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Old 02-12-2020, 08:38 PM
flounder flounder is offline
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Default rough idle, won't stay running, runs fine with MAF disconnected

93 xlt 2.3l 130kmiles
First KOEO codes: 121= throttle position sensor out of self test range or
throttle position voltage inconsistent with MAF sensor. Double checked for any vacuum leaks and replaced TPS. No change. Test voltages to MAF sensor, check out o.k. but cannot run proper MAF test or KOER codes due to engine won't stay running. Replaced MAF sensor. No change. Engine runs fine with MAF unplugged due to stored baseline data. Cleared codes re test KOEO and
pull these codes: 157= MAF below minimum voltage
158= MAF above max voltage
543= Fuel pump circuit open, battery to PCM
The only thing between the battery and the PCM is the fuse (ok) the inertia switch (ok) and the fuel pump relay, so I replaced the relay. No change.
I would not suspect a an ignition or a fuel pump problem since it runs fine with
with MAF disconnected. My Haynes manual is pretty useless when it comes to individual component tests. My next guess would be testing the PCM or the electrical to the EGR ( diaphragm holds vacuum). Any help with test procedure info. or suggestions would be much appreciated. I usually won't replace a part unless I get a solid diagnostic on the problem , however this one is taking me on quite a ride and I need my truck back.
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93 Ranger xlt
2.3 / 4cyl.
2wd
125k miles
stick shift
all stock

Last edited by flounder; 02-12-2020 at 09:49 PM.
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  #2  
Old 02-13-2020, 06:09 AM
djfllmn djfllmn is offline
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Default Re: rough idle, won't stay running, runs fine with MAF disconnected

check the wiring from the MAF back to the PCM
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  #3  
Old 02-13-2020, 03:44 PM
flounder flounder is offline
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Default Re: rough idle, won't stay running, runs fine with MAF disconnected

all voltages and grounds are correct as is the resistance from maf to pcm on all 4 wires.
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93 Ranger xlt
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2wd
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stick shift
all stock
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Old 02-18-2020, 02:38 PM
tomw0 tomw0 is offline
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Default Re: rough idle, won't stay running, runs fine with MAF disconnected

Do you have VREF to MAF? It uses a fixed/specified voltage to run the heater wires that are monitored... if VREF is wrong, or questionable ground, the current used will be wrong, and reported as out of range, possibly.
tom
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Old 02-18-2020, 11:06 PM
flounder flounder is offline
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Default Re: rough idle, won't stay running, runs fine with MAF disconnected

Hey Tom, Thanks for the response. I'm not sure what VREF is. I found a procedure to all 4 wires from the PCM. 2 had 12volts and 2 had ground. Unable to test in running mode since it won't run with the MAF plugged in. Can you guide me to some info. on testing VREF? Thanks
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93 Ranger xlt
2.3 / 4cyl.
2wd
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stick shift
all stock
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