2000 Corolla Misfiring - Toyota Corolla, Chevy Prizm (1998-2008)

hey guys, hopefully you can help me with this problem. My car has been misfiring for a couple weeks now. It didnt throw a CEL till a couple days ago. I had it read at autozone and it came out to be a p0300 multiple/ random misfiring. i was hoping it would tell me what cylinder but no. when it started it was really intermittent and would only do it once a week or so. I changed to spark plugs but it didnt help so i changed them again. I gapped them according to the handbook. Ive reset the ECU. Cleaned the MAF sensor, cleaned the butterfly and intake hoses. Now it does it everyday. It misfires at low rpm and and continues till i get higher in the revs. I dont have a tach so i cant tell what rpms. It seems to go away when i get above 45 or 50 mph. It sucks that i have coil on plug and i cant narrow it down to plug wires or a single coil pack. I have different ideas of what it could be from research and general automotive knowledge such as dirty injectors, TPS, bad coils, IACV, etc. Im saving taking it to have it diagnosed til a last resort. When at WOT it stumbles and the CEL blinks but recovers. Im gonna try to use a multimeter on the coils and injectors to see if they get power and ohm out ok and use some injector cleaner in the tank(maybe it was bad gas that clogged them). But any help would be appretiated. I know some things about cars and engines so ill try to be as helpful as i can to other members on this site as well. Thanks

You can still check it like other systems - read the plugs after you have driven around for a little bit - that is a surefire way to pick up the faulty cylinder(s) if there are many misses. NOID lights on injectors are another way to check the injectors - or go old school and use a screwdriver to audibly listen to each injector.

Could also be a slagged over cat - also throws up a mis-fire CEL on occasion. Worse case - could be VVT-i related issue. If the valve timing actuator is sticking or just plain not work - car would seen it is very low on power, no go at WOT.

You can still check it like other systems - read the plugs after you have driven around for a little bit - that is a surefire way to pick up the faulty cylinder(s) if there are many misses. NOID lights on injectors are another way to check the injectors - or go old school and use a screwdriver to audibly listen to each injector.
Could also be a slagged over cat - also throws up a mis-fire CEL on occasion. Worse case - could be VVT-i related issue. If the valve timing actuator is sticking or just plain not work - car would seen it is very low on power, no go at WOT.

each plug looks the same...like it has been slightly running rich...GOD..i hope its no the VVti

I'd start ruling out the "cheaper" components before I start worrying too much about the VVT-i components. Another possible cause is dead or lazy O2 sensor (the latter will not usually trigger a CEL). If the car has 100K miles or more on the clock - might be a good idea to backprobe the sensor and see what it is really doing. Also make sure there is no obstruction in the air induction system (collapsed or very dirty air filter, kinked or crushed flex piping running to the throttle body) - but you probably already took a peek at that when you cleaning out the TB.

Another possibility is poor engine grounding. When new - not much of a problem, but as the miles and age rolls on, good chance that corrosion has worked its way under those ground points all over the engine. The SFI system is very sensitive to this and sometimes will misfire if chassis ground are not good.

I had cylinders misfiring on a 1999 corolla, and had to change all injectors due to a manufacturing defect (per a TSB).

i cleaned most all of the groundings i could find when i cleaned out the intake hoses and changed the plugs.

Where are some crucial grounding points that i could just double check in case i overlooked some? And wouldnt a bad O2 sensor trigger its own CEL?...but what am i saying, I know better than to rely on that and just check it anyway. Thanks

Just follow the ground points from the negative terminal of the battery - those that you imeediately find should be good enough for now.

A bad O2 sensor would trigger a flag - a lazy O2 sensor may or may not set off a CEL. best way to backprobe the sensor and look at the voltage levels to see if they make sense.

Bikeman982

hey guys, hopefully you can help me with this problem. My car has been misfiring for a couple weeks now. It didnt throw a CEL till a couple days ago. I had it read at autozone and it came out to be a p0300 multiple/ random misfiring. i was hoping it would tell me what cylinder but no. when it started it was really intermittent and would only do it once a week or so. I changed to spark plugs but it didnt help so i changed them again. I gapped them according to the handbook. Ive reset the ECU. Cleaned the MAF sensor, cleaned the butterfly and intake hoses. Now it does it everyday. It misfires at low rpm and and continues till i get higher in the revs. I dont have a tach so i cant tell what rpms. It seems to go away when i get above 45 or 50 mph. It sucks that i have coil on plug and i cant narrow it down to plug wires or a single coil pack. I have different ideas of what it could be from research and general automotive knowledge such as dirty injectors, TPS, bad coils, IACV, etc. Im saving taking it to have it diagnosed til a last resort. When at WOT it stumbles and the CEL blinks but recovers. Im gonna try to use a multimeter on the coils and injectors to see if they get power and ohm out ok and use some injector cleaner in the tank(maybe it was bad gas that clogged them). But any help would be appretiated. I know some things about cars and engines so ill try to be as helpful as i can to other members on this site as well. Thanks

Most likely cause is spark plugs, vacuum leak, ignition timing, compression, or fuel injection system.

I think you have to keep looking at each of these until you find the cause.

injector cleaner helped a bit so im gonna replace the fuel filter..probably crapped up with the 87 sludge they sell for 3 bucks a gallon

Sounds like a plan - remember, your filter filter is INSIDE the gas tank. Major P.I.T.A. to get to and replace. But you can still get to it from an access panel (remove rear seat, right behind driver's seat).

Sounds like a plan - remember, your filter filter is INSIDE the gas tank. Major P.I.T.A. to get to and replace. But you can still get to it from an access panel (remove rear seat, right behind driver's seat).

i went to autozone and they said the filter is a non-seviceable part and comes with the fuel pump assembly...do i have to buy the fuel pump or do you know of anyway around that?

There are two filters that you can get at - there is the outmost "sock" filter that takes care of large debris. Then there is the smaller fuel filter that sits inline with the pressure regulator.

Both can be serviced without resorting to buying a new pump. They probably have it flagged as non-servicable, since it takes a great deal of labor to get at them. The dealership would be the best source to get them - as online and retail aftermarket might not have them or has to be specially ordered.

There are two filters that you can get at - there is the outmost "sock" filter that takes care of large debris. Then there is the smaller fuel filter that sits inline with the pressure regulator.
Both can be serviced without resorting to buying a new pump. They probably have it flagged as non-servicable, since it takes a great deal of labor to get at them. The dealership would be the best source to get them - as online and retail aftermarket might not have them or has to be specially ordered.

thank you so much