and now it is at 650rpm. However later I found most of the time it is still around 710rpm, when it comes back to 650rpm, the car idles a little rough. I disconnected battery but doesn't seem to help.

I have started the car a few times and the SES hasn't come back yet. But I am feeling they will come back soon.

BTW, a lot of people do the throttle body position reset process but wouldn't disconnecting the battery do the same thing? I guess it just takes ECU some time to relearn, correct?

 

More update:

I use a cigar to do a leaking check on the intake and found that the TB is leaking! For some reason I didn't install the washer properly, it almost fell off. I reinstalled it and now the idle comes back to normal, first at nominal 650 then stable at 600. I thought this could be due to my change of exhaust. Will wait for a few days and see.

 

Idle is supposed to be 650 +/- 50 rpm in stock form. It is normal for it to fluctuate a little.

The mods you did should have had little to do with anything - Seafoam or improper installation is the only possible cause.

Since you have found the TB to be leaking - after proper reinstallation reset the ECU and I bet things will return to normal.

 

Thanks
I am thinking the first two errors should go away, but the 0327 error may still be there cause there are other people who use seafoam also got 0327 error code. Not sure if this can go away by itself or I have to open the intake again to get both sensor and harness replaced! It's PITA!

 

possibly ruined the knock sensor from the chemicals - but only resetting the ECU and waiting will truly tell you

 

Anybody knows where I can find the knock sensor harness? The sensor can be found easily but nowhere I can find the harness. From other boards seems for 0327 most probable culprit is the harness not the sensor.

 

I got mine from Z1 Motorsports: 350Z / G35 VQ35DE Knock Sensor Sub Harness ,and yes mostly it's the harness, it gets baked sitting on top of the engine block in between two banks, causing it to deteriorate over time. If you have been driving with the faulty knock sensor / harness, you will feel power restore after you get it fixed. And a must-do before you get a tune. I couldn't be happier when I fixed mine.

The chemicals added in the engine don't ruin the knock sensor, which sits on the engine block, it's the heat that ruins it, and in most cases it's the harness.

 

Thanks.
I just hate to open up the intake again. Do I have to take off the fuel injector and fuel rail to get access to the sensor and harness connector?

 

Unfortunately yes you have to take the fuel rail and intake runner off to get access to the knock sensor and harness connector, and the fun doesn't stop there - the other end of the harness runs down and around the metal coolant pipe on the passenger side, to connect to a plug you can't get to from the engine bay. It's right above the passenger side cat and I had to crawl under my car to unplug it. It's easier with a lift, you could do it by yourself, as I did, but getting some extra hands will definitely help. It's a lot of work, but to me the restored power and knowing the engine running on healthy timing, with (slightly) improved mpg, totally justify the work. Just my .02.

 

Thanks guys. Will go for it.

 

OK I got some more updates.
After a couple of weeks, the error codes didn't come back. However today I bought a cheap bluetooth OBDII reader and it reads the 0327 error code from ECU.
I tried several times to erase it, but everytime after I start the engine, the error code came back. Yet the dashboard never showed the error.

Should I go ahead and replace the KS harness or should I wait until the error code show up on the dashboard?
Any advice?

 

If P0327 is the only error code you got I doubt it'll ever trigger the SES light on your dash. You might have had It for may years and even passed smog without any issue. if you reset the ECU and it keeps coming back then the KS / harness is out for sure, of course you can replace it and restore your engine's performance and some mpg; however if your car drives fine without obvious loss of power and mpg then I think you should be fine for now, and fix it when you need to get a tune.

 

Thanks. I will go ahead and buy the KS and harness and put them on when I find a free day or two.

BTW, I also doubt if 0327 itself will trigger SES. When I used the OBDII reader, it immediately reported 0327 after engine started, however the dashboard never showed SES even after several start/stop cycles. Actually the first time it was started I also saw the 0507 error as a pending fault. I guess it is because I first erased code, but started car before I fixed the leaking so the ECU saw this code only a couple of times which is not adequate to make it a permanent error. I erased it again and it never came back.

Looks like with a 0327 and a pending 0507, SES won't light up.

 

Got a problem. The harness I bought from Z1 doesn't seem to have the heat shield wrapper as on the original harness, should we find a wrapper to wrap it around? I think it's gonna be melt by the engine heat.

http://tinypic.com/view.php?pic=2ylu4pe&s=8