Lifter noise / idle problem?

Hello all! I have a `96 Cougar with the 3.8L V6. I am getting what sounds like valvetrain noise from the number one cylinder. When the engine is cold
there is no noise, the car idles well, and it accelerates amazingly well (or at least better than what you think a car with 217K miles should). Once the engine reaches operating temp, a steady clacking noise that changes tempo with engine speed comes up; it is audible from in the car, and seems louder when I take my foot off the accelerator and let the car coast. Under the hood the noise is constant. Also when the noise is present, idle with the transmission in any gear is slower than when cool, and the engine vibrates. Eventually idle drops to 500 rpm and stays there with the engine shaking the car; my scan tool shows that even at 500 rpm, the computer isn't trying to raise the idle speed at all. Also when the engine is hot and that racket is going on, the car loses a lot of power, just won't accelerate for crap, and slams hard on the 1-2 shift. It feels like it takes twice the amount of accelerator to get the car moving than it does when it's not rattling. If this is from a sticky or collapsed lifter, could one problem lifter be causing all this trouble???
I just bought the car from a guy that picked it up from an auction, so ihave no clue about its service history. All i have done so far was a complete tranny fluid and filter change (about 13 quarts of new fluid).
Any insight at all is appreciated!!!
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Maybe a faulty lifter but since it appears to be heat related, it may be a worn big end rod bearing since as the oil gets hot & thins out, it has less of a cushioning effect on the moving parts.
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Shawn wrote:

Hi Shawn.
I forgot to mention that occasionally the noise would stop on its own, and the car's performance would return. It didn't happen very often tho. Go ahead and make up a "pay attention" sign for me: I should have checked the oil level first thing!! It was low - a fresh quart seems to have fixed everything.
Unfortunately it may all be a moot point now. Had a minor accident (was t-boned at slow speed behind the passenger door) and the insurance company may total the car due to its age, mileage, and prior damage. The adjuster looks at the car tomorrow :( If they want to total the car and the damage is strictly cosmetic, I may keep the thing anyhow.
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Hi- I might suspect an injector. If it is flaking out the engine won't run right. Is the check-engine light on? You might run by AutoZone and ask them to scan for codes - but don't buy anything - just let us know what they find.
PoD

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Paul of Dayton wrote:

Hi Paul.
No check engine light at all here, no codes either. Fortunately I have my own scan tool, I bought it when I had three different cars to take care of. As I posted in my reply to Shawn here, it looks like a low oil level led to lifter trouble. I should have known!! I had a `91 Probe that had fits if the oil got low, even tho the oil pressure gauge showed a healthy reading.
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