I have a problem with random misfires that i cant figure out. I have recently replaced the spark plugs and wires. i somehow think its related to my intake. I had a friend (without my permission) cut the plastic connecting piece that went near the radiator off, leaving a gaping hole on the intake box. He told me it would let more air in. It worked for a while, but now i get rough idles (esp when the ac is on, rpm's are up/down constantly) and sometimes it gets choked up esp when accelerating quickly. take off's are hard as well (have to give it alot of gas, otherwise it'll stall)...any ideas what it is??? The CEL will come on, go off, and come on randomly...
Random Engine Misfires, causing CEL wouldnt pass Inspection
- Thread starter p5pusher
- Start date
Random misfire could be your ignition coils - if they're the originals, they should probably be replaced.
Did your friend cut your intake off before the Mass Airflow Sensor (that little black box in your intake tract)? If that is damaged, it could affect your idling. Is there still an air filter before this piece?
Did your friend cut your intake off before the Mass Airflow Sensor (that little black box in your intake tract)? If that is damaged, it could affect your idling. Is there still an air filter before this piece?
SpecRacer17
Member
- :
- 2003 Black P5
Sounds like the old EGR valve issue that will haunt P5's forever. There is an awesome how to on this site I did just two days ago and cured both the idle issues and CEL. Thing purrs like a kitten again now. It helps to completely remove your battery to get at the 2 12mm bolts holding the EGR valve in place. You're going to have a very sore back, but it's worth it. Or you could just take it to the dealer and shell out about $500 bucks for them to do it.
Other ideas:
1. Inspect the rest of the accordion part of the intake and make sure there are no holes. Holes will let in air downstream of the MAF, messing with the A/F ratio. The accordion piping does develop cracks over time.
2. How far upstream from the MAF was the intake cut? If it was cut upstream of the airbox (I think this is what you described), then it should be more or less ok. I doubt this is the problem, since the car ran ok for a while after this was done.
3. EGR should be checked (and replaced if necessary) for sure, as already mentioned.
4. Might want to check if the MAF wire is dirty. There's a how-to or some thread about that on here somewhere. Search.
5. Get those CELs read and then search on this site.
Report back your progress. Good luck!
1. Inspect the rest of the accordion part of the intake and make sure there are no holes. Holes will let in air downstream of the MAF, messing with the A/F ratio. The accordion piping does develop cracks over time.
2. How far upstream from the MAF was the intake cut? If it was cut upstream of the airbox (I think this is what you described), then it should be more or less ok. I doubt this is the problem, since the car ran ok for a while after this was done.
3. EGR should be checked (and replaced if necessary) for sure, as already mentioned.
4. Might want to check if the MAF wire is dirty. There's a how-to or some thread about that on here somewhere. Search.
5. Get those CELs read and then search on this site.
Report back your progress. Good luck!
I have this same issue. I have been live monitoring this as I drive with a laptop. I get two codes. Often it is just p0421 which is just the "warmup catalyst is below threshold (bank 1)" this can come up all on its own and there seems to be no noticeable driving issues. Then some times it comes paired with the p0300 "random misfire" this never comes up on its own, it is always with p0421. When this happens I get what the original poster described. Shuttering and an over all lack of power.
Thus far I have cleaned the EGR valve, Notice that my air box was no longer connected to the "ram air" tube so I reconnected that and put in a new air filter since mine was DIRTY. Replaced BOTH O2 sensors after cleaning them failed.
Next I will try to swap out my coils and wires with a friend's set off a P5 (he just did the 1.8L coil swap) After that I'm just going to unplug the damn light and ignore it. (not really but it has crossed my mind.)
Thus far I have cleaned the EGR valve, Notice that my air box was no longer connected to the "ram air" tube so I reconnected that and put in a new air filter since mine was DIRTY. Replaced BOTH O2 sensors after cleaning them failed.
Next I will try to swap out my coils and wires with a friend's set off a P5 (he just did the 1.8L coil swap) After that I'm just going to unplug the damn light and ignore it. (not really but it has crossed my mind.)
just got it out the shop, had spark plugs, wires, and coils changed and it ran great, 2 days later after driving it, got a P4021 code, and he told me I needed a new cat converter or pre cat, so i drove it for a while, and code just went away, might investigate if it happens again, but for now im just happy i dont have to spend any more money. I just dropped alot of money at the shop...with those repairs plus new radiator, coolant flush, ac fan, and ac switch..
the p0300 is from a random misfire, usually fix is the ignition coils ( would recommend doing the plugs and wires as well) the p0421 is a faulty cat, which is caused by fuel being dumped (random misfire) so the cat usually goes bad from the p0300. I would suggest after doing the coils, plugs, wires to look into changing out the cat. Alot of shops will just change the cat, but the problem will come back sooner or later if you dont change the rest since the next cat will be dumped as well. hope this helps.
and cleaning the egr valve never hurts, well the car it doesnt hurt, but your back will be sore the next day.
and cleaning the egr valve never hurts, well the car it doesnt hurt, but your back will be sore the next day.
