Toyota Repair: Toyota Previa running rough, blown head gasket, internal combustion

Question
Hello, I have a 94 previa non-supercharged with 214000 miles on it. When I
start it up it runs real rough until normal operating temperature is reached.
Once it it warmed up it runs fine. I have had a engine light on for months but
it was running fine until recently. I tried a code reading, counting the
flashing lights, and came up with the following: 21,25,43. Also during the
light flashing sequence the oil light will flash occassionally. Is this normal?
I have done nothing yet but run a little fuel injector cleaner through it which
didn't help. Could this be a sensor or what? Just wondering where I should
start first?
Thanks.


Answer
These are oxygen sensor malfunction codes, they are probably set by the rough running or engine misfire condition, I think it would be a good idea to have it tested for a blown head gasket or other internal combustion leak, the oil light flashing is not normal and is another issue,have you checked the oil level of the engine as well as the reservoir under the hood?