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Discussion Starter #1
Well, my 1997 T-bird idles,drives, and revs up fine about 95% of the time now that I have the pi intake manifold installed. Other mods are: cotton gauze air cleaner, removed intake restriction,MSD plug wires,new platinum plugs,C&L 73mm maf body, and a cat-back Dynomax exhaust system. The car ran great before the pi intake swap (7.4 sec 0-60). It feels more powerful now, but the pleasure is tempered by a strange periodic idle and low speed misfire. It comes and goes for no apparent reasons I have been able to find. The idle misfire noticably can be felt, and results in a slower rougher idle. Giving it throttle only makes a higher speed miss, but it cleans up at large throttle openings. I can drive city stop and go for miles and miles, then suddenly the next stop will be a light bucking sensation with a noticeable miss through 1500 rpm. A few minutes later it can be all gone. So far, every time I get to my driveway, it's on good behavior and I cannot look for the trouble. I may be forced to field check it. I have put some alky in the tank in case it was water in the gas without a change. I have driven with the egr disconnected without a change (I have put a tube on the egr to vacuum check it as good). The symptoms are as if it is a periodic vacuum leak, but who's ever heard of a vacuum leak coming on periodically? If it were the ignition, it should have misfired at higher rpm's as well as idle and off idle, don't you think? Also, if there is a pi manifold related coolant leak, which I most likely don't have, wouldn't it leak out of the engine as opposed to into a port, since the gaskets are pi-type and completely encircle each port? I have checked most but not all of my vacuum lines without finding anything yet. Anyway, I am stumped again! Can somebody give me some possibles? thanks!
 

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Discussion Starter #2
One more thing : The CEL shows no codes. I can deal with codes, so not getting any is a bugger.
 

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well go by the 3 main places to look...air/ fuel/spark.
if any of thoes are faulty that will cause symptoms you are experiencing.....also, dont leave out the possibility that your timing chain might be too loose.....
but in the end it does sound like an egr problem....you could be having eccessive egr flow due to a stuck valve or faulty dpfe sensor....these problems cause a "stumble" in acceleration and a rough idle.....but again, you would throw a code.....but i know from experience that a dpfe sensor could be on its very last leg before throwing a code.....anyway, thats just my 2 cents.
 

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check you dpfe sensor behind the passenger side head, look at the hoses, if you did a PI intake swap you had to remove that sensor to bolt up the new coolant tube, theres a strong chance that the hoses are dry rotted
 

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Discussion Starter #5
misfire

But I diconnected the egr out of the loop and I still got the misfire ( note: the engine runs cherry at least 95% plus of the time). Also, with engine running, when I pull vacuum on the egr, it doesn't miss the same as when I have that periodic idle misfire that extends thru 1500rpm. The hoses on the dpfe sensor look very good.Last night I was able to get the engine to do the misfire for a minute while idling and restarting the car on the driveway for a half hour of trying. I sprayed a substantial water mist over it while running great as well as when it had the hiccup. No sparks, and no idle change during either condition. The fuel injectors all tic the same. I also unplugged each one alternately, while running, and did not get the same kind of condition. I do not have a fuel pressure gauge, so it is remotely possible the pump falters.That will be the next test. However, what would explain the misfire running clean as rpm's rise 1500 thru 5000?
 
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