solar_n_orange

Last fall before I put my Z up for the winter the CEL came on and so I had it read and found it to be a P0300 Random Multiple Misfire Code. I'm guessing this was the cause to my idle stuttering and having a slightly sluggish acceleration. I decided not to worry about it because I was going to be parking all winter anyways.

Spring arrives and i finally get a nice day off to get my Z out and the battery is toast. Ok not bad its the original in an 03. So i put in my new battery today. Start the car up and the same code still appears. This evening I went to take my Z back out for a quick spin and it won't start. Apparently the clutch sensor that tells the car its engaged is faulty. Clutch makes full contact but it still won't start. Gotta press it a few times and eventually she'll fire up.

So Long story short I get her started and the CEL is off. Now i only have an ever so slight stutter at idle and she feels much more responsive.

I have absolutely no clue how this seemingly dreaded code can just clear itself. I'm assuming it will come back and have already ordered coil boots as my first attempt at fixing it, but seriously how can it be there even after a battery change and then just randomly disappear?

Mike@Blackline

iTrader: (37)

the code probably cleared bc the car sat with a dead battery for so long. so itll most likely come back

solar_n_orange

This is what I was assuming as well. It was just odd that after installing the new battery the code remained and then just disappeared.

I hope it doesn't come back but I'm sure it will. And then I'll be seeking advice as to how to fix that issue. Can't seem to find any clear cut info on fixing a P0300 code. Just a bunch of trial and error that seems to be different in every case.

solar_n_orange

UPDATE: P0300 code is back. Thought it would come back.

Here is what I've tried thus far to clear it:

1. New Spark Plugs (NGK Laser Platinum)
2. New PCV valve.
3. New belts - didn't think this would help but needed done.
4. Clean MAF
5. Checked all Vacuum lines for leaks - nothing found.

Things I might try:
1. New spark plug boots.
2. Test pipes - have heard dirty CATs can throw this code.
3. Clean throttle body.
4. Start swapping coils around - don't think this will even help at all though.
5. Install a grounding/earthing kit.

Other than that I can't think of anything else to try and clear a Random Multiple misfire code. I suppose it could be a fuel pressure related problem. But I'm guessing electrical. I'm open to just about any suggestion right about now.

solar_n_orange

P0300 code is still present. Today I hooked up my OBD2 scanner and it said I had 2 codes. I was like hot damn maybe a cylinder number to go with the p0300. Nope, apparently its possible to have 2 p0300 codes. And I still can't seem to find the issue. And now I am desperatley searching for help.

Thins I've tried:
1. New plugs - NGK Laser Platinum (gaped according to service manual)
2. New boots - Old ones didnt look bad at all but the new ones had a much better fit.
3. New PCV valve
4. New belts
5. Cleaned MAF.
6. Cleaned Throttle Body.
7. Inspected all vacuum lines on the car. Then took them all off for inspection. No Leaks present.

Things I may try:
1. Pulling all plugs and installing Denso Iridium.
2. Installing Test Pipes.
3. Checking fuel pressure - need advice on how to do this.
4. Installing an earthing kit to help with electrical interference.

The car doesn't have a terrible drop in idle RPMs until it has been driven at temp for around 15 minutes or longer. And today sitting in the drive way reving to around 3500 rpms I noticed it sputtering heavily when i let off the gas. And the exhaust smells absolutely horrid. This is why I'm leaning towards really dirty CATs being the cause. But you would think an O2 sensor would trip if that was the case.

The only other thing i can think of is something being faulty with the Crank Position Sensor or EGR. Although my car doesn't seem to have the symptoms associated with either of those issues. To me it really feels like it just isn't breathing all that well. Like a fat kid with asthma.

I would appreciate any and all suggestions. I really want to get this fixed.

Thanks

solar_n_orange

Would it be a good Idea to check torque setting on spark plugs? I didn't have the Service Manual when I installed them so I went with generic settings off another site. Plugs have been in for around 2000 miles so if they were torqued wrong they may be toast already.

Zazz93

iTrader: (2)

I wouldn't spend a ton of time with the plugs if you've replaced them and had no luck. Torque shouldn't be a big deal provided they are in well and you can get them out (but the proper figure is 18 lbs).

How long was the gas sitting in the tank, and did you use a stabilizer when storing it? When you talk about bad smelling exhaust and sputtering on throttle it leads me to believe the gas in the tank may have caused a problem with the fuel system.

Zazz93

iTrader: (2)

Also try running it long enough to see if you can spot a difference in the plugs. Because the 0300 code is a "Multiple" Cylinder misfire it could be a problem with just two cylinders and is not always truly random. I got that error when I mixed-up the attachment of two coils (cylinders 4 and 6).

solar_n_orange

My typical storage procedure is to run the tank down to around a 1/4 tank of gas before storage. I didn't use a stabilizer because here in Kansas we usually don't have horrible winters and I'm able to get it out once or twice to run it. This year however it sat for 4 months straight.

The problem started last year after changing the plugs and replacing the injen air filter. I'll double check all the harnesses to make sure I have the proper order. I know on the drivers side (not sure of the numbers) the harnesses are a little confusing and maybe i got those crossed.

I'm just worried I tightened the plugs to much and cracked an insulator. I did it old school i guess and hand tightened them and did another 1/4 turn.

solar_n_orange

Just did an ECU Reset, along with the whole Throttle Body and Idle Air Learning and although i still have a rough idle it isn't nearly as bad. Now it only seems to be fluctuating between 600 and 650 RPMs. So for now I'll take it. If the problem worsens I will be replacing the plugs with Autolite-Xp-Iridium. I know there not NGK but these will fit my 07 Camry V6 after a re-gap if it turns out the plugs weren't the issue.

On a side note has anyone tried this little trick form JWT:
http://www.jimwolftechnology.com/wol...BILITY_FIX.PDF

I know its for modified cars but just wondering if it would work to help smooth out the idle?

Edit: Thanks for the tips Zazz

FastWhiteZ

I just did the same thing. How did you get rid of the SES light? Did it turn off on its own, did you reset ECU, unplug the battery? I've tried everything and it still comes back. I just unplugged the battery and will check it in the morning, but if you could give me some tips I would be in your debt!!

Zazz93

iTrader: (2)

If you mean, How to clear the code without a reader, just unplug the battery for about 5-10 minutes. FSM says to pump the brake a few times to ensure the capacitors are fully discharged but I've never had a problem with disconnecting it.

As for the code, if it still occurs check the fuel pressure. If the pressure is erratic, it will cause a misfire. I was running on a pump that was gonna out for the last year or so and wondered why my car's performance was erratic. I just marked it down to IAT's and the computer's adjustments. Now after putting the motor together correctly and with a few more mod's the fuel issue was a little more pronounced. Not long after the rebuild (with cams and ported heads) it began to experience hard starts and that prompted me to swap out the pump. After swapping out the pump it was night and day. Idle got better, still not good but better, and WOT seems +10-20whp... I can't imagine I didn't notice it earlier.

Zazz93

iTrader: (2)

Ohh... I didn't notice your post said, you found the #4 & #6 wires mixed up. If that is the case I'm sure your problem is solved. But watch out for a new one... I also destroyed my Bank 1 cat after doing that. The two cylinders do not fire in tandem so there will be a lot of fuel being sent into cat and if it runs red hot for more than 5-10 minutes they are normally toast.

FastWhiteZ

Thanx for your help. I only ran it like that for about 10-20 seconds. I noticed it idling rough and the SES light on and quickly turned it off. I rechecked and found the swapped wires and fixed them. Would it still mess up the cat or should I not worry about it?

Zazz93

iTrader: (2)

You'll probably be fine, what you want to look for is the cat glowing red from all the unburnt fuel being burnt in the cat's element. You you only ran it for a few minutes you're probably ok. If you drove it around like that it might be damaged but you'll know when the Hp's feel a little funny.

FastWhiteZ

Good to know. I've been worried for a few days and searching here only gave me this thread. So the light will go away on its own?

Zazz93

iTrader: (2)

You would need to unplug the battery for a coulpe of minutes or use a reader to clear the codes. If it comes right back there may be more of a problem.

Zazz93

iTrader: (2)

Hey Solar, I tried that JWT Stability trick when I cam'ed the car and did'nt think it was useful. Did you problem sort out?

blAk mAx

problem solved?

Armitage

iTrader: (15)

Going to follow this one. Had My car up on the dyno for a re-tune today (keep getting a Lean Condition P1283) and after the first run, a P0300 popped up. I haven't noticed a lumpy idle or any hesitation prior to that code being thrown. Being that I haven't done a proper tuneup on the car with it now going on 120k, it's long overdue, so that will come first.