1990 civic engine light problem?

i have a 90 civic dx automatic with 234000 miles on it. when you switch on the car and drive it for a while the CEL comes on. when you switch off the car the CEL goes off. then turn on again the CEL is not there unless you drive it for a while and it comes on again. so its like when the car warms up then the CEL comes on. also i checked the number of red blinks in the ECU and i get 12 short flashes and that means its code 12 which is the egr, but i removed the egr cleaned it but CEL still comes on. anybody who can help me out there would be a great help and would really appreciate. thanks.