2003 Gt Engine Failure

Discussion in 'SN95 4.6L Mustang Tech' started by Jinx, Jun 22, 2013.

  1. The scanner only reads the ODBII codes. It is an older Diablo handheld tuner that I bought shortly after buying the car. I will look into that web site and see what they have to offer. Was that price you gave for the hose, boot and valve the one for the standard valve or the heated valve? My GT has the heated valve.
  2. Not sure to be honest, I didn't know there were 2 different ones.

  3. yeah, not sure why they have to heat the PCV valve, but it does cost about 10x's as much as a "normal" valve. :notnice:

    and it's probably tied into the ECM somehow so you can't just unplug it and use a normal valve.
  4. Guess I was lucky on the Mach 1, the valve I got looked exactly like the one I had and was cheap. You can order by motorcraft part number from Rockauto to make sure you get the right part.
    Jinx likes this.
  5. Results are in:
    1.) collapsing tubing assembly between PCV and TB. Replaced
    2.) IAC partially stuck open/closed due to carbon buildup. Option to clean or replace. Replaced
    3.) TB stop screw reset/recalibrated (per manufactures instructions) - no charge

    Thanks for everyone's input. It was very informative and helpful.

    oh and LaserSVT
  6. #2 is the part i just fixed twenty minutes ago on my wifes 03 explorer 4.6. took the service center 2 days and 3 different orders to get the correct part. third time they actually used the part number i had provided in the first place a lo and behold there she was. for future reference to those having this issue here is a link to show the part number. they are the same on the mustang and explorer.
    Modular2v likes this.
  7. PLEASE!!

    Not sure WTF is going on now.

    New IAC valve and gasket.
    Reset Throttle scew per instructions posted here. (shown below)

    I put the parking break on.
    I push the clutch in.
    I start the car in neutral, and then release clutch.
    Sitting parked the idle pops to 1500, hangs and then drops to about 750. Turn on the AC and idle climbs to just under 1000.

    all seems normal.


    I start driving around town and on the highway (this is where the issue comes in). At any cruising speed RPM level is where it is to be expected. However, when I press the clutch in at cruising speed the RPMs climb and hold at 1000 RPM above where they were and when I let the clutch back out they return to where they should be. While approaching a traffic stop, I start downshifting from 4th to first. As long as the cars is in gear the rpms seems normal. I reach the intersection and come to a complete stop with the car in neutral and the clutch depressed. At this point car is idling at 2300 RPM and does not want to seem to come back down. I turned the AC on at one point to put a load on the engine and that seemed to work, but not all the time. This happened again at the follow intersection and since there was no traffic around, I shut the car off, then restarted and the engine surged to 1500 then dropped gradually to about 750. I swear at one point later on when I was driving, the car was in 2rd gear and I let my foot off the accelerator and the RPMs seemed to never drop and the car continued on like it was on cruise control.

    Instructions I used**
    Resetting the base idle:

    Clear the computer's idle memory by disconnecting the battery for 20+

    -Disconnect the Idle Air Bypass solenoid
    -Reconnect battery
    -Start engine and set idle speed to desired RPM with idle screw on throttle
    -Turn off engine and reconnect the air bypass solenoid

    -Start engine and let it idle for 2 minutes with no accessories on.
    -Turn off engine for two minutes
    -Start engine again and run for 2 minutes with every accessory turned on.
    -Turn engine off again.
  8. See if you can pull the TIDs. I know I said it before but I had a similar issue with my Mach 1 and it turned out to be a faulty coil pack. I wasn't getting a missfire CEL but my coil pack was totally shot. I figured it out way before I got a CEL by reading the TIDs. Might be worth paying a dealer the minimum fee to read them and give you the info on it.

    It sounds like you have a bad injector, bad coil pack or possibly a vac leak. If it is a vac leak a smoke test will find it.

  9. can a Diablo Predator tuner pull the TID's??
  10. Ya go me, might want to call their tech support line to find out. I use Binary Editor with a Mongoose cable.
  11. as i posted a ways back in your thread, my wifes 03 explorer has the 4.6. changed everything you did except for one part you have not done yet. the TPS. everything else "helped" but the idle speed and the rpm drops while braking and eventually stalling led me to swap out a new TPS. had the vehicle scanned at my mechanics with a good code reader and it had nothing. swapped out and it runs like a top!
    Jinx likes this.
  12. I got to thinking... The mechanic said that they could not get the lower end of the TPS sensor within factory spec. So if the car is trying to rev down, but can't, do you think it could be because of the TPS sensor can't get the throttle plate to close all the way? So I thought, $70 for another diagnostics and $30 for labor, or just get a new Motorcraft TPS for $56. Well, picking up the new motorcraft part at O'reillys later today.
  13. I bought the bwd tps at advance online with a coupon code. 30 bucks and good to go
  14. FWIIW, the TPS is not used the same way after 1996+. The closed throttle TPS value is relearned at every engine start up. So the actual value of the TPS is no longer important. What is important is for the TPS to have the same value each time the throttle is closed.

    The TPS is a sensor. It does not close or change the throttle setting. The throttle return springs are responsible to actually close the throttle.

    If the motor is not able to rev down, that tells me there is too much air entering at idle. This is most likely from:
    1. The idle set screw is set too high.
    2. There is a vacuum leak after the throttle body butterfly valve.
    3. the IAC is not working
    4. the throttle linkage is binding or not closing fully.
    5. The TPS value is not stable. IE increasing after initial engine start up.
    6. The PCM does not have the car's correct speed. The PCM needs to know the car's speed to determine when to activate low speed vs high speed idle.
    Remember that the IAC is a bypass device. It can only ADD air (never remove air). So if the IAC duty cycle is 0% and the idle is still too fast, then no idle adjustment is possible.

    A basic functionality test of the IAC is to disconnect the IAC electrical connector. The motor should die outright or at the very least, the RPM's should drop to a very low level.

    More information on how to trouble shoot idle/IAC issues.

    Jinx likes this.
  15. :nice:
  16. So tired of this. put new TPS on and no change. In the process now of resetting the computer and going to try again in 30 minutes. At this point it ends up looking like I will have no choice but to take it to the dealer at some point, but not the local one. I will take the time and go the extra 20 miles to the other service center.

    At cruising speed and 5th gear, I can depress the clutch at 50mph and the RPM will climb from 1700 to 2300. Coming to a stop from 50 mph, by putting in neutral and braking, results in 2300 RPM at full stop. I can sometimes drop the RPM by flipping the AC on then off.

    While doing the same procedure at the next stop, instead of turning the AC on and off, I can just shut the car off then on and it will idle normally.
  17. It sounds like the fuel mixture is way off and the ECU is changing what the injectors are doing, causing the RPMs to climb to keep the engine alive. Could be a bad injector, coil pack or even the o2 sensors.
  18. Back from driving after a reset. After driving for a bit, every stop I came to, I would push the clutch in and the RPMs would climb to 2500 and hold until the vehicle came to a complete stop for 3 seconds, then they would sit at 750 perfectly fine.
  19. The force is weak on this one. 750 with the IAC disconnected is too high. No idle at all.

    Again, the way the idle works is with bypass air. Air that's in addition to the air already passing through the butterfly. At 750 the IAC duty cycle is already zero so no adjustment is possible.

    The motor should idle so low as to be a problem or die outright when the IAC is disconnected. Then and only then can the IAC add air to the idle and actually control the idle.

    I suspect that the instructions followed to set the idle are for a 95 and older model year.
    LaserSVT likes this.
  20. ^^^ on this advice, I will try to reset again tomorrow. What else have I got to lose. 450 to 500 should be about close to the cut out zone.