TwingoJoe94":1ccgp8zp said:
I did say that to the guy who did my service, he cleaned it out with a cotton bud while i held the throttle pedal down, he said it wouldnt be the throttle body, but theres always a possibility. Reason he cleaned it in the first place was because it would only open about 80% of the way, after we had finished cleaning it opened around 85%, so it wasnt going as fast as it should, which is important when your as young as 20. But ill be having a look on the weekend now that youve said that. Thanks.
although i say the thottle body, remember that it's electronic and relies on signal from the unit itself. intermittent faults can cause it to think it's open when it's actually idling so on so forth causing the IAC valve to close resulting in the revs dropping. this doesn't mean that it's an actual cause of the fault, merely a place to begin your investigations.
P0300 is the mother of all missfire codes. choose from 40+ different parts of your fuel, ignition and ECU sensor systems! this means that more than 2 of your cylinders are missfiring.
remember that this problem is something that effects the whole engine
1 - spark plugs.
check that the gap is good. check that all 4 sparks are strong and blue (disengage fuel pump by removing the fuel pump fuse, start engine till it cuts out.) then get wooden tongs hold the spark plug with the wooden tongs on the cylinder head a pubes width above the cylinder head and watch the spark whilst a friend cranks the engine. repeat over 4 cylinders and watch out for any differences over 4 cylinders
note - do not attempt this without dissengaging the fuel pump. otherwise, fuel is going into the engine and out the spark plug hole and BANG!
2 - check for vacuum leaks.
run the engine. do you hear any hissing sounds? if so try and track the problem down, cautiously get some brake cleaner and spray it around PCV / Vacuum hoses one by one ... listen out for a change in RPM, this means that the brake cleaner is being sucked in through a leak and is being combusted as fuel. bingo! also spray it around the intakes of vacuum hoses cautiously.
3. check for fuel pressure.
you may have a fuel pressure regulator that's not maintaning pressure possibly due to a blocked fuel filter or faulty fuel pump. one for the garage to do unfortunately
4. check your battery & alternator.
when a car idles, it's at it's lowest charging rate as this relates directly to RPM. it may be the case that the battery is bad, see here
how/how-check-battery-condition-make-sure-charging-t11916.html although you will want to perform a proper test, testing for CCA. your local motorfactors and halfords will be able to do this for you for close to feck all! my link will only show you charging rate,not battery capacity.
5. map sensor.
the most common cause of P0300 alongside vacuum leaks. google that one yourself lol my fingers are bleeding!