For 9 months I've been trying to track down what could be causing the random misfires - P300 code. On cold, foggy or wet days the "Check engine" light comes on. It acts sluggish on acceleration, making turns & causes quite of bit of hesitation if I drive over 60 mph. It runs great on warm days & the "Check engine" light goes off. Here's a list of things that I have changed in the past 9 months: Spark plugs (A/C Delco), spark plug wires (twice), rotor (twice) (second time I sealed screws and rotor with silicone to prevent condensation from getting inside), cap (twice), coil, coil wire (twice), EGR valve, PCV valve, catalytic converter, alternator, battery, fuel pump, fuel filter (twice), air filter, gas cap and last but not least a professional fuel injectors cleaning done 2 days ago. Mechanic said if that doesn't fix it then I need injectors replaced which for parts & labor will run me $750.00 which I don't have. The vacuum lines and fuel lines were checked out & I was told are fine and aren't leaking anywhere. Today it's cold & it had rained overnight & my 99 Asto is acting sluggish again telling me that the problem isn't fixed. It eventually throw out the code if I continued to drive it. Could it be something else that's not listed above? Like the (upstream) O2 sensor that could make the van act sluggish in cold & wet weather? I would hate to dish out $750.00 for new injectors only to find out it didn't solve the random misfires. Help!!
Before you replace the injectors have them do an injector balance test. Normally wet weather does not effect fuel system. Sounds more like you have a crank or cam sensor acting up.
SOURCE: hesitation, stalling like out of gas
Clogged Catalytic Converter. What happens is as you push down harder on the accelerator you force more gas into the system causing a slightly richer mixture and more exhaust flow is neccessary. The easiest way to look for a clogged cat is when it's dark out take it for a ride causing it perform it's problem look under the vehicle if the cat is literally glowing red hot you either have a clogged cat or an extremely rich fuel mixture.
SOURCE: 95 GMC Jimmy 4.3l W vin rough idle
My problem was solved when I repaired my 4 wd activation dash switch. The switch was contacting on 2WD & 4HI at the same time. The front differential activation is vacuum activated possibly creating a tug of war that didn't actually engage it but drained off vacuum from the engine? A theory at best but stumbbled across it because I knew the switch wasn't working properly I repaired it and low and behold rough idle disappeared and all is good for 3 weeks running.
SOURCE: 2000 Camry 4 cyl 2.2L.
sounds like you have a problem with the spark the coil may be on its
way out or there may be oil in the spark plug holls shorting out the
spark.
your best bet is to pull the leads out 1 at a time and and look down
and check for oil if there is oil there get a new rocker cover gasket.
if no oil refit plug leads loosely and start the car remove one lead at
a time slowly and look at the spark cumming out the end off the lead is
it blue? if so it is ok if it is yellow and dull you have a coil
problem. also check that the spark is only coming out the end of the
lead as it may be coming out the side of the lead and shorting to earth,
you can do this by slowly moving the lead around the top of the spark plug holl and see were the spark is coming from
be carfull no to shock your self as it hearts like hell
good luck
SOURCE: 98 Astro Van,when warm hesitating, stalling
WELL YOU CHANGED ALMOST EVERY THING EXCEPT IGNITION CONTROL MODULE........
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