IAC PID?
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Tuned
Joined: Jul 2007
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From: So. Cal.
IAC PID?
2000 Expedition 5.4L I was driving and monitoring the IAC. With my foot off the accelerator, most of the time it would read around 46. I think that's percent. It's running ok right now. I think I remember reading it at idle and it read 36.
Now the question. While driving with my foot on the accelerator, most of the time the IAC read in the 90s mostly 99. Does the IAC open all the way when off idle? I just want to know if my high reading is ok.
Thanks for any input in advance.
Now the question. While driving with my foot on the accelerator, most of the time the IAC read in the 90s mostly 99. Does the IAC open all the way when off idle? I just want to know if my high reading is ok.
Thanks for any input in advance.
Hotshot
Joined: Jan 2004
Posts: 19,760
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From: St Louis
Do you have an actual problem or is this just curiosity?
If your foot is on the throttle, we really don't care what the IAC is doing since it has nothing to do until you take your foot off the throttle.
If your foot is on the throttle, we really don't care what the IAC is doing since it has nothing to do until you take your foot off the throttle.
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Tuned
Joined: Jul 2007
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From: So. Cal.
Thanks for your reply. That's what I thought too. I do have an intermittent poor idle quality and stall but I can't get it to do it now. So I thought maybe the extra air at cruise might be causing what seemed like high long term fuel trim. Most of the time on my drive yesterday they were between +10 and +15 I've been working on this thing on and off for over a month and after searching for vacuum leaks in vain I'm about ready to take off the intake manifold to check the gasket.
Fleet Owner
Joined: Apr 2008
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From: 0,0,1
Yes the IAC valve opens fully. It does this so that when you take your foot off the pedal the IAC can throttle down the engine instead of having the RPMs do a crash dive.
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Tuned
Joined: Jul 2007
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From: So. Cal.
Anybody still reading this? Hope so. I got the Expedition to act up today. Just sitting there idling after a cold start (not all the way hot yet) it started to idle poorly when I touched the door lock button. I hooked up the scanner and noticed first that the O2 upstream sensors were both running at about .04volts not going up and down and the loop indicator showed open loop due to fault. Short term fuel trims seemed to go into a fail strategy and slowly both would change the same. Like +3.00 then +4.00. I also noticed that the batt. supply voltage (read by the scanner) was 14.2 volts. No codes set.
When the voltage dropped to 13.7 the O2 sensors started doing what they should and went into closed loop and the fuel trims went back to normal. And then it was running good again. Can't get it to do it again.
I'm thinking maybe the high charging voltage (not too high) confused the PCM. I'll monitor it again when I can start it cold.
Any thoughts?
When the voltage dropped to 13.7 the O2 sensors started doing what they should and went into closed loop and the fuel trims went back to normal. And then it was running good again. Can't get it to do it again.
I'm thinking maybe the high charging voltage (not too high) confused the PCM. I'll monitor it again when I can start it cold.
Any thoughts?
Fleet Owner
Joined: Apr 2008
Posts: 24,316
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From: 0,0,1
14.2 volts is not high, it's in the normal range. As to the rest of the conditions, the truck runs in open loop until it gets up to temperature, then it switches to closed loop. It sounds like all of that worked as it should too.
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Tuned
Joined: Jul 2007
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From: So. Cal.
I wish my scanner would tell me what the fault is that put it in open loop. Just says open loop due to fault.
I just ran it again and the voltage stayed around 14.1 and it ran good. It goes into closed very soon after cold start. I guess those heated O2 sensors make that possible.
Ideas? please.
I just ran it again and the voltage stayed around 14.1 and it ran good. It goes into closed very soon after cold start. I guess those heated O2 sensors make that possible.
Ideas? please.
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Thread Starter
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Tuned
Joined: Jul 2007
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From: So. Cal.
Alloro. May I ask your reasoning for the crank sensor possibility? I ran it again today. The fuel pressure is just fine (33 idling and 42 with pressure regulator vacuum hose off) but it wouldn't act up today. I'll leave the pressure gauge connected and start it again in the morning.
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Tuned
Joined: Jul 2007
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From: So. Cal.
UPDATE. Monitored it again today and it did it when almost up to temperature. Fuel pressure the a little bit higher, maybe 2psi. I figured that was because the vacuum went down a little since it was idling bad. The news is that what made it stop doing it was to turn off the engine and immediately restart. After a short, less than a minute, time it went into closed loop from open loop not open due to fault and smoothed right out after restart. Then couldn't get it to do it again.
Took the connector off of the crank position sensor and found a slight bit of oil in there. Guess I'll replace it and see if it ever happens again.
Wish I knew what to monitor when it's doing it. Every thing I've monitored while it was doing it seemed like it made sense. I don't think there's a way to monitor the crank position sensor unless that's the input for rpm.
Took the connector off of the crank position sensor and found a slight bit of oil in there. Guess I'll replace it and see if it ever happens again.
Wish I knew what to monitor when it's doing it. Every thing I've monitored while it was doing it seemed like it made sense. I don't think there's a way to monitor the crank position sensor unless that's the input for rpm.
Last edited by DaveBB; Jul 19, 2013 at 08:35 AM. Reason: extra word
Thread Starter
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Tuned
Joined: Jul 2007
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From: So. Cal.
UPDATE. Well too bad. The crank sensor didn't fix it. It seems to do it (when it does it) Between the time the system goes into closed loop and before the engine temp is all the way warm. This time it did it long enough to be able to spray some brake cleaner in a vacuum hose tee with the vacuum cap removed. smooths right out when spraying a little in there. Looked at the O2 sensor graph after spraying and the lines stayed steady low same as when it's running bad .04 volts or so.
Then all of a sudden it starts running good again and I can't duplicate the problem.
When I get it to do it again I think I should monitor injector pulse width, IAC and MAF and try to record them to compare. It sure seems like what would happen with intermittent low fuel pressure. I'm beginning to think it may have a PCM problem. It doesn't set any codes right away but over the long term it does set P1131, P1151, P0171 and P0174.
Thanks for any suggestions.
Then all of a sudden it starts running good again and I can't duplicate the problem.
When I get it to do it again I think I should monitor injector pulse width, IAC and MAF and try to record them to compare. It sure seems like what would happen with intermittent low fuel pressure. I'm beginning to think it may have a PCM problem. It doesn't set any codes right away but over the long term it does set P1131, P1151, P0171 and P0174.
Thanks for any suggestions.
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Tuned
Joined: Jul 2007
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From: So. Cal.
UPDATE. It did it again while warming up. This time it didn't stop the bad idle, even all the way warmed up, until I sprayed a very small squirt of brake clean into the vac hose. Then the idle got better, the o2 sensors started reading normal and it went into closed loop. I was monitoring several things and the only one I really have a question about is baro psi. 11.42. That would put me between 6000 and 7000 ft. while I'm at 3500 ft. Right when it went into closed loop the reading momentarily went to 0.030 psi then right back to 11.42.
Any input? Anybody?
Any input? Anybody?
Fleet Owner
Joined: Apr 2008
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From: 0,0,1
Have you tested the fuel pressure yet?