P0300 SES light blinked in the rain then went off

[vincenzo masiello]

Hi,
My car is a 2008 Grand Prix (3L8), 115K miles, new transmission installed 4 months ago, and overall performance is good and never had a service engine light on before (except when my transmission died).
A couple of days ago, after driving for about 30 mins in heavy rain, my engine started vibrating violently and the service engine came on for a about a minute and then started blinking.
I stopped and turned off the engine for about 30 mins and then restarted and had the same condition starting from solid to blinking. I was 5 miles away from home, so I started driving a mile and then it starts blinking and stop for about an hour until i got home. when the symptoms started, there was a little bit of rubber/plastic burn smell and the visual inspection in the dark wasn’t showing anything…engine heat normal…fluids good…accessory belt good.

when i got home i hooked up my scanner and read P0300 (random misfire).
Today, when the rain stopped, i started the car with the same fault code, and it was normal, so i cleared the error and it did not come back on.
I replaced plugs with NGK’s and AC Delco wires when passed the 100K miles. I use SEAFOAM about once a month to keep the fuel path clean B) and clean the throttle body, air sensors (MAP) and IAC motor whenever I have time (at least twice a year). I put the best synthetic oil myself and replace air filter regularly. I expect that i have a minor vacuum leak because there has always been a little bit of noise even with new belts and cleaned pulleys and replaced tensioner, especially since the performance/power of this huge engine is not the same as when i first bought the car from the dealer years ago.

I was planning on towing it to a local shop tomorrow (after weekend) to have them do a more experienced and advanced diagnosis, but now that it’s acting normally, can I drive it to the mechanic 10 miles away? or can i just use it for a few days and whenever something happens I tow it to the shop? how serious or urgent is this kind of situation is?

I can post videos/photos and answer any questions for i’m a handy electronics engineer and fully understand sensors and electronics. I just don’t have a garage here in northern PA and it is very cold to work outside even though i have a ton of tools.

thank you in advance for any thoughts/advice

Topic

[Richard Kirshy]

Hmmmm…
Miss firing during driving through heavy rain…
This “ there was a little bit of rubber/plastic burn smell is concerning and should be checked out further for faulty wiring or connection.
Another…might try something simple to narrow the possible issues concerning the miss fire.
Spray water on the ignition wires and coil packs and associated connections and see if the issue happens again.

[vincenzo masiello]

thank you nightflyr for the reply. I was worried too about the smell, i just think that it’s either a spark somewhere outside of the engine or that due to misfire, the burning happened in the catalytic converter for a short period of time before i turned it off.

I have an update. yesterday, i started it and was idle for about 10 mins and the light kept off, but this morning after starting this thread, i decided to take the risk and drive it. i drove for less than a mile and the vibration and blinking service light started again. i turned around and left it home.

Now i’m sure that i’ll be towing it to a good shop tomorrow morning because that is a little higher than my knowledge and capabilities and a little too much work when i have two jobs and one car.

i will update here.

It just make me feel so much better if i get guesses and analyses here about the range of possibilities (worst case?) so that i will be mentally prepared to talk to the mechanic tomorrow.

I did a long study for two days online and watched videos and stuff….and came to the conclusion that it shouldn’t be cylinder specific problems (plugs, wires, injectors, ..etc.) but more like a vacuum leak or egr valve or fuel pressure

[vincenzo masiello]

I have a new update…
the mechanic i sent the car to, who is known in my area for being honest and trust worthy, looks to be not as experienced and knowing as I expected him to be.
He called me at the second day that he had the car telling me that all my fluids are full and that i have a misfire that if i ignore would lead to gas/air mixture moving to the catalytic converter to burn there (these are all things i already told him about!!!!), but he knows now that it is two specific cylinders and since i replace plugs and wires a year ago and i have OEM ignition module, that he replaced the coils one by one with a new working coil with no positive result and that he will test the ignition modules.
he mentioned that there is no vacuum leak in my engine what so ever without mentioning what detection method he used!!!
Now, i understand that taking my ignition module out to test it is much easier physical work than taking my six plugs and wires on his behalf and will add to the bill, but shouldn’t he test plugs and wires and vacuum leaks first when there is only P0300??

He finally told me that he is sure that it is not a gas problem but a spark one, so he assured me that whatever it is, that the bill will be much less than what we both expected.

Anyone ever gone through this with a word of advice?

[Author]

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