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  #1  
Old 12-05-2014
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"Floating" idle

1999 Ford Ranger 3.0

I love my truck. I love it so much that to improve the electrical system, yesterday I removed a bunch of ground wires and sanded and cleaned the contact points to remove corrosion and improve electrical flow. I noticed my volt gauge was reading a little higher, and according to my cig lighter voltmeter, about 0.5 V increase. Great!

Except part of that process involves removing the battery. So of course, the ECU is reset and needs to "relearn". Usually ECUs adjust fairly quick, after only about 10 to 20 minutes of city driving. Well, it didn't use to do this before i removed the battery, but now whenever im driving, with the truck fully warmed up, if i pop the clutch in to shift gears, the RPMs "float" rather than drop. For example, lets say im shifting from first to second at 3k rpm. The rpms in 2nd gear will be about 1900 or so. But the tach needle just slowly drops to about 2700 and by that point im already in the next gear, making it kinda jerky. Here is a better example: When im driving if i push the clutch in and stop, the idle hangs at 1500 rpm for a few seconds, then quickly drops to about 900 and settles down from there, almost like the engine isn't warmed up completely. According to my obd2 reader, coolant after tonights driving was at 88 Celcius, and that's about normal. I really don't like this high "floating" idle.

Another example is if im in 3rd at 2000 rpm and i go for fourth gear, (which would put it at about 1500 rpm), the engine "hangs" at 2k rpm until i release the clutch in 4th, where it jumps down where it should be. Note that i don't feather the throttle between shifts. I can get a video if needed.

I also uncovered this data from my obd2 scanner, with truck fully warmed up:
(just idling with feet not touching pedals and just the heater turned on softly)
TPS: 16.86%
MAF: roughly 5 or so
Calculated load: 24.7%

IDK what to do. Maybe the ecu is still learning? But i put about 2 hours of seat time in tonight with my delivery job and it continues to annoy me.
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Old 12-05-2014
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Well it is actually suppose to do that.
To lower emissions on manuals while driving the RPMs should remain where they are for a few seconds when the clutch is in, to allow shifting, if you leave the clutch in RPMs will fall to about 1,200-1,500 and then hang there until speedometer drops below 5MPH, then it will start to drop to target idle RPMs.

I know later models do this but not sure on the '99

The fact it didn't do it before would mean something was wrong before and now it is fixed, lol.

Yes, TPS should show 15-17% at idle, 78-82% wide open, this is learn so anywhere close to these numbers is fine.

Yes, MAF should show .5-.7volts at idle, above 3.5volts wide open

Yes, Calculated load at idle looks about right at 25%, it isn't an actual "load" like going up a hill or pulling a trailer.

Last edited by RonD; 12-05-2014 at 11:14 PM.
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  #3  
Old 12-05-2014
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Quote:
Originally Posted by RonD View Post
Well it is actually suppose to do that.
To lower emissions on manuals while driving the RPMs should remain where they are for a few seconds when the clutch is in, to allow shifting, if you leave the clutch in RPMs will fall to about 1,200-1,500 and then hang there until speedometer drops below 5MPH, then it will start to drop to target idle RPMs.

I know later models do this but not sure on the '99

The fact it didn't do it before would mean something was wrong before and now it is fixed, lol.

Yes, TPS should show 15-17% at idle, 78-82% wide open, this is learn so anywhere close to these numbers is fine.

Yes, MAF should show .5-.7volts at idle, above 3.5volts wide open

Yes, Calculated load at idle looks about right at 25%, it isn't an actual "load" like going up a hill or pulling a trailer.
well none of my other cars ever did this. it doesn't feel right. when i push in the clutch on my other two cars the revs drop appropriately, to about 1100 rpm like you said when im coasting, and then when i stop it drops to 800. the ranger used to behave the sameway. i want that way back.

Why does that lower emissions?

also, when im sitting still in neutral if its idling and i punch the gas to rev to, say, 1800 revs, it "floats", then drops. It used to just drop, and it made nasty popping noises that i love (no muffler).
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Old 12-06-2014
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Dropping and then raising RPMs lowers MPG and increases emissions, so if there is no reason to do so it doesn't drop RPMs instantly, hence the higher idle until you are below 5MPH.

But if you feel this isn't correct for your vehicle then I would check two things.
Throttle and cruise control cables, make sure they are not keeping throttle from closing all the way when gas pedal is released.
You could put a temporary spring to pull throttle plate closed, and drive it that way, if RPMs drop as you believe they should then either cables are sticking or factory throttle plate spring is broken or worn out.
Cruise control cable operates by vacuum, when RPMs are high and throttle plate is closed(foot off the gas) vacuum is very high, if there was a leak in the cruise solenoid this could hold throttle open a bit, disconnect cruise control cable from throttle linkage and test drive.

IAC Valve, this is what computer uses to hold RPMs higher.
With engine warmed up and idling, disconnect IAC Valve's wires, idle should drop to about 500rpms, or engine may even stall, either is OK and means no vacuum leak.
Leave IAC disconnected and drive truck, see if RPMs drop during shifts, be careful engine can/will stall, CEL will come on.
If RPMs drop, they should, then you will know the computer is keeping the RPMs higher, via the IAC Valve.
IAC valve is a Stepper Motor, it has over 100 "steps" the computer can set via a voltage pulse, like a Morse code using voltage pulses, that's what the computer "learns" after a reboot, a 'step' is a preset degree on the motor, so 'step 1' might be 001deg, 'step 10' might be 030deg, computer can then send one pulse to get motor(and valve) to a preset location.
Say it uses 'step 20' for warm idle and 'step 30' for cold idle, if idle for its "target" rpm is too high or low it changes it and remembers it.
Now generally if RPMs are not responding to IAC Valve changes the computer will set a code, since you don't have an IAC Valve problem code, I would suspect the problem is mechanical OR there is no problem, the computer thinks this is the way it is suppose to operate.
I have read posts that people have taken in their vehicles to have new software uploaded that removed this high idle "problem".

Since the majority of later model Rangers sold had automatics this just doesn't come up that often but it does come up.

Last edited by RonD; 12-06-2014 at 11:59 AM.
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  #5  
Old 12-06-2014
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Quote:
Originally Posted by RonD View Post
Dropping and then raising RPMs lowers MPG and increases emissions, so if there is no reason to do so it doesn't drop RPMs instantly, hence the higher idle until you are below 5MPH.

But if you feel this isn't correct for your vehicle then I would check two things.
Throttle and cruise control cables, make sure they are not keeping throttle from closing all the way when gas pedal is released.
You could put a temporary spring to pull throttle plate closed, and drive it that way, if RPMs drop as you believe they should then either cables are sticking or factory throttle plate spring is broken or worn out.
Cruise control cable operates by vacuum, when RPMs are high and throttle plate is closed(foot off the gas) vacuum is very high, if there was a leak in the cruise solenoid this could hold throttle open a bit, disconnect cruise control cable from throttle linkage and test drive.

IAC Valve, this is what computer uses to hold RPMs higher.
With engine warmed up and idling, disconnect IAC Valve's wires, idle should drop to about 500rpms, or engine may even stall, either is OK and means no vacuum leak.
Leave IAC disconnected and drive truck, see if RPMs drop during shifts, be careful engine can/will stall, CEL will come on.
If RPMs drop, they should, then you will know the computer is keeping the RPMs higher, via the IAC Valve.
IAC valve is a Stepper Motor, it has over 100 "steps" the computer can set via a voltage pulse, like a Morse code using voltage pulses, that's what the computer "learns" after a reboot, a 'step' is a preset degree on the motor, so 'step 1' might be 001deg, 'step 10' might be 030deg, computer can then send one pulse to get motor(and valve) to a preset location.
Say it uses 'step 20' for warm idle and 'step 30' for cold idle, if idle for its "target" rpm is too high or low it changes it and remembers it.
Now generally if RPMs are not responding to IAC Valve changes the computer will set a code, since you don't have an IAC Valve problem code, I would suspect the problem is mechanical OR there is no problem, the computer thinks this is the way it is suppose to operate.
I have read posts that people have taken in their vehicles to have new software uploaded that removed this high idle "problem".

Since the majority of later model Rangers sold had automatics this just doesn't come up that often but it does come up.
Thanks! I will definitely retry this! Then i will pull the ECU fuse if nothing else changes, to reset the ECU (rather than removing battery cable, which resets the stereo/clock
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  #6  
Old 12-06-2014
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On a related note, why does Fuel Sys 1 evenually go to CL status (closed loop?) upon warmup, but Fuel Sys 2 always stays O (Open Loop)?
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Old 12-06-2014
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Originally Posted by 420stackz View Post
Thanks! I will definitely retry this! Then i will pull the ECU fuse if nothing else changes, to reset the ECU (rather than removing battery cable, which resets the stereo/clock
I unplugged the iacv at 87 Celcius on the coolant temp, fully warmed engine. No change in idle. it sits at ~800 rpm. im about to drive it now. However, when i rev in neutral, the rpms drop as they did before. Does this mean the computer hasn't relearned yet?
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Old 12-06-2014
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Okay. instantly i noticed a change in driving behaviour. it seemed as though i had installed a lightweight flywheel every time i shifted gears. it was doing the effect i wanted, but way too drastically, making gear shifts jerky and clunky. revving in neutral netted the same effects as it did before this whole mess started, revs rise, then fall with popping exhaust noises. I plugged the iacv back in with the engine running and instantly the revs shot up, i would imagine to about 1500 by my ear, held there, and then fizzled down to 800. its back to its old tricks again with the "hanging" idle between gear shifts.
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Old 12-06-2014
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You have an issue with IAC Valve or Vacuum leak if RPMs stay high when IAC is unplugged.

The point of the IAC Valve is computer controlled idle RPMs, this means with IAC closed all the way idle should be lower than lowest RPM wanted, 500 is usual but it can be lower and engine may stall.
If it is staying at 800 then there is a problem for sure, manual trans idle should be 650-700 in any case
Automatics use 750-800

If possible remove IAC from intake, leave wire connected, and turn on key, IAC should open all the way, now unplug wire, IAC should close all the way.
This is just to make sure it can close all the way, if not then that could be causing higher idle and delay in idle dropping.
Clean it and see if you can get it to close.
Also make sure vent on the back side is clean, that allows valve to open and close without having air trapped behind it.
The IAC valve's engine air passages are on either side of the throttle plate.

If it is closing then put it back on and leave wires disconnected, and remove vacuum line from intake manifold one at a time and block the port, when idle drops you found the leak
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Old 12-06-2014
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im saying, that BEFORE i unplugged the battery and cleaned the grounds everything functioned fine. i got a lean code when i bought the truck, but its not a vacuum leak because i used my obd2 reader to monitor fuel trims and figuredout it was the map sensor. i cleaned that, reset the code, and the CEL never came back. im saying its not like the iacv mysteriously failed while the engine was off and the battery was out while i was cleaning the ground wires. this doesnt make sense
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Old 12-06-2014
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Occam's Razor paraphrased: the simplest solution to a problem is probably the correct solution.
Sherlock Holmes solutions, paraphrased: when you have removed all other possible solutions whatever is left, no matter how improbable, is the solution

You are asking, "what could change if all I did was check and clean the Grounds", nothing could change, so that wouldn't be what caused the problem.
BUT...........you could have disturbed other wires??, not grounds

Rebooting the computer wouldn't cause a problem either..........unless the computer already had the problem and cutting power to it caused the problem to surface.
Like the battery back up in that clock/radio......you didn't know the battery has been dead for over a year until the power goes out overnight and you don't get the alarm in the morning, lol, late for work.
Problem was there for a year, just didn't surface until the power went out.

That is what you have, cleaning grounds and rebooting computer shouldn't have any effect of RPM's like you describe, so....................

Last edited by RonD; 12-06-2014 at 09:39 PM.
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Old 12-06-2014
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Quote:
Originally Posted by RonD View Post
If it made sense it would be easy to fix.
Occam's Razor
Why would it suddenly change? I removed the 20A fuse for the PCM and let it sit for like ten minutes to clear out the ecu, then drove it again. So far it seems a LITTLE better, but i need to give it time
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  #13  
Old 12-07-2014
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Could cleaning the clutch switch help?
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Old 12-07-2014
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Okay i started her up tonight. i know it's too early to tell but it seems unplugging the ECU fuse and letting the ecu reset done did the trick. idk why it was acting up but now it SEEMS she has corrected herself.
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Old 12-07-2014
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Good work
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Old 12-08-2014
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Alright so the issue seems to still be there, albeit in a much smaller, less annoying way. I'm definitely gonna try taking out the IACV tomorrow and watching its operation outside of the intake pipe.

More importantly though is a discovery i made. While sitting at a stop light in neutral for instance, it will stay around 1400 rpm, and EVENTUALLY go down to about 850 rpm, although the amount of time it takes to do this follows no noticeable pattern. I noticed if i pop it into gear (first, for example), and WITHOUT using the gas, just the clutch, slowly begin to load up the engine and move the truck (which brings down the revs), and then put it back into neutral, it stays down. For example, sitting at 1400 rpm, i put it into first and let the clutch out partially, which drops the revs to about 700, and then put the clutch back to the floor and put it in neutral, the rpms will then stay at 850 where they should be. Almost like the idle gets "stuck" at 1400 rpm and i have to "unstick" it by manually dropping the rpm. Is that an IACV issue? Would cleaning the IACV help this?
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Old 12-09-2014
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As RonD pointed out in an earlier post, could the cruise cable (if equipped) be sticking?

Throttle cable? New cars no longer have a throttle cable, and have gone to a "drive by wire" method to prevent the throttle cable from sticking, causing people to drive their vehicles into walls, houses, buildings, etc. Our older Rangers still have this throttle cable though.
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Old 12-09-2014
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Originally Posted by RonD View Post
You have an issue with IAC Valve or Vacuum leak if RPMs stay high when IAC is unplugged.

The point of the IAC Valve is computer controlled idle RPMs, this means with IAC closed all the way idle should be lower than lowest RPM wanted, 500 is usual but it can be lower and engine may stall.
If it is staying at 800 then there is a problem for sure, manual trans idle should be 650-700 in any case
Automatics use 750-800

If possible remove IAC from intake, leave wire connected, and turn on key, IAC should open all the way, now unplug wire, IAC should close all the way.
This is just to make sure it can close all the way, if not then that could be causing higher idle and delay in idle dropping.
Clean it and see if you can get it to close.
Also make sure vent on the back side is clean, that allows valve to open and close without having air trapped behind it.
The IAC valve's engine air passages are on either side of the throttle plate.

If it is closing then put it back on and leave wires disconnected, and remove vacuum line from intake manifold one at a time and block the port, when idle drops you found the leak
im gonna try this right now
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Old 12-09-2014
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Originally Posted by bucko View Post
As RonD pointed out in an earlier post, could the cruise cable (if equipped) be sticking?

Throttle cable? New cars no longer have a throttle cable, and have gone to a "drive by wire" method to prevent the throttle cable from sticking, causing people to drive their vehicles into walls, houses, buildings, etc. Our older Rangers still have this throttle cable though.
how would i verify that it is sticking?
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Old 12-09-2014
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i pulled it off, and watched inside the iac for any change between koeo and koeo, nothing. am i supposed to attempt to start the engine? is it supposed to be a cold engine?
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Old 12-09-2014
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Originally Posted by bucko View Post
As RonD pointed out in an earlier post, could the cruise cable (if equipped) be sticking?

Throttle cable? New cars no longer have a throttle cable, and have gone to a "drive by wire" method to prevent the throttle cable from sticking, causing people to drive their vehicles into walls, houses, buildings, etc. Our older Rangers still have this throttle cable though.
i dont believe the cruise is stuck. it has slack
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Old 12-09-2014
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No, don't start the engine with IAC removed, engine will race.

With key on IAC valve should open all the way, but it depends on the software, it may not open until Crank sensor Pulse starts.

Engine off, open throttle plate and remove both cables.
Start engine, open throttle and release, see if it sticks.
Repeat test adding back only 1 cable at a time.
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Old 12-09-2014
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Originally Posted by RonD View Post
No, don't start the engine with IAC removed, engine will race.

With key on IAC valve should open all the way, but it depends on the software, it may not open until Crank sensor Pulse starts.

Engine off, open throttle plate and remove both cables.
Start engine, open throttle and release, see if it sticks.
Repeat test adding back only 1 cable at a time.
I DID not start the engine. I removed the iacv from the throttle body and looked inside it while having the key turned to the ON position. I felt the IACV "twitch", but nothing inside it moved. I then removed the plug and nothing inside the IACV moved. THE ENGINE WAS WARM. Should I do this test with a cold engine?
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Old 12-10-2014
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Originally Posted by 420stackz View Post
i pulled it off, and watched inside the iac for any change between koeo and koeo, nothing. am i supposed to attempt to start the engine? is it supposed to be a cold engine?
bump
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Old 12-10-2014
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lets run through it one more time:

Removing IACV electrical plug from circuit gives desired effect. Eventually it will throw a code for IACV circuit.

Removing IACV electrical plug does not impact the idle in any way while the engine is running.

With IACV physically removed, nothing inside seems to move around no matter what i do with KOEO (both cold and hot engine).

Throttle plate is not sticking.

And once again, none of this happened until i removed the battery and started cleaning all the ground wires.
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