Check the resistance on the coolant temperature sensor. It's a thermistor that changes resistance as the coolant warms up, and one that's out of range will not set a code, but it will cause the cold start/warmup problems you're describing. If you've still got the scanner port in the wiring harness, a scan tool will allow you to monitor the CTS performance. This is a common failure on the fuel injected engines- - - -I've seen it a lot over the past 25 years.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
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