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2002 4.6L high idle...please help

Discussion in 'Stock 2002 - 2005 Explorers' started by r6bikerdave, October 9, 2015.

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    1. r6bikerdave

      r6bikerdave New Member

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      My 2002 explorer 4.6 is having issues with a high idle. It is a smooth idle around 2000 rpms(in park/neutral) even when engine is warm. No CEL is present. Last night I pulled the engine cover off and used a whole can of starting fluid to check for a vacuum leak but couldn't find anything. I have access to a genisys scan tool so I can pull a data-stream but not sure what I should be looking for. Doubt it is related, but last fall I had to replace the intake manifold(dorman) it had developed both a coolant and vacuum leak. I had also replaced the IAC valve(motorcraft) just prior to finding the intake issue. And also replaced the rubber inlet hose to the IAC valve(was leaking).

      Explorer was driving great for a whole year after all that work and now the high idle is back. It has about 193k, runs like a champ other than this idle issue!

      Thanks for your help/advice, DAVE
       
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    3. dla

      dla Active Member

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      I think your leak to the IAC is back. But, it is also possible that the temperature switch is bad, and the ECU thinks the engine is cold.
       
    4. lincolnshibuya

      lincolnshibuya Active Member

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      clean the throttle body, i believe too much crud in there that's causing the valve to not close completely. Also check if your throttle cable is in place correctly, it might be pulling a tension while at park/idle due to being dislocated or out of place.
       
    5. silverfox103

      silverfox103 Active Member

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      I am also watching this posting with interest. I have a 2003 Aviator, runs great. When you start it, it goes up to 1800 2000 rpm's, then drops down immediately to 750 ish rpm's, no other problems.

      Tom
       
    6. r6bikerdave

      r6bikerdave New Member

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      Throttle cable is not sticking/binding at all. Throttle body looks to be closing just fine. I tried disconnecting the wiring plug to the IAC valve(with the engine warm), and the idle returns to normal. I unbolted the IAC valve and can easily blow air through with my mouth...should I be able to?? Oh I did hook up a vacuum gauge, everything looks good there so I do not suspect a vacuum leak.

      Im still going to hook up a Genisys scan tool and look at the data-stream, anything in particular I should be looking for?

      Thanks for the help, DAVE
       
    7. Joe in NY

      Joe in NY Active Member

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      That is normal operation. Nothing wrong.
       
    8. r6bikerdave

      r6bikerdave New Member

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      Got my idle fixed! Last night I used the Genisys to pull a data-stream with the engine warm. Everything looked good except the TPS voltage was showing 0.86v and PT or "part-throttle" position without my pushing on the pedal. Closed throttle baseline was set @ 0.68v. First I unbolted the TPS sensor but left the electrical plug attached. The reading dropped to 0.54v and the idle dropped to normal. Now this through a DTC code because the voltage had dropped below the baseline, but the throttle position now showed "closed". Then with the engine off I removed the throttle cable, cruise control cable, and throttle body. Now signs of anything sticking and the throttle body had no build-up. I reinstalled the throttle body and TPS sensor, twisted the sensor slightly when attaching and was able to get the voltage down to 0.80. After attaching each throttle cable to TPS voltage had not changed. I even tried adjust the set-screw that the throttle body closes against, but the throttle was fully closed. Next I disconnected the battery for a few minutes. After connecting the battery and started the engine, idle was down below 1,000 rpms in park. Looked at the data-stream again, and the TPS base voltage was now set @ 0.80 and sensor was reading 0.81 and showing throttle position "closed"! Drove it around about 5 miles and everything is great!
       
    9. apenland01

      apenland01 Active Member

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      This is normal, it is to push the oil pressure quickly. It should flare on startup and then settle back.
       
    10. Joe in NY

      Joe in NY Active Member

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      The reason for the flare up on start up is because the Intake Manifold is not under vacuum. It has 14 psi (absolute pressure) in it. When you first crank the engine it has all of that air to consume. Then once it has consumed the air the intake manifold now goes into vacuum (gauge pressure) and the engine air is restricted by the IAC or TB.
       
    11. apenland01

      apenland01 Active Member

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      Huh, I thought it was to get the oil pressure up quick since the timing tensioners are hydraulic and pressured by the oil. At least that's what I read somewhere before. Haven't heard the intake manifold thing, but it makes a bit of sense.
       
    12. r6bikerdave

      r6bikerdave New Member

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      So my high idle has returned. Used a scan tool to look at that data stream and same issue as before. At idle, TPS sensor is reading 0.81v and "part throttle", but computer is showing closed throttle to be at 0.60 volts.....why does the baseline voltage keep dropping? Computer issue? TPS sensor bad? Thanks
       
    13. 2000StreetRod

      2000StreetRod Staff Member Moderator Elite Explorer

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      ratchet function

      According to the 2002 OBD-II System Operation Summary the PCM checks for out of range sensor voltage:
      "Typical analog sensor check malfunction thresholds:
      Voltage < 0.20 volts or voltage > 4.80 volts"

      On 2nd generation and later PCMs there is a ratchet function that measures the TPS voltage at ignition turn on and assumes that to be the closed throttle voltage. The PCM periodically checks for a lower value and if found sets that as the closed throttle value.

      If your idle is fast then excess air is entering the intake system. Possible sources are: open throttle plate; IAC valve; intake manifold leak(s); or vacuum hose(s). Since you have access to a scanner I suggest that you read the commanded idle speed and the actual engine speed. If the commanded speed is significantly less than the actual speed then the PCM is unable to control the engine idle speed. Investigate the items listed in the 2nd sentence of this paragraph. Using aerosol starting fluid is an unreliable method to detect vacuum leaks because the PCM rapidly changes the IAC valve in an attempt to maintain a constant idle speed. The only reliable method to locate a vacuum leak is with a smoke machine.

      If the commanded and actual engine speeds are approximately equal but higher than normal then you need to determine why. Read the engine coolant temperature (ECT) pid to see if it reflects actual conditions.

      Edit: I looked thru your past posts and found you were thinking about buying a replacement intake manifold about a year ago. Did you purchase the Dorman unit and if so is the cap still closing the unused port on the passenger side?
       
      Last edited: November 26, 2015
    14. Autolabs

      Autolabs New Member

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      Before you start chasing the fluctuating tps check this 1st. With that handy genesis scanner select output controls and select the test for the iac. If it's like a snap on verus it should give you the option of selecting the iac duty cycle be 10 percent increments. Go through each one and note the rpm change for each step. If there is a big jump in rpm with one of the 10 percent increments than it is probably a failed Iac. As you are probably aware, replace with motorcraft only. If this is not the case then monitor your fuel trims. If you indeed have a vacuum leak the fuel trims will be high at idle and become normal under acceleration. I chased a fluctuating c/t tps value last month on a ranger to find out it was an aftermarket iac valve. Good luck
       
    15. r6bikerdave

      r6bikerdave New Member

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      Disconnected battery last night to reset closed throttle voltage. Went to the forrest to cut a christmas tree today and idle was high when we got home. Pulled data stream again and everything looks good(except closed throttle again at 0.60v). Coolant temp is correct. Did the incremental test on the IAC, responded in equal amounts with each 10% added on the test. Fuel trim at idle is -2.3/-2.7 long term(bank 1/2) and short term was about -0.50 for both banks. With throttle added, both short/long terms went to 0 (if I remember correctly). I have no idea what the fuel trim should be. I used the scan tool to reset the computer by reseting the "KAM" (keep alive memory I assume?). Idle immediately fixed and closed throttle voltage @ 0.80v. When idling correctly the "desired engine speed was 672 or 762 I don't remember. Actually rpm was only 8-10 rpm's higher. Didn't mention it in the original post, but I had replaced the IAC and TPS before replacing the intake. I did NOT use motorcraft parts. Then found the coolant leak from the intake so I replaced that(Dorman). Idle was funky but only sometimes, then was reading about IAC being picky with Ford only parts so I replaced with Motorcraft. I have not replaced the TPS since the original time. Dont remember the brand, got it from rock-auto. I'm going to get a Motorcraft TPS sensor and see what it does. And on the Dormant intake manifold, yes the plug is still there on the passenger side rear.....isn't that a coolant line though? Thought I had read somebody had theirs blow off and loose coolant.
       
    16. 2000StreetRod

      2000StreetRod Staff Member Moderator Elite Explorer

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      read tps

      I suggest that you turn the ignition on but don't start the engine. Set your scanner to display the relative throttle position (Throttle position relative closed throttle) and then slowly depress the accelerator. The readings should smoothly increase from 0 at idle to 750 (or 0% to 100%).

      I also suggest that you monitor ECT with the scanner.
       
      Last edited: November 30, 2015
    17. Autolabs

      Autolabs New Member

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      I agree with streetrod. Monitor tps and cts. Does the idle ever come down after cold start and then goes high after driving? Check your 5 volt ref to the tps. Ideally check it when your closed tps voltage decides to drop. Possibly something else bringing down the 5v a little bit intermittently? Just throwing some possibilities out there for you that dont require more $ to find out. Also try disconnecting alternator incase extra ac ripple is causing some havoc.
       
    18. SyberTiger

      SyberTiger Active Member

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      Wow, this is eerily familiar. I'd been dealing with fast idle problems on and off for 5 years. I replaced the IAC with a Motorcraft and it seemed to go away, then on and off every 3 to 6 months since then I'd get the fast idle problem again. Typically, I would clean the IAC and the throttle body and the problem would go away for a few months. Now, having looked back, I believe what was "fixing" my problem was the fact that I always disconnected the battery when cleaning the IAC.

      Fast forward to about 14 months ago I replaced the intake manifold with a Dorman aftermarket because I noted a slight coolant leak. After the manifold replacement I noted my fast idle problem went away and concluded there was also a slight vacuum leak into the head(s)...meaning the problem was likely a slight vacuum leak around the intake manifold. Well, low and behold, a few days ago I'm having fast idle problems again.

      You can see HERE where I started a new thread to figure out was a scanner can tell me. Curious to know how you eventually diagnosed and fixed the problem you originally posted in this thread?
       

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