Hey guys, been having some problems with my car and i finally got an engine light. Turns out to be PO300(multiple cylinder misfire). Has anyone gotten this before? My car has been stalling out in the middle of the road, rough idle, backfires, and strong unburnt smell of gas.

On my last thread i explained how i cleaned my maf/throttle body, and removed my grounding kit. Also replaced o2 sensor with bosch universal two weeks ago. The problem happened right after the grounding kit removal not the maf/throttle body or o2 sensor which was days before the ground kit. Car stalled and died, will crank but not turn over. Repositioned the oem ground point and it started but ran rough. Now it seems like it wants to stall everytime i drive.

Possible cause that i found from searching are 1.Bad coilpacks(not sure which one) 2.Fuel injectors,....I will pull out the spark plugs soon to see if anyone of em are burnt(replaced them under 8k miles ago.) Anyone have any idea what the problem could be? Car is 03 350z with 80k miles, test pipes-plenum spacer-exhaust... Thanks

 

I also found this on an another forum. Since all this started happening when i took off my plenum could it be that one of my bolts or multiple bolts are loose? I didnt use a torque wrench but all seems to be snug. Im might remove my plenum spacer and tighten everything up to see if that helps first.


''Problem w/PO300 code & rough idle@ cold start..Solved
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I finally solved the problem with the rough idle at cold start. I installed oem plugs and wires a couple of days ago. After installing the parts, I checked one of the intake manifold bolts. To my suprise, it was loose! In fact, all of my intake manifold bolts were loose! I probably wasted money on the plugs/wires because they were fine , except one plug was missing the platinum pad and the gap was off. THE CAR RUNS FINE NOW. I connected the Tech 2 to the car and 0 misfires were detected. So...if anyone has a rough idle @ cold start or the PO 300 code, check the intake manifold bolts. I hope this helps someone.''

 

you answered the question your self with the symptom of unburt gas

= no fire... probally was your spark...

 

You didn't say anything about removing the plenum in your first post - a rather important and critical detail IMO.

You might have damaged the gasket(s) between the plenum and spacer. Loose bolts can definitely leak. If you didn't tighten them in the proper order, the plenum might not be seating properly. If you caught something between the spacer and plenum that could cause a small leak. Get the idea?

Fooling with the plenum is the sure-fire way to start a leak and that can definitely cause a idle problem or CEL.

 

hmm i dont have any gaskets in between the plenum and plenum spacer. WHich one is that? So im assuming a leak can cause a misfire? Ill get to it tonight.

 

Well if you cleaned you'r mass air flow sensor and sprayed directly on the electronics of it you might have damage it, which would cause that code... And if it weren't working right your car will go in to a limp/ rich fuel mode... And the same would go for your electronic throttle body... Your not suppose to spray directly on those items...

 

I thought that too but i drove the car for 3days after cleaning the maf/throttle body and car ran fine. I then removed the plenum for paint along with the grounding kit. Then as soon as i finished that car stalled on the side of the road. Unless of course it takes a while for a bad maf/throttle body to kick in??

I used maf cleaner on the maf sensor and carb cleaner (safe on throttle body) for the throttle body.

 

its safe somewhat, if you spray directly on the electronics you can still cause issues... thats the reason most techs will spray on a rag and wipe... I've seen a few go bad on bmw's and other cars from techs spraying too much on and yes it can take a few days for them to short out depends on how much of it got damaged... but with your issues it does sounds like your mass air flow sensor... or a major vaccum leak that your ecu cant correct, which you would more and likely hear...

 

also I doubt it would be your coil packs.. or spark plugs... or injectors... since if it were one coil pack or one bad plug or one injector clogged you would generally get the code from the cylinder thats missing like 0302 for cyclinder 2.... and the likely hood of two of any of those items failing at the same time is rare specially when you just played with two of the main things that can cause your p0300 code( plenum for vaccum leak and mass air flow sensor for bad sensor)... unless of course your cars ecu can't pickup on which cylinder is failing than yea you could get the p300 code but I don't think thats your case... borrow a sensor from a buddy and also check for vaccum leaks reset your ecu and see if things change...

 

You may actually be right. I took off the plenum and plenum spacer just like this guy and got the same exact problem/code
https://my350z.com/forum/maintenance...o300-code.html

 

thanks a lot dude, ima check for leaks tomorrow. If that doesnt work ima borrow my friends maf/throttle body to see if that helps. Thanks!!!!

 

Well i took off the plenum spacer and tightened everything up. To my suprise i had 3 slots i missed to tightened. I tightened everything up, plenum spacer off. One was stripped so it was loose but i sprayed carb cleaner around it to see if my idle jumps but it didnt so no more leaks i guess. Car drove hard, felt good, and didnt stall. HOwever my idle is still a little rough, its stays around 400rpm? Also im hearing some weird noise out back under my hatch. Its a hissing sound (hisssss....hissssss) lol if that makes sense.

After this the PO300 code is gone, strong gas smell is gone, stalling for now is gone, and the car pulls hard without hesitation. HOwever my idle is still messed up. Its really low at 400rpm and is pretty rough. When the car is cooling down it would go down then jump, then continue to go down. Its not steady.

 

could still be a vacuum leak OR maybe you need to reset the ecu. I'd try the ecu...longshot but maybe.

 

it was another vacuum leak. Everytime i retorque everything the rough idle and car shake seems to get less worse(i lost my torque wrench so i hand tight everything, i will buy a torque wrench by the end of the week). NOw it feels fine, minor idle jumps but only once in a while. My car doesnt feel like it wants to stall and engine light is gone. Only thing that bothers me is one of the slots near the throttle body stripped from me overtightening the bolt. Now that slot is emptly. But i did check and sprayed around it and no leak. HOpefully my car doesnt stall anymore lol.

Thanks everyone!!!