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Discussion Starter · #1 · (Edited)
Hi, everyone. I am new here. I have been trying for days to figure out the problems on my 97 Taurus GL V6 3.0 with 86,000 Miles. Hope people in this forum can help me.

Problem: First months ago, CEL went on. I check cable connections then truned it off. It had not been on for a long time till 4 weeks ago on expressway. The code reading by AZ is P0303. I change the 1 spark plug (sold by AZ), car back on road OK. Week later I bougth another 5 plugs from O'reilly put them on. car ran fine. 2 weeks ago, CEL blinking on expressway. I took it to Ford dealer and paid them to check ($90). They told me the third and fifth misfiring, need new plug, coil, wire sets with a cost of $570. I take back change all of them myself. 1st start good, CEL not come on, but rough idle happen on 2nd start on parking lot (no CEL). I try to figure out why. After reading, I find 1st plug by AZ was the one for later model Taurus. Changed it same as other 5 (Autolite 764). All gaps checked before put on. 1st start and test run fine. After 15 min driving, I stopped engine 5 min later turned on and left it idling for about 5min, it started to stumbling slightly (lighter than with that 1 wrong plug in). But the CEL went on again. AZ pulled the code P0303 again. I cleaned IAC today and test drive for 15 min. as before, car and engine sounded beautifully, quiet and smooth. 2nd start ok too, drove back ok, then left it in idle then stumble again. Shut off, wait a few min, start again, stumble too. So far no CEL. these are not severe stumble, not normal either.

I read the posts on the internet. but cannot find a my stiuation. Driving no problem, red lights no problem, only warm idle kick off the stumbling. Idle rpm: cold start 1000+ then 800-900; warm strart 900, may cause stumbling. never stumble and stop run yet. Anybody can give me some ideas what to do next? Thank you!

finally, if vacuum leaks, should be only warm time? if engine has problme, why only on idle? I don't have any idea now.

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addition: I took the car out test again. Cold start ok, I drove for 30 min city local drive, 20-45 mph and sveral sotps and red lights. Everything went quite well. Back to my drive way, car sounded smooth, left about 2 min idle no problem, then shut off. About 10 min later I started the car again, engine felt some light stumbling. When driving, the car was felt hesitated to go. dove for a few min no CEL on, but not like when cold start.
 

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Discussion Starter · #2 ·
I'd like to report and share with people here that the problem has been solved. After reading the books and posts. I feel PCV is need to be checked before any other possible things.

Guide by the book, find PCV location. It is in the position. But not tight sit in the hole. It is easy to take out. test the pcv for sucking, it is good. check the rubber grommet it is aged. I bought a new one replaced the old one. PVC sits tight in. The leaking may cause wrong data feeds to PCM. then idel rough. misfire ...... I cannot explain all of these.
For guys with old Taurus GL, please check it. It could cause P0303. I looked the book and it seems no code for PCV. That means even if it cause the misfire, you are not get the code for it. Just change plugs, wire, coil is not solve it. So check it, when the rubber grommet getting old it's not provide air tight flow circle. When you go to a part store find one look like yours. not fooled by year printed on the back. I cannot find my year's and go one with the same shape. I also cleaned MAF sensor, changed air filter. Took the car out drive all afternoon shopping, warm started times. NO Problem!! plus early I changed the plugs, wires and coil. also cleaned IACV. Now the 13 year old car run smooth and quiet. Ready to hand down my teen kid next month.

I am not an auto person, but learned a lot these days. Hope this can help someone with idle problem.
 

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If you have changed plugs, wires and coil, next thing to check would be #3 injector. Try swapping it with another and see if trouble code changes to that cylinder.
 

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if problem is still present try the fuel filter lack of fuel at some of the furthest away injectors may cause a misfire on those cylinders. did that to my dad's focus i think he should replace the coil pack too. replaced the plugs/ wires because of a cylinder 4 misfire and there was still a hesitation problem. went to the fuel filter and there still is hesitation. so i am thinking the coil pack because there 80 bucks for it and he does not want to replace it. oh ya it pick up faster then it did but still hesitates. could also be uneven cylinder compression pressures or abnormally low compression pressures mite want to check that out to. if the fuel filter or vacuum leaks do not work.
 
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