KlausC,

You stated as follow(s): "Check the hidden vacuum elbow next to cyl #1. The hardest to replace and see." I did check this and it is fine, and it should be as its part of the PCV system which was replaced in 2016, so as I stated it should be fine and is. This was proven out in the smoke test and brake cleaner sprayed on said elbow.

So here is what I've done tonight.

- smoked the system and found nothing,

- sprayed brake cleaner on all the injectors and vacuum elbows, nothing.

- measured resistance on new ECT and found the following:
Cool = 1800 Ohms, Hot (boiling water) = 170 Ohms, so this is what I need to compare the current one to, and these values make sense, engine cold, high resistance tells the ECU to dump lots of fuel into the engine, low resistance tells the ECU that the engine is now hot, therefore cut back on the fuel.

And the winner tonight is.... the current ECT Sensor that is in the car as I type.

So I finally checked the resistance on the one in the car. The cold reading was 0 Ohms, dead short, so this tells the ECU, hey the engine is hot, cut the fuel mixture back. So I started the car and let it warm up and then measured again. The hot reading was infinite Ohms, or completely open, therefore this reading is telling the ECU, hey the engine is cold, dump as much fuel into the engine to warm it up so we can reach closed loop mode.

Because of this, the O2 sensor(s) detect more fuel than air in the mixture and set the CEL.

So maybe tomorrow night, maybe Thursday night I'm going to flush the coolant system as its been 2 years since I did it last, and I like to flush both the brakes and the coolant system every 2 years if at all possible so that things continue to run smoothly.

I'll reset the CEL after I'm done, and drive it for a couple of days to see how things are doing.

As far as the O2 sensor goes, I'll put that on my list and hit it at the next oil change.

As always, thank you.

Matt
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1989 - 245, 1990 - 245, 1991 - 245, and 1993 - 245