Truck starts Idles for 3-4 min then dies

Tiny
F150MAN2
  • MEMBER
  • 1994 FORD F-150
  • 5.0L
  • V8
  • 4WD
  • MANUAL
  • 130,000 MILES
When starting the truck cold it will run at a slightly high idle approx 1300-1400 rpm then will go down to 1000 rpm after a few seconds. Without touching the throttle it will run smoothly for approximately 3-4 minutes then die. It will restart but not stay running unless I feather the throttle. It will not rev over 2500 rpm's no matter how I feather the throttle. I have completed a full tune up (plugs, cap, rotor, fuel filter, and wires) verified (twice) firing order 13726548. Fuel pressure test KOEO of 35psi and running 40psi, fuel pressure does not cut out when engine dies. Verified timing at 10 deg. TPS was tested (prior issue was that it would run for the 3-4 min then when the throttle was pressed the engine would die and not restart until engine was cold), TPS failed test and replaced. Still same results. IAC tested (failed by ohm test) replaced, same results. Checked for vacuum leaks by spraying ye old carb cleaner no change in RPM"s. Tried spraying carb cleaner down throttle body to see if RPM's would go higher, no change. Only DTC is 126, according to my source is that MAP sensor is higher or lower than expected. The only showing I have to test the MAP sensor is with a mulitmeter with hertz, the one item on my multimeter I do not have. I really detest "throwing parts" at a vehicle and want to make sure if there is another way to test the MAP. Or is there possibly something else a problem? Thank you so very much for what you guys do!
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Sunday, February 2nd, 2014 AT 7:41 PM

5 Replies

Tiny
HMAC300
  • EXPERT
Check to see if the vacuum line going to map sensor is soft or cracked. If it is replace it then see what happens.
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Monday, February 3rd, 2014 AT 8:14 AM
Tiny
F150MAN2
  • MEMBER
Checked vacuum line visually, physiclally, and with liberal amounts of carb cleaner. Unfortunately no soft spots, cracks or leaks.
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Monday, February 3rd, 2014 AT 10:16 AM
Tiny
HMAC300
  • EXPERT
Then it's either the sensor or the wiring going to it or a pcm problem or compression or things like a timing chain. Also make sure the egr isn't flowing to much as this can effect it as well. Do this test to see if it is the map sensor.
Attempt To Eliminate Code 22/126 Plug MAP sensor vacuum supply hose. Start engine, and run it at 1400-1600 RPM. Slowly apply 15 in. Hg to MAP sensor. Perform KOER SELF-TEST. Check for Code 22/126, disregarding any other codes at this time. If Code 22/126 is still present, replace MAP sensor. If Code 22/126 is not present, inspect MAP sensor vacuum supply hose. If hose is okay, service other codes at this time. If no other code is present, check engine mechanical condition for cause of low vacuum also for the heck of it you could replace the hose leading to map sensor.
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Monday, February 3rd, 2014 AT 12:38 PM
Tiny
F150MAN2
  • MEMBER
I plugged the vacuum line, put 15in Hg. To sensor, and it ran without dying. Idle was around 900 RPM and would rev as normal. I did as you said and placed a different line to the MAP while the other was still plugged off. So tracked down to what I think was the issue, a vacuum tee/check valve. I assume it is a check valve that is, kind of black and white with what appears to be a valve or filter? It had one line going to the MAP and one going to what appeared to be the heater controls. After removing the valve and placing stock line to the MAP it ran without any stalling. Took it for a test drive and it did ok, once the rpm's would not drop back to idle when letting off the throttle. When I got back home it would idle like it had a massive cam in it. The KOER test the DTC 126 did not come back, only got 129, 173, and 334. Thank you for the help. I have been pulling out what hair I had left to get this issue taken care of, having someone with a fresh perspective has helped tremendously.
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Monday, February 3rd, 2014 AT 7:40 PM
Tiny
HMAC300
  • EXPERT
Enclosed is a vacuum diagram so if anything elseis amiss you can fix it.
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Tuesday, February 4th, 2014 AT 5:50 AM

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