I've finally had to cry "Uncle" and dropped my Mark VIII off at the L/M dealer for diagnosis. After believeing I had my fast idle when hot issue resolved, it's back with a vengeance.
To review, when over about 75 degrees out, (but not when cooler), the idle will gradually go up to 2000 rpm when putting it in Park after driving. If I shut it off then restart it, about half the time the idle will be normal, but after driving it again, it slowly, ('takes about 5 seconds to gradually move from 650 to 2000 rpm), goes back to 2000 rpm at idle.
I thought I'd narrowed it down to a flakey Throttle Position Sensor, because the problem seemed to disappear after I replaced this over a month ago. But soon after, CEL P0122, indicating a flakey TPS, started appearing. I've replaced it twice now, (first was a cheapo, second a Motorcraft), but the light started coming back again. While on vacation two weeks ago, the fast idle also returned.
So far, I've replaced the IAC, IAT, ECT, MAF, TPS, and PCV - all to no avail. Diagnostics says that if P0122 still lights after replacing the TPS, that it's likely a bad PCM - it's conceivable to me this could be the source of the idle problem also, but the fact that it doesn't happen in cooler air causes me to wonder... If the dealer still has problems finding the source, I guess a new PCM is next...
John
http://mark8.org/users/johnaec/Mark_VIII_s.jpg
'97 Mark VIII LSC
'96 T-Bird 4.6L
To review, when over about 75 degrees out, (but not when cooler), the idle will gradually go up to 2000 rpm when putting it in Park after driving. If I shut it off then restart it, about half the time the idle will be normal, but after driving it again, it slowly, ('takes about 5 seconds to gradually move from 650 to 2000 rpm), goes back to 2000 rpm at idle.
I thought I'd narrowed it down to a flakey Throttle Position Sensor, because the problem seemed to disappear after I replaced this over a month ago. But soon after, CEL P0122, indicating a flakey TPS, started appearing. I've replaced it twice now, (first was a cheapo, second a Motorcraft), but the light started coming back again. While on vacation two weeks ago, the fast idle also returned.
So far, I've replaced the IAC, IAT, ECT, MAF, TPS, and PCV - all to no avail. Diagnostics says that if P0122 still lights after replacing the TPS, that it's likely a bad PCM - it's conceivable to me this could be the source of the idle problem also, but the fact that it doesn't happen in cooler air causes me to wonder... If the dealer still has problems finding the source, I guess a new PCM is next...
John
http://mark8.org/users/johnaec/Mark_VIII_s.jpg
'97 Mark VIII LSC
'96 T-Bird 4.6L