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Discussion Starter #1
car : 97 Tbird 4.6L with 113k miles.

symptoms: rough, shaking idle when in D (and park, but more in D), engine sounds like weakly "revving" by itslef at idle, and sounds like a diesel (clack-clack), especially after warmed up. (reminds me a lot of the time when the DPFE sensor went south several yrs ago, but it did threw a CEL then...)
seems 95% fine when when driven, almost like normal, but I did feel less power than usual.
idles almost like normal when engine is cold.
Gas mileage has gone down a lot suddenly!

no check engine light (shall I get autozone to chek anyway?).
plugs/wires are only about 25k old (Motorcraft 2x plat's and m-craft wires).
oil level fine.
fuel filter replaced recently, and a/filter, too.
can't be bad gas, 'cause today got some new gas when almost empty, and still did the rough idle thing.
MAF cleaned about 3 weeks ago.
o2 sensors are still oem.
no weird smells.

recent codes:
within the last 2 years (twice): "bank 1 catalyst: efficiency below threshold"
(never did anything about it, 1st time had code erased, 2nd time went away by itself...the 2nd time was about 7-8 months ago, I think; on both times when the CEL came on, car drove perfectly normal, that's why I never did anything about the code)....could this be it?

what do you guys think this could be...?
Thanks a lot, and pls ask if you need any more info to make a guess.
 

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Faster than Porkchop
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2,037 Posts
Idle Air Control Valve or maybe your cats are bad .
Dont know about the "clack-clack" tho .

not really sure but I tried to help .

Good luck!
 

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Discussion Starter #3
Thanks...I'm wondering about the cat's too...I hope the CEL comes on, so I can know what's up...
 
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