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? I think the first two engine codes have
something to do with the oxygen sensor. I hear they are two oxygen sensors.
Just wondering where I should start first? Any help greatly appreciated.
Thanks.

Hi 21 and 25 both refer to oxygen sensor problems. I couldnt find anything on 43 though that would contribute to rough idle when cold.
I would check the obvious first. Damp/loose/weak HT lead/s, Distributor cap contacts (has one or two got arking burn marks) etc. Spark plugs and gaps.
Air filter.....These are all easily checked by eye. Check colour of spark plug to see if its running either rich, lean or normal.
Oily black soot is normally rich, white/grey is normally lean and a nice brown/tan colour should be normal. Check these easy things first.

Based on your mileage, I think you have the beginning stages of an ISC valve going bad.