2003 Toyota Corolla Craziness


I decided to do some routine maintenance on my Corolla about two months ago and unfortunately this maintenance messed it up. I put new spark plugs (Bosch) and a new belt on the car. About a thousand miles later the spark plugs all fouled out and flooded the engine. I was on a two lane road wothout a shoulder and ended up driving about a mile with it shaking and spitting. I had it towed to the dealer and they diagnosed the problem as the plugs (Toyotas don’t like aftermarket plugs apparently) and replaced them. After a week I noticed my mileage had gone down and pulled the plugs and they were all covered in carbon deposits. I bought another set and replaced the O2 sensor. No more nasty plugs but the mileage is still less than stellar. Anyone have an idea what could be causing it?


[b]No Check Engine light?



Check the oil. If it’s really high, change it. You might want to change it anyway. I think that gasoline in the oil should be gone by now, but you had all that other crud in the combustion chambers. Your valves may have huge amounts of deposits too. The catalytic converter may be half plugged.


I think there is something wrong with your engine! Well I should say there was something wrong even before you changed the plugs. I have put plenty of Bosch spark plugs on my previous Corolla with no ill effect. My current Galant has the same plugs. NonOEM plugs could cause minor problems in some cars, but getting fouled that fast has another reason. Have they checked the compression on the cylinders? What was the car doing before you decided to change the plugs?


It had no problems before and the check engine light only came on as the engine started hesitating. The light hasn’t returned since the new plugs were installed

That CEL (check engine light) is just a kid in class waving her hand trying to get you attention because she has the answer. You need to have the codes read. Some places will read them for FREE. Try Autozone or Advanced Auto Parts. Get the exact code not just their translation into English and post it back here. It likely will have a format like P1234.


I don’t have a CEL anymore and since getting new plugs I have reset the computer. So that won’t be much of a help.


The engine is running rich. It’s an open question as to if the oxygen sensor is reporting it to the computer and the computer isn’t correcting the mixture. A complete scan, with an able mind behind it, should reveal the cause. As a stop-gap measure, you could change the coolant temperature sensor. It’s been known to help. There is no substitute for a good scan, or at least, a thorough check with a multimeter. Auto Zone can do a code read, which isn’t really a scan; but, it could reveal any “pending” codes in the computer. They can be present even when the check engine light isn’t on. That is a clean air filter, isn’t it?


One would think if things are this bad that the CEL would illuminate.
You might consider checking the fuel pressure regulator to see if the diaphragm is ruptured.

No black smoke out the back? Runs well/bad until the plugs foul?


No black smoke and no CEL. I don’t want to start replacing components randomly to find out either. The dealership should takes forever and I don’t want to spend a ton of money for another diagnostic to find nothing.