1990 Es 250 Hesitation

[1badmagnum]

I have a 1990 es 250,great running car except when ambient air temperature falls below freezing.

the car hesitates badly,even when engine is at correct operating temperature.

the check engine light has been on for years,the dealer cannot find anything wrong.

I am concedering replacing the o2 sensor or the maf sensor.

any opinions on which one would most likely cause these problems?

last winter I had the same symtoms,but the car runs all summer without any problems whatsoever.

[ColinBarber]

Does it have a MAF sensor? Most Toyota's don't at that age. If it does it will be worth cleaning.

Ideally you need to know why the check light is on. It could be something like the air intake temp. sensor. If that goes faulty the light will come on and the engine will go into fail-safe. For the temp. sensor it will fix the temp to something like 20c and so the ECU will never know how cold it is.