you probably have a sticking valve lifter.
take off the valve cover,remove the rockers,take off the intake manifold take out the push rods,then pull out the lifter,if the lifter is mushroomed you may need to get a lifter puller
could be a lifter sticking
Valve lifter could be sticking. Take the valve cover off and start the engine. You can narrow down which one it is. Might Not be sticking and just need adjusting.
Often a sticking lifter is cause by sludge that has built up inside the lifter. If that's the case a good engine cleaner can often help, or even just add a quart of diesel fuel or kerosene to the crankcase and let it idle for a while, but if you do that, don't put any stress on the engine. Then change the oil and run it for about 300 miles and change the oil again. That CAN help some sticking lifters... but don't count on it. Often the only option is to change the lifters and if the camshaft is pitted, you may need to change that too. If you're going that far, check everything and do a complete rebuild.
It is a lifter either sticking or your fuel injectors it is common with these engines... I have a 2001 that ticks at idle and it is a lifter but as soon as I start to accelerate it goes away. It has done this since a year ago when I bought it I wouldn't worry unless it is knocking.
Take a pushrod and push down on the plunger in the lifter. A hydraulic lifter is spring loaded.
This sounds like a hydraulic valve lifter that is dirty, sticking and is not getting enough oil to lubricate the lifter. After the engine warms up and the oil pressure is stable, the lifter begins to get enough oil and quiets down. Try changing your oil and use a lighter weight oil like 10/W/30. After 2500 miles return to your former vescosity oil.
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Insufficient information is given - but it could possibly be a sticking valve lifter that quiets down and the noise goes away after the engine is warm and the oil is circulating.
Valve lash needs adjusting or you have a lifter that is sticking.
2003 v6 90000 miles lifter tap for 3-5 min when i frist start it ? Purchase a can of Seafoam Motor Treatment and follow the directions on the can. This will free the stuck lifter. Seafoam helps liquefy gum and varnish deposits helping to quiet noisy valve lifter