Check Engine Light

elhombre

Hey guys,

So last week I started my car in the morning, everything started and sounded normal until I looked at my dash. There was an immediate solid check engine light. The car was idling at about 1100 rpm. Anyways I drove it to work and it seemed completely fine (power and smoothness in the curve were all there just a high idle). I reset the car the light went off and everything went back to normal.

Fast forward a week to today (320 miles driven), I started the car and again got a check engine light upon cold startup with the same high idle when warm. I scanned and got the dreaded P0300 for a random misfire.

Now I have checked for vacuum leaks in the intake track (tightened down all clamps as I installed some post mafs 8 months ago) and check for exhaust leaks (there were some after the cats but I don't think that would code for a p0300). I reset the code and have driven it 50 miles and everything seems normal.

I am wondering if it has to do with the fact I had only a 1/4 tank of gas at the time and didn't give the pump a chance to prime the system to fuel pressure.

Wilson2608

How many miles on the car? Check your spark plugs as well.
Also the fuel pump primes whenever you put electric power to the vehicle. (Aka turning the key on but not engine)

__________________
Stillen G3, z1 Intake Manifold, Stillen Headers, Z1 HFC's, Stillen Catback. 330whp 267 ft- lbs tuned at Z1 motorsports.

elhombre

The car just hit 44k this week. I bought it with 23k on it last year.

Rid3_FaM0uS

cant stress enough looking over the spark plugs. dont ignore the little things. could have a coil pack going bad as well causing a weak spark. i would definitely start there next.

__________________
Always under construction. . .

elhombre

Yeah I think I am just going to change the plugs anyways, I don't think they have been done for the cars life so they could probably use a replacement.

I would just think that at high load/rpm the rpms would break up if there was a coil with weak spark/plug that was no good. Then again electricity does some weird things. haha

Jayhovah

If you search the forums you will find that some members that had this code required clutch/flywheel replacement to correct. I'd speculate that the ECU can trigger this code based on vibration and not necessarily knowledge that the plugs are actually misfiring.

__________________
2013 Gun Metallic Sport - Gamma V3 Twin Turbogized
DIY Gamma V3 TT Install * Jayhovah's Gamma V3 TT Install Pic'Z and Vid'Z * DIY: Washer Reservoir for the Boosted

elhombre

I was actually reading about those occurrences, and after the flywheel was replaced all was normal.

I have also recently found that when I drive my car and then shut it off then (within 30 seconds) turn it back on it makes a clunking noise. The noise doesn't happen any other time ie if I did the same drive then let the car sit for 2 minutes.

I'm not sure it that is related, however I just had my transmission out of the car and inspected the flywheel/clutch and everything looks/works great.

Chuck33079

P0300 is a pain in the ***. Anything can trigger it. I had a crappy Spec clutch that rattled a lot, and that was enough to trick the ecu into thinking it was a misfire.

__________________
2011 MB Touring-Sport-6sp-Nav/GTM TT/FI TT TDX/JTran/Kosmic/Eibach/Hotchkis/SPC/CSF/RPS/SoThatsWhereAllMyMoneyWent

elhombre

Yeah I got the engine light and I was hoping it would be a simple code... Nope I got the shittiest most ambiguous code there is.

Could a post cat exhaust leak or an exhaust rattle cause the code? I have a beluga cat back (y pipe back) and on cold starts it vibrates slightly.

Chuck33079

Could be. My tuner just turned off the P0300 code. If there's a legit misfire, there will be a cylinder associated with it with its own code.

__________________
2011 MB Touring-Sport-6sp-Nav/GTM TT/FI TT TDX/JTran/Kosmic/Eibach/Hotchkis/SPC/CSF/RPS/SoThatsWhereAllMyMoneyWent

elhombre

Exactly.

Other than the code the car drives great (aside from high idle). Still chirps 3rd gear. haha

TreeSemdyZee

Check you oil level. If it is high, this can cause issues.

I had this happen to my car last year and it sent the idle even higher than yours. If I stopped at the store after driving for awhile, then got back in to drive, the engine would idle extremely roughly.

Because I had stupidly overfilled the car, the oil foamed and wreaked major havoc.
I had to completely drain the oil, then refill.

Once I did that, everything was fine.

__________________
Borla S-Type | Motordyne | Z1 (lots) | South Bend | K&N | Nismo/Nismo S-Tune | Eibach | Aerojacket | Fujimara | Spl | ZSpeed Performance | Kenwood-Infinity-Sound Ordnance | Whiteline | Ecutek | Hotchkis | Clazzio | VQ Vortex |Morimoto XB |Dynosty Tune 329.64hp 265.73 ft/lb

elhombre

Thats crazy. haha

You just made me check the oil. It is luckily (or unluckily) right in-between the markers.

Back to the drawing board.

Wilson2608

Another good place to start is to figure out if the car is running rich or lean when throwing the misfire codes. This can elimate some possisbilites depending on rich or lean. Grab a scan tool and look at the short term fuel trims. (Looks up a video on what STFT if you don't already know). Good luck man!

__________________
Stillen G3, z1 Intake Manifold, Stillen Headers, Z1 HFC's, Stillen Catback. 330whp 267 ft- lbs tuned at Z1 motorsports.

mambaZ34

I have the exact same thing happening to my car. I had it checked out by the dealer before I reset the code and everything checked out fine. My exhaust had come loose out of the left hanger but that was an easy fix. Fast forward 3 weeks and I started the car for the first time in a couple of days and the code is back on. I am convinced it might be an exhaust leak or a bad sensor. I tested for vacuum leaks and checks the MAF sensors as well and they all checked out. Maybe a bad O2 sensor?