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High idle help

OldMan89

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Tennessee
Vehicle Year
1989
Make / Model
Ford ranger
Transmission
Manual
Good evening everyone! Hope everyone is staying warm! My 89 ranger (2.3l out of a ‘92 and a 5 speed) has been running a little weird lately and I’m really stumped.
Now it’s cold here in Tennessee so that might be some of my issue but I’ll take any advice I can get!

when I cold start it, after the initial engine rev, it backs down to 1100 rpm and holds. I assume this is just to warm the motor faster?Every-once in a while it will idle up to 1500 rpm and hold no matter the weather and no matter how warm the engine is. I have to turn the engine off and back in to get it to go back down. This truck has always idled at 600rpm. I replaced the IAC this week but don’t have but about 20 miles in it by since. But I’ve noticed now it idles at 800-900 rpm… and I find this strange. Could it be egr? Intake leak? Dirty throttle body? Bad O2 sensor? I’ve checked for vacuum leaks and can find none.

I also have an intermittent problem where when I press the clutch coming to a stop, the Rpms shoot too 1500 and hold until I take off again…. That one I really have no clue.

and while I’m here I’ll go ahead and ask… if I replaced my blower motor resistor but my blower motor still only works intermittently, could it be a bad blower??

thanks so much in advance and if any more info is needed just ask. I can get back with you asap!
 


RonD

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All gasoline engines need to be Choked when cold started, fuel injection didn't change that

Choking, for gas engines means Rich fuel mix and high idle
A Choke plate was/is used on carb engines, closes off the air intake which causes more fuel to be Sucked from the Jets, the Rich mix, and a cam on the throttle linkage held throttle open a bit more for higher idle

For EFI the Computer opens injectors longer for the Rich mix, and opens IAC Valve a bit more for higher idle

When you turn on the key the computer opens IAC Valve all the way, so engine should REV to 1,500 anytime you start it
Then computer starts to close it and if cold 1,100 RPMs is about right
As engine warms up computer keeps closing IAC Valve until warm engine "target" RPMs are set
For a 4cyl engine 600RPMs would be too low, 700-750 maybe for a manual trans
Thats because 4cyl engines only fire a cylinder every 180deg, so they vibrate ALOT under 700rpms, even 700 can be shaky
V6s or V8s have no issues with lower RPM idles

Anyway back to topic
The computer sets the Choke based on coolant temp reading from the ECT sensor, this is different that the dash temp gauge sender
ECT has 2 wires, I would change it just on speculation, although you can test it with OHM meter and pan of boiling water

The computer uses the IAC Valve, idle air control valve, to set idle RPMs, these can be cleaned
Ford uses a true Solenoid IAC Valve, so it should only be replaced by a Motorcraft or Hitachi brand IAC Valve, others are hybrid step/stepper motor valves so can act up, kind of like what you have now

And yes, change the PCV Valve, it should be changed every 2 years, or 1 year on high mile engines
PCV Valve is a "controlled" vacuum leak, so if it gets too much oil inside it, the "control" part gets iffy, lol
Shaking a PCV Valve and feeling the weight move, means you have good arm strength, never meant anything else regardless of what your Dad or Grandad said :)
But you can soak it in gasoline then blow it out, then use it a bit longer if it seems OK
 

OldMan89

New Member
Joined
Jul 20, 2021
Messages
9
Reaction score
2
Points
3
Location
Tennessee
Vehicle Year
1989
Make / Model
Ford ranger
Transmission
Manual
All gasoline engines need to be Choked when cold started, fuel injection didn't change that

Choking, for gas engines means Rich fuel mix and high idle
A Choke plate was/is used on carb engines, closes off the air intake which causes more fuel to be Sucked from the Jets, the Rich mix, and a cam on the throttle linkage held throttle open a bit more for higher idle

For EFI the Computer opens injectors longer for the Rich mix, and opens IAC Valve a bit more for higher idle

When you turn on the key the computer opens IAC Valve all the way, so engine should REV to 1,500 anytime you start it
Then computer starts to close it and if cold 1,100 RPMs is about right
As engine warms up computer keeps closing IAC Valve until warm engine "target" RPMs are set
For a 4cyl engine 600RPMs would be too low, 700-750 maybe for a manual trans
Thats because 4cyl engines only fire a cylinder every 180deg, so they vibrate ALOT under 700rpms, even 700 can be shaky
V6s or V8s have no issues with lower RPM idles

Anyway back to topic
The computer sets the Choke based on coolant temp reading from the ECT sensor, this is different that the dash temp gauge sender
ECT has 2 wires, I would change it just on speculation, although you can test it with OHM meter and pan of boiling water

The computer uses the IAC Valve, idle air control valve, to set idle RPMs, these can be cleaned
Ford uses a true Solenoid IAC Valve, so it should only be replaced by a Motorcraft or Hitachi brand IAC Valve, others are hybrid step/stepper motor valves so can act up, kind of like what you have now

And yes, change the PCV Valve, it should be changed every 2 years, or 1 year on high mile engines
PCV Valve is a "controlled" vacuum leak, so if it gets too much oil inside it, the "control" part gets iffy, lol
Shaking a PCV Valve and feeling the weight move, means you have good arm strength, never meant anything else regardless of what your Dad or Grandad said :)
But you can soak it in gasoline then blow it out, then use it a bit longer if it seems OK
thank you so much! This jogged my memory and I do have a KOER code 21 for ECT out of range. I’ll change that out and see what happens. I did put a cheap IAC on it but I still have the factory one. I cleaned it out in the fall but didn’t spend much time on it so I will re visit. PCV was changed last summer. And I need to change the plugs and wires. Thank you for the in depth explanation! Your a blessing!
 

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