Idle changed after maintenance
10-09-2017, 01:05 PM
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Idle changed after maintenance
Hi everybody. Forgive me if I don't make sense, I'm a fledgling home mechanic/enthusiast; I'll try to be extremely thorough. If I use the wrong terminology or phrasing let me know! I'm here to learn. So here goes:
A friend and I replaced the serpentine belt on my 1997 f150 (4.6L V8) because I discovered a split running the whole length of the belt and figured that didn't seem like a great thing! I've owned the truck now for just a couple weeks. I previously owned a 2000 expedition (5.4L) and loved it but needed a "truck" truck. Already I know some things are different between the two engine-wise, so I'm still having an adjustment period getting used to the feel.
So the thing I'm wondering about is that prior to changing the belt I would generally notice the truck idling around 1000rpm or better in park, 800rpm or better in gear, which seemed high? Maybe not, new truck, still learning. However, after changing the belt it seems like about 750rpm in park and 550-600rpm in gear. I did have a code register after the work, but there was a loose hose which I put back in place (removed air intake for more working room) and now it's running really smooth, just lower rpm at idle. Any reason or explanation for this?? Thanks so much in advance for any helping replies! Looking forward to being part of the community!
A friend and I replaced the serpentine belt on my 1997 f150 (4.6L V8) because I discovered a split running the whole length of the belt and figured that didn't seem like a great thing! I've owned the truck now for just a couple weeks. I previously owned a 2000 expedition (5.4L) and loved it but needed a "truck" truck. Already I know some things are different between the two engine-wise, so I'm still having an adjustment period getting used to the feel.
So the thing I'm wondering about is that prior to changing the belt I would generally notice the truck idling around 1000rpm or better in park, 800rpm or better in gear, which seemed high? Maybe not, new truck, still learning. However, after changing the belt it seems like about 750rpm in park and 550-600rpm in gear. I did have a code register after the work, but there was a loose hose which I put back in place (removed air intake for more working room) and now it's running really smooth, just lower rpm at idle. Any reason or explanation for this?? Thanks so much in advance for any helping replies! Looking forward to being part of the community!
10-09-2017, 01:12 PM
#2
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Warm idle should 730 RPM and never flinch. Between 700-750 is good according to Ford. But when everything is right, they idle about right in middle o that 725/730.
800 and 1000 is far out of spec and is usually caused by an unmetered air leak.
800 and 1000 is far out of spec and is usually caused by an unmetered air leak.
10-09-2017, 01:23 PM
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Thanks so much for the response! Again sorry if this is a stupid question, but could the worn belt have had anything to do with the high idle? As we speak I'm sitting in the truck at it's right where you said it should be... It seems to have been evening out over the last couple days.
10-09-2017, 02:11 PM
#4
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Nah, warm idle in park is PCM controlled, you had a leak in the air box assembly connections most likley. PCM is the executive, but unmetered leaks and IAC can deflect it. Load can drop it lower temporarily if you loose the AC settings. This is why when you reset the PCM, you do so with the AC on or in a defrost mode. That's not even required as the adaptive will eventually catch up...with time.
In short, - either the way it was connected to the throttle body (a little off) or the assembly was leaking elsewhere and you fixed it...accidentally lol.
In short, - either the way it was connected to the throttle body (a little off) or the assembly was leaking elsewhere and you fixed it...accidentally lol.
10-09-2017, 02:15 PM
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Did you unhook the battery? Might have been just re-learning.
10-09-2017, 02:15 PM
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Nah, warm idle in park is PCM controlled, you had a leak in the air box assembly connections most likley. PCM is the executive, but unmetered leaks and IAC can deflect it. Load can drop it lower temporarily if you loose the AC settings. This is why when you reset the PCM, you do so with the AC on or in a defrost mode. That's not even required as the adaptive will eventually catch up...with time.
In short, - either the way it was connected to the throttle body (a little off) or the assembly was leaking elsewhere and you fixed it...accidentally lol.
In short, - either the way it was connected to the throttle body (a little off) or the assembly was leaking elsewhere and you fixed it...accidentally lol.
10-09-2017, 02:22 PM
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I actually did unhook the battery cable to replace the terminal, but I didn't have any issues until a couple days later when we replaced the serpentine belt so I didn't connect those two events... But good to know that's something to be aware of, too! Thank you!!
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10-09-2017, 02:37 PM
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My Expedition idles funny for a bit after the battery has been hooked back up. So does my 89 Mustang. I know for a fact the old EEC-IV's had a relearn process. I am assuming the OBD-II ECU's do as well.
10-09-2017, 02:46 PM
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Ok good to know! Like I said all seems well as far as everything running nicely now. CEL is still on so I assume I need to clear it. Awesome info, thanks to everybody!
