i have an 87 rx. it runs great when the CEL is on. after it warms up the CEL turns off and it runs poorly. it barely idles, stumbles when the accelerator is pushed, seems to miss, and seems to run smoother above 3k rpm. any suggestions?

Could it be a bad coolant temp sensor? It has an aftermarkit temp guage that seems to read ok.

Does anyone know if the ecu & the gauge use seperate coolant temp sensors? The stock temp sensor on the thermostat housing has been replaced with the autometer one for quite a while. Recently, code 21 shows up on the ecu (temp sensor or ciruit). I installed a stock sensor. Now it runs better, but it still shows the same code. Any ideas?

Thanks.