engine start speed

[joedunlevy]

1996 yukon / 350 vortec. When the engine is first started it turns up to 1500 rpm for a couple of seconds then settles down to 1000 then to 750 ( after it warms up). Is this normal, I thought with computer controlled fuel injected engines the idle speed was fairly constant (fuel air being controlled by the computer) I get a couple of knocks from the engine (when its warm) when it goes to the 1500 prm start speed.

[abqchevyman]

That sounds fairly normal to me. You might have unburnt fuel in the cylinders (i.e. if it turns over 3 times before firing, you would have about 3 shots of unburnt fuel). This would cause a rapid rpm as soon as it fired due to the extra fuel. Once that is gone, it will settle down into the 'cold' idle at about 1200-1000 rpm and then drop down to warm idle.

 

Personally, I wouldn't worry about. The knocks when warm might be lifter knock since the oil has drained from the heads at that point.