My 1988 Ranger 2.9 V6 4WD has started to have a massive idle fluctuation at startup. It settle down after a minute or so and runs great after it warms up a bit Atill gets 20 mpg and hums down the road like a champ. I've had it since 1998 and it has boo coo miles on it Done several tune up things to it lately, Not looked into temp sensor. Changed O2 sensor with no help plus MAP sensor and throttle position sensor. Bewildered what is causing the massive idle fluctuation at startup. Must be a sensor Fuel systemand regulator all good but injectors are original.