94 2.3l rough idle when warm, worse after new radiator. Possibly mass air flow sensor?


STPL

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Hi all! Looking for some opinions on where to start here. This truck has always had a coolant temp issue, it barely registers 1/8 of the way up the gauge when hot. I read a few threads about the engine running on the colder side of the gauge so I didn't consider it an issue. Slowly, it seems the idle is starting to get worse and worse. I cleaned the IAC Valve and the truck starts up with more pep, but as it warms up the idle gets rough and the engine starts to vibrate. It never feels like its going to die, but something is clearly off. Recently its been feeling like its down on power as well.

When the engine is idling poorly, if I give it a little bit gas it smooths out and stops vibrating.

I cleaned the IAC which improved the cold idle, and if I unplug the IAC when running the idle gets worse. Plug it in and it gets better. Im going to take that as a sign the IAC is functioning normally. Sounds good?

If I unplug the MAF (Mass Air Flow Sensor) while the engine is running I get no change. Still the same rough idle. Does that mean the MAF is shot? I would assume that the idle would differ if I unplugged it.

I replaced the thermostat about a year ago just for basic maintenance before I got the truck on the road so I don't have any knowledge of how it ran with the old thermostat. I was running the old radiator with just water in the system for the better part of a year and finally got around to replacing the old rad and filing the system up with coolant. I had heat in the cab when i was running water, but now there is barely any with the new radiator and thermostat. Now the temp gauge barely gets off the bottom of the gauge and right above the bottom line above the "C". I notice there are a few different thermostats available for this ranger. Some are 160*, 180* and 195*. If I put a 15 degree lower thermostat in the truck will it throw off the temperature by gauge that much?

Fuel filter is less than two years old. I'm not ruling out the fuel rails being bad, is there a test for that?

Im thinking this could be a MAF issue or a coolant sensor issue thats throwing off the computers air/fuel mixture. Im not completely ruling out a misfire, but the coil packs all produce a spark when I remove the wire from the coil pack. It could still need a new IAC as well, cleaning it out might not have completely saved that one.

Of course I appreciate any and all advice! Let me know your thoughts and if you have any questions.
 
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STPL

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Heres the newest update. I ran all of the CELs and this is what I came up with. I was just unplugging the MAF, temp sensors, 02 sensors while the truck was running looking for a change in idle. I am now realizing that the KOEO codes could be from that, I will try to reset those codes and see what happens. I drove 10 or so miles with the MAF unplugged this morning and nothing seemed to change. Still down on power and idling poorly. Any input about any of this is welcome!

Key On Engine Running: Code 538 flashed twice. In the Haynes manual 538 checks out to be
538 - Invalid cylinder balance test due to CID circuit failure
538 - Invalid Cylinder balance test due to throttle movement during test
538 - Insufficient change in RPM/Operator error in Dynamic Response Check

I did not touch the throttle during this test.

Key On Engine Off: 8157158172218222118157
I can grab a few codes out of this string of numbers

157: MAF Below Minimum Voltage
158: MAF Above Maximum Voltage
172: Lean Bank #1
182: Adaptive fuel limit lean at idle
211: Profile ignition pickup circuit failure
118: Coolant temp sensor above max voltage/indicates -40*F
181: Adaptive fuel limit reached at part throttle #1
 

RonD

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With the dual spark plug setup you can test spark plugs easily

With engine idling unplug either coil pack, 2.3l can run on just the 4 spark plugs, two per cylinder gives better performance

If engine stalls instantly then only that one coil pack is working
Plug it back in and restart engine
Unplug the other coil pack to test

If it stays running with either coil pack unplugged but there is a steady misfire with one then one of those spark plugs is not working
Check firing order first, easy to mix those up

The ICM(ignition control module) on the front of lower intake was a known issue with 1989-1994 2.3l Rangers
Its the source of CID signal failure and code 211 Profile ignition pickup(PIP) failure
These can be tested at most auto parts stores

The 538 codes are test codes so ignore them for now

code 118 is the big one, ECT sensor wires are shorted or ECT sensor is
This is a TWO WIRE temp sensor, not the ONE WIRE sender for the dash temp gauge
 

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You're the man, Ron! Thanks for the advice.

I tested the coil packs yesterday and the engine will idle poorly with either of the two coil packs unplugged, but stay running. I didn't specifically take note of a misfire, I'll retest and double check that. How will i know theres a misfire for sure? I will also pull and inspect the spark plugs, firing order and wires.

I suspect something might be up with the ECT, I sprayed the plug out with some cleaner yesterday. I don't know if that caused the code, or the code was there but spraying it caused a change in idle. Im going to reset the codes to clear the memory and go for a drive then recheck and see what codes are still active.

I will look into getting the ICM tested, I think I had the same CID code when my crankshaft sensor went bad.

I will report back with what I find.
 

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I think the no change with MAF unplugged thing should point you in the right direction... either that sensor is faulty or the wiring to it is shorted. In my experience, a dead MAF sensor can result in a truck that may not start or run at all or may idle and/or run at full throttle but will have big dead spots in between and backfire through both ends. I have seen this several times on 4.0 trucks.

If you can find a cheap MAF sensor at a junkyard, you could try swapping it out and see if there is a change before buying a new one.

You should also check for leaks in the intake duct between the MAF and throttle body... I have seen a bunch of them cracked and pulling air from outside and not through the MAF causes weird issues too.
 

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To test MAF by unplugging it the engine MUST BE warmed up, and then drive it

Computer "knows" its running a 2.3 LITER engine, so it knows EXACTLY how much air is coming in at any RPM and throttle position, its just MATH and thats all the computer is there for, to do the MATH.

MAF tells computer the WEIGHT of the incoming air, which is important since the 14.7:1 air:gasoline ratio is a WEIGHT RATIO
14.7 pounds of air to 1 pound of gasoline
14.7 grams of air to 1 gram of gasoline

MAF and O2 sensors are used for best power and MPG but are not needed for engine to run, computer doesn't use them until its warmed up in any case

157: MAF Below Minimum Voltage
158: MAF Above Maximum Voltage
Are from unplugging it

So yes clear the codes and run engine a bit
 

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Allright. This morning I unplugged the MAF and drove to work, about 30 minutes away, Mostly highway but some backroads too. Truck didn’t seem to drive any different. Still idled poorly and feels like I’m losing what little power this engine has.

After work I cleared the codes by jumping the self test pins on the OBD port, waiting for the computer to start reading the codes and then pulling the jumper wire out. I plugged the MAF back in and drove home. Possibly a slight increase in performance, but really hard to tell. Still idling poorly. Got home, let the truck sit for an hour and pulled the codes from the computer.

No codes at all. All 1s. Usually repeats 111 twice and then shows no more lights. That’s with engine on and off. I also started the test by turning the wheel, pressing the brakes, pressing the clutch and giving it a short burst of wide open throttle. That got rid of the 538 code like Ron suggested.

I believe those codes before we’re still in the memory from when I was unplugging different sensors trying to get a change in idle. I unplugged the MAF, ECT, and 02 sensors.

Now I’m back to square run with a poorly idling engine and no codes to go off of. I will continue to check through out the weekend and see if CELs come up.

I’m almost leaning towards a fuel issue. Injectors, fuel pump or fuel filter. I’m going to pick up a fuel pressure tester gauge set tomorrow and see what it reads.

I unplugged both spark plug wires from their respective spots on the coil pack and every time the second plug was unplugged the engine idled lower. I will fully inspect the wires and plugs tomorrow.

I also sprayed a whole can of carb/choke cleaner on every vacuum hose and gasket as well as half a can of break cleaner. Soaking it in some paces trying to get a change in idle. I’m not complete ruling out a vacuum leak right now, but it seems improbable.
 

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You should spray soapy water around for vacuum leaks, safer and cheaper, engine will stumble if it sucks any in

It doesn't run any better Cold?

Should have a higher idle when cold and then after a few minutes idle will be lower
This is a function of ECT sensor, computer and IAC Valve working together in Choke Mode
 

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Sorry for the long posts! I'm trying my best to be as detailed as possible. Im scratching my head at this one, but spirits are still high!

The truck runs fine when cold, then within a few minutes the idle comes down and it starts rumbling and idling poorly. It will run/drive, just not that well. I had it running for a good 20 minutes today explaining to a friend whats happening and the engine stumbled a few times while we were looking at it. It caught itself and came back to idling poorly. Heres what I tested today, I plan on running a fuel rail test and testing sensors with a multimeter tomorrow.

Checked for more KOEO CELs and came up with 121118222218222. Those might be from me messing with the truck the day before, so take them for what you will. I will clear the codes and drive it tomorrow to see what i come up with. 121 is a TPS out of range code. 218 and 222 are coil pack failures probably from unplugging the coil packs to test them yesterday. 182 fuel rich at idle or rear 02 sensor fuel control. Could a bad 02 sensor be limiting the fuel to the engine?

Checked heater core pipes. Both pipes are very hot, too hot to touch for more than a second, even with the heat at full blast. I flushed it out both ways and a ton of black fluid came out. Flushed it a few more times and then hooked it back up to the truck. A new heater core is definitely needed, but I don't think that can produce a poor idle.

Listened to the fuel injectors with a stethoscope, I could hear a metallic pinging on each one of them that increased with RPMs. I unplugged each one individually and observed a much worse idle, am I right in assuming they are not the mail culprit?

Disconnected the MAF, cleaned it with brake cleaner and replaced it. There is no dirt or other obstruction in the way.

I unplugged the vacuum line to the fuel rail and i hear the whistle of the vacuum, but the idle changes a little, but not significantly.

I unplugged the vacuum line at the brake booster and the truck immediately died. Plugged it back in and started up fine. Should the truck be able to stay running with that line unplugged?

I noticed on advance autos website they are two different thermostats. One for 180* and one for 192/195*. On rock auto there are even thermostats for 160*. Would a 180* or 160* thermostat prevent the truck from reaching running temperature and cause this issue? Remember, I recently replaced the radiator and drained and filled the coolant. Thats the last repair that I did so maybe they're related?
 
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Sorry for the long posts! I'm trying my best to be as detailed as possible. Im scratching my head at this one, but spirits are still high!

The truck runs fine when cold, then within a few minutes the idle comes down and it starts rumbling and idling poorly. It will run/drive, just not that well. I had it running for a good 20 minutes today explaining to a friend whats happening and the engine stumbled a few times while we were looking at it. It caught itself and came back to idling poorly. Heres what I tested today, I plan on running a fuel rail test and testing sensors with a multimeter tomorrow.

Checked for more KOEO CELs and came up with 121118222218222. Those might be from me messing with the truck the day before, so take them for what you will. I will clear the codes and drive it tomorrow to see what i come up with. 121 is a TPS out of range code. 218 and 222 are coil pack failures probably from unplugging the coil packs to test them yesterday. 182 fuel rich at idle or rear 02 sensor fuel control. Could a bad 02 sensor be limiting the fuel to the engine?

Checked heater core pipes. Both pipes are very hot, too hot to touch for more than a second, even with the heat at full blast. I flushed it out both ways and a ton of black fluid came out. Flushed it a few more times and then hooked it back up to the truck. A new heater core is definitely needed, but I don't think that can produce a poor idle.

Listened to the fuel injectors with a stethoscope, I could hear a metallic pinging on each one of them that increased with RPMs. I unplugged each one individually and observed a much worse idle, am I right in assuming they are not the mail culprit?

Disconnected the MAF, cleaned it with brake cleaner and replaced it. There is no dirt or other obstruction in the way.

I unplugged the vacuum line to the fuel rail and i hear the whistle of the vacuum, but the idle changes a little, but not significantly.

I unplugged the vacuum line at the brake booster and the truck immediately died. Plugged it back in and started up fine. Should the truck be able to stay running with that line unplugged?

I noticed on advance autos website they are two different thermostats. One for 180* and one for 192/195*. On rock auto there are even thermostats for 160*. Would a 180* or 160* thermostat prevent the truck from reaching running temperature and cause this issue? Remember, I recently replaced the radiator and drained and filled the coolant. Thats the last repair that I did so maybe they're related?
You could try pulling the plugs out and see what color they are, brown coloring would indicate cylinder is firing correctly, black would indicate rich condition, white would indicate lean or high temp. Also try temporarily blocking off the EGR from the intake manifold,this could explain loss of power and rough idle.
 


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