93 4.0 high idle/stalling


Tstiles216

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Hello, and thanks for taking the time to read this and showing your interest. I have a 1993 4.0 ranger that has been having some issues with a high idle and recently within the past couple weeks it will stall intermittently. Whenever I first start it, idle runs high around 2k +. After it runs for a minute it will idle down. Usually it runs fine after that but recently after driving for a bit the idle will spike back up around 2500 rpms if I am in neutral or have the clutch in. (Almost seems as if the hot days play a role in it as it seems to happen only when it’s hot out, temps have been pretty high the past few weeks). Then if I’m taking off from a stop or pulling around a Corner at slow speeds say like 2nd gear it just shuts off and dies. It will start back up after I wait at least 45 minutes to a hour or so. I am trying to explain this as best as possible sorry if it is confusing.

Now I will go over what I have done to try and figure this out. I put a gauge on my vacuum port of the intake and it is holding good vacuum. Koeo code of 121(TPS) and a KOER code of 172 (02 reading lean). I have gone over ground connections and those all seem to be ok. About 5 years ago the ecu went bad and unfortunately back Then before I had any knowledge of how anything worked I replaced pretty much every sensor on the truck along with the IAC and I can’t even remember all what else before I got a new Ecu and fixed the problem. I have not since checked said sensors as they weren’t bad to begin with back then and I highly doubt any of them has shit the bed in the past five years since they were unnecessarily replaced. I’m pretty stumped as to what the issue could be, could this be a intermittent fuel pump failure? Was thinking about going up to rent a pressure tester if they have one available for loan a tool service. Any input is appreciated thanks in advance guys.
 


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RonD

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Welcome to TRS :)

Good descriptions

Whats "good vacuum", need numbers, 18-21" is expected, and steady, no jumping around

After engine is warmed up, 5-8 min maybe, let it idle and unplug the IAC Valve's 2 wire connector, RPMs should drop to 500 or engine may even stall, either is GOOD, it means no vacuum leaks
If idle stays high you have a vacuum leak, simple test

Fuel filter, when was it changed last?
If filter is getting clogged up it will cause lower fuel pressure(lean code) and stalling, then a wait to restart
Fuel pump can cause same issue, but filter is cheap and easier to get at, lol

If you can get a hold of a fuel pressure gauge, you should see 30psi running pressure, raise RPMs to 2,000+ and hold it there, make sure pressure is not slowly dropping, should stay between 30-35psi


Check throttle plate, and its spring, spring needs to be good or 20" of vacuum WILL hold throttle plate open a bit
The TPS(throttle position sensor) is connected to throttle plate

Code 121 - Throttle Position (TP) sensor out of range
May mean the throttle plate is not closing all the way, so TPS doesn't show under 1volt
The throttle plate sticking could cause the higher RPMs AND 121 code, although Lean code, no probably not
With engine idling check if you can manually close throttle plate a bit more
If you have cruise control disconnect that cable from throttle linkage, for a day or so
Also disconnect gas pedal cable and check it for binding, lube it while its off, and check if engine idles lower while its off

TPS gets 5 volts from computer, several other sensors use the same 5volts, grey/red wire
Center wire on TPS sends back .69 to 4.6volts to denote throttle plate position
.69-.99v with throttle closed, under 1volt
4.5-4.7v with throttle plate Wide Open(WOT)
You can test center wire with volt meter using a sewing needle to pierce the wire
Key on engine off
test voltage and open throttle plate manually, should be steady voltage up and down, no jumping or dropping, if so replace TPS
 
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Tstiles216

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Thanks Ron, yes my vacuum was at 20. I will start with checking my cables and springs and you suggested and get a fuel pressure gauge and test that as well. I have a multimeter but I’ll have to get myself a little needle to pierce the wire. Also I’ll go ahead and slap on a new fuel filter and get back with you. Is it common for fuel pumps to get hot and fail then work once allowed time to cool off? I’ve never had a fuel pump go bad on anything so I am not familiar with those symptoms.
 

Tstiles216

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I forgot to mention I did perform the test of unplugging the IAC..... saw you tell somebody else to do that in a different post lol
 

RonD

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Yes electric motors can fail when they get hot, gasoline cools the pump off, so if issue(stalling) shows up more when fuel level is 1/4 or less it may be pump over heating

So what was the result of the IAC Valve test?
 

Tstiles216

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It passed the IAC valve test..... hopped in my 2013 Sierra 1500 to go up to oreillys and it must have a parking brake that’s stuck or a locked up caliper cause it won’t move. Hopefully I can get this figured out so I can get back to working on the ranger. I still have my dads 03 ram or girlfriends 03 caravan to get me up to the parts store..... I would rather not a Chrysler save the day but 🤷🏻‍♂️
 

RonD

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So RPMs drop to 500 or engine stalled?
 

Tstiles216

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the Rpms dropped to 500
 

RonD

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So either the computer is opening the IAC Valve too much, long shot

OR

Throttle plate is sticking, TPS code
Take TPS off, it can also cause throttle plate to stick, make sure its easy to turn
 


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