4.0L OHV & SOHC V6 Tech General discussion of 4.0L OHV and SOHC V6 Ford Ranger engines.

EXTREMELY High Idle

  #1  
Old 02-11-2019
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EXTREMELY High Idle

04 4.0 5 speed 145,000miles.

When I start the truck cold or warm, idle INSTANTLY is between 2000-3000

When driving the truck and I go to upshift or down shift from about 2000 or lower, the rpm jumps up to 2000-3000

When I come to a stop, the idle comes down to about 1000 for about 1-2 second and then just goes right back up to 2000-3000

Dare I say I could deal with the high idle. But It worries the hell out of me to start it with zero oil pressure and run it right up to 2000-3000 rpm
 
  #2  
Old 02-11-2019
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Originally Posted by Diesel_Brad View Post
04 4.0 5 speed 145,000miles.

When I start the truck cold or warm, idle INSTANTLY is between 2000-3000

When driving the truck and I go to upshift or down shift from about 2000 or lower, the rpm jumps up to 2000-3000

When I come to a stop, the idle comes down to about 1000 for about 1-2 second and then just goes right back up to 2000-3000

Dare I say I could deal with the high idle. But It worries the hell out of me to start it with zero oil pressure and run it right up to 2000-3000 rpm
check for any VAC leaks, check to make sure the IAC motor is working correctly and make sure the throttle body is returning to idle position
 
  #3  
Old 02-11-2019
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Originally Posted by djfllmn View Post
check for any VAC leaks, check to make sure the IAC motor is working correctly and make sure the throttle body is returning to idle position

No vacuums leaks. Verified by unplugging IAC.
IAC does open and close
Throttle body returns fully closed
 
  #4  
Old 02-11-2019
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Oh. When I unplug the MAF, the idle returns to normal
 
  #5  
Old 02-11-2019
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Air flow is what sets RPMs, not fuel flow

If you add fuel to a running gasoline engine you get a flooded engine, if you add more air you get higher RPMs

Computer(PCM) controls air flow via the throttle plate by-pass using the IAC Valve
Driver controls air flow via the gas pedal/throttle plate

Vacuum leaks cause higher RPMs because.......................wait for it....................YES, extra air flow via that air leak
Failing and stuck open PCV Valve causes what you describe

After engine is warmed up, and idling, unplug the IAC Valve's 2 wires, it should close
RPMs should drop down to 500 or so, or engine may stall, either is GOOD, no vacuum leaks
If RPMs don't drop then try pulling throttle closed more, maybe its not closing all the way, failing spring or cable issue or ??
Cruise control cable could be holding it open
It takes a GOOD spring to hold and close the throttle plate when engine is running, there is 18+ inches of vacuum in the intake, thats alot of suction, so weak throttle spring can cause what you describe
Engine off, open and close throttle plate, makes sure its not binding, and make sure it SNAPS closed if you release it at wide open
If throttle plate seems OK then you have a vacuum leak if RPMs don't drop

If idle does drops down to 500 then IAC Valve was being TOLD by the PCM to open up too far, so PCM issue, there may be a software update for it, call Ford dealer and give them the VIN number, they can check.

PCM issue would be the only reason unplugging the MAF might effect idle
PCM already knows its running a 4 liter engine, thats the software it has inside it, so it already know how much air will be coming in at any given RPM, just math
What the MAF is for to to tell the PCM the WEIGHT of the incoming air
Cold air is heavier than warmer air, i.e. "hot air rises", it rises because it lighter than colder air
Higher elevation air is lighter/thinner than air at sea level

gasoline air mix is 14.7:1 ratio, thats 14.7 POUNDS of air to 1 POUND of gasoline
Or 14.7 grams of air to 1 gram of gasoline
So its a WEIGHT ratio, not volume, PCM needs to know the weight of the air and also the air temp, so there are two sensors, MAF and IAT(intake air temp), neither should effect RPMs they will effect Lean or Rich running, but not RPMs/air flow


In the mid 1990's manual Rangers got a software that holds RPMs high when shifting gears, and RPMs should stay at 1,000 or so UNTIL speedometer shows under 5MPH, then it should drop down to say 700 or so
These are for emissions requirements
If you are at say 2,500 RPMs and push clutch pedal in the RPMs should stay the SAME, not go up , unless engine was under BIG LOAD, lol
And RPMs should stay at 2,500 for 5 seconds or so, allowing you to shift, after 5 seconds if clutch pedal stays in, they should drop down to 1,000 and stay there until speed is under 5MPH
 
  #6  
Old 02-11-2019
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Originally Posted by RonD View Post
Air flow is what sets RPMs, not fuel flow

If you add fuel to a running gasoline engine you get a flooded engine, if you add more air you get higher RPMs

Computer(PCM) controls air flow via the throttle plate by-pass using the IAC Valve
Driver controls air flow via the gas pedal/throttle plate

Vacuum leaks cause higher RPMs because.......................wait for it....................YES, extra air flow via that air leak
Failing and stuck open PCV Valve causes what you describe

After engine is warmed up, and idling, unplug the IAC Valve's 2 wires, it should close
RPMs should drop down to 500 or so, or engine may stall, either is GOOD, no vacuum leaks

Truck stalled

If RPMs don't drop then try pulling throttle closed more, maybe its not closing all the way, failing spring or cable issue or ??
Cruise control cable could be holding it open
It takes a GOOD spring to hold and close the throttle plate when engine is running, there is 18+ inches of vacuum in the intake, thats alot of suction, so weak throttle spring can cause what you describe
Engine off, open and close throttle plate, makes sure its not binding, and make sure it SNAPS closed if you release it at wide open
If throttle plate seems OK then you have a vacuum leak if RPMs don't drop

Throttle plate snaps closed

If idle does drops down to 500 then IAC Valve was being TOLD by the PCM to open up too far, so PCM issue, there may be a software update for it, call Ford dealer and give them the VIN number, they can check.

PCM issue would be the only reason unplugging the MAF might effect idle
PCM already knows its running a 4 liter engine, thats the software it has inside it, so it already know how much air will be coming in at any given RPM, just math
What the MAF is for to to tell the PCM the WEIGHT of the incoming air
Cold air is heavier than warmer air, i.e. "hot air rises", it rises because it lighter than colder air
Higher elevation air is lighter/thinner than air at sea level

gasoline air mix is 14.7:1 ratio, thats 14.7 POUNDS of air to 1 POUND of gasoline
Or 14.7 grams of air to 1 gram of gasoline
So its a WEIGHT ratio, not volume, PCM needs to know the weight of the air and also the air temp, so there are two sensors, MAF and IAT(intake air temp), neither should effect RPMs they will effect Lean or Rich running, but not RPMs/air flow


In the mid 1990's manual Rangers got a software that holds RPMs high when shifting gears, and RPMs should stay at 1,000 or so UNTIL speedometer shows under 5MPH, then it should drop down to say 700 or so
These are for emissions requirements
If you are at say 2,500 RPMs and push clutch pedal in the RPMs should stay the SAME, not go up , unless engine was under BIG LOAD, lol
And RPMs should stay at 2,500 for 5 seconds or so, allowing you to shift, after 5 seconds if clutch pedal stays in, they should drop down to 1,000 and stay there until speed is under 5MPH
If I am cruising at 2000rpm and I upshift the RPMs can hang at 2 or sometimes go up to 3000. It depends

I come to a stop. The RPMs come down to 1000 or so then climb right back to the 2000-3000rpm


Oh, NEW Motorcraft IAC, TPS and MAF all within last 500 miles

So I guess you are saying PCM issue
 
  #7  
Old 02-11-2019
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Yes, PCM is doing it using the IAC valve, and it doesn't "think" anything is wrong or it would set a code

Found this TSB in another thread here:
4.0L M/T - HIGH IDLE BETWEEN SHIFTS OR IN NEUTRAL
TECHNICAL SERVICE BULLETIN
Reference Number(s): TSB 05510, Date of Issue: March 21, 2005
FORD:2004-2005 Ranger

Related Ref Number(s): TSB 05510
ARTICLE BEGINNING
DESCRIPTION
HIGH IDLE BETWEEN SHIFTS OR IN NEUTRAL - 4.0L ENGINE WITH MANUAL TRANSMISSION
ISSUE
Some 2004-2005 Rangers equipped with a 4.0L engine and manual transmission, may exhibit a higher than expected idle between shifts, during a coast down with the clutch depressed, or with the transmission in neutral.
ACTION
Reprogram the powertrain control module (PCM) to the latest calibration level using WDS release B35.9 and higher, or B36.2 and higher. Calibration files may also be obtained at www.motorcraft.com.
NOTE:THIS NEW CALIBRATION IS NOT INCLUDED IN THE B36.0 CD.

WARRANTY INFORMATION
WARRANTY STATUS: Eligible Under Provisions Of New Vehicle Limited Warranty Coverage.
Sbcjeep posted it back in 2011





Reads like a software update may be needed, Ford does charge for this, out of warranty
Call first with VIN number and see what they charge the service, and IF they have the software on hand, i.e. NOTE:THIS NEW CALIBRATION IS NOT INCLUDED IN THE B36.0 CD.
 

Last edited by RonD; 02-11-2019 at 09:31 PM.
  #8  
Old 02-12-2019
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The weird thing is I have put almost 5000 miles on the truck in the past month with no issues(put the truck on the road in the end of december). This just started late last week
 
  #9  
Old 02-12-2019
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Yes, that would be the way a software issue(glitch) would happen

If it happened when vehicle was new they would have changed it then
 
  #10  
Old 02-12-2019
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Well, I swapped the ECM with my other 04. Idle back to where it should be
 
  #11  
Old 02-12-2019
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Good work, found the problem
 
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