been reading the forum for awile having problems with high idle
I have a 1993 4-wheel drive ranger with a 3.0 5-speed started ideling high
have no codes or check engine light
this is what I have done
1 repaired all vac leaks
2 cleaned throttle body and replaced gasket
3 cleaned idle air control and replaced gasket
4 smoke check for vac leaks
5 replace idle air control w/new gasket
idles at 12 to 15 hundred rpm more often than not as high as 2800 to 3000
other times it will idle at 900 to 1000 rpm
don't know what else to do any help or advice is appreciated

 

Couple of things to do first.
After engine is warmed up, unplug IAC Valve's wires, idle should drop down to 500 or engine may even stall, either is OK it means no vacuum leak, but see next....

If idle stays above 800 then shut off engine, open throttle all the way by hand and disconnect throttle cable and Cruise control cable(if so equipped)
Restart engine, if idle is now less than 600 or engine stalls then you have a cable holding open the throttle.
If idle goes up and down the throttle return spring is broken or weak


If idle is 500 or engine stalls on first test then computer is opening IAC Valve too much, this could be a problem with the IAC valves Step Motor or with the computer itself.

Unhook the battery for 5 minutes, then hook it back up, this will cause the computer to reboot and hopefully relearn the correct idle.

The computer has a factory programmed cold idle and warn idle
Cold idle is based on temp, idle should be about 1,200 on chilly morning
Warm idle for manual transmission is 600-650.

On a '93 3.0l Computer gets RPMs from TFI module on distributor, well from the hall effect sensor inside the distributor via the TFI module.
And if that wasn't working you would have no spark or fuel.

 

found I had a bad iac replaced same is better--- but when driving and push in clutch the idle will be 1500 to 3200 will drop off in approx. 20 sec or so to 1500 have fixed all vac leaks and run vac ck on system by putting vac gage on line from brake booster to manifold vac holds at 191/2 to 20 inches of vac while engine is running I do not have a dist I have a coil pack ANY IDEAS ON THIS HIGH IDLE----- in cali wont pass smog

 

RPM should stay high when you are moving and push the clutch in, it saves on gas and lowers emissions, BUT..............if you leave the clutch in RPMs should start dropping in 5 to 10 seconds, not 30 seconds.
And while speedometer is above approx. 5mph the idle RPMs should always be above 1,000, when stopped RPMs should drop to 650-700 assuming engine is warmed up.
I have read that Ford can reprogram theses settings if they go off kilter.

After engine is warm and you unplug the IAC valve what does the idle do?
As said above it should drop to 500 or engine should stall.

If it doesn't then there could be IAC valve issue(new just means "never tested") or a cable is holding throttle open, or there is a vacuum leak.

 

I unplug iac on warm engine the idle will go from 1500 to about 750 i have already done a smoke test on vac system shows no leaks i have also did vac ck and system (with engine warm) will idle with a 19.5 to 20 inch vac which also says no vac leak i think i am right on this trk idle is notmally about 850rpms

 

Then something is holding open the throttle plate, disconnect gas pedal cable and cruise cable, if so equipped.

Look for a screw on the throttle linkage, it is an "anti-diesel" screw, but someone may have thought it was an idle screw, fuel injected engines can't use an idle screw, no Jets like a carb had.

try to figure out why the idle is so high, when IAC valve is closed all the way(unplugged)

3.0l with manual trans should idle at 650, automatic 750.
In gear with AC on, an auto might jump to 800, manual 700 may be

 

I have backed out anti-deisel screw so that it is not touching
Have unhooked throttle cable
Have made sure throttle plate is shut all the way
No vac leaks found
Can get to idle at 850 but not consistantly
It will idle at 12 to 1500 after about 1 1/2 min it will sart a real slow idle down but only to 850
This is after warm up
About ready to shoot this thing in the head and put it out of my misery

 

When you first turn on the key computer will open IAC valve all the way for starting, so when engine starts idle should jump up above 1,400
Then computer will check the ECT(engine coolant temp) sensor to get coolant temp, if cold the idle should drop to approx. 1,200, the colder it is the higher the RPMs, this should only take a few seconds.
As coolant warms up the computer will lower the RPMs accordingly, this can take 5 to 8 minutes depending on outside temperature.
Target idle for computer should be under 700 for a manual transmission, my '94 4.0l idles at 650, this is programmed in the computers software, computer uses IAC valve to get that target idle.

But it can only do that if engine idle is lower than 650 when IAC valve is closed all the way.

The warm idle level is set by minimum operating temp of 190degF, thermostat rating, if thermostat is stuck open or ECT sensor is reporting an incorrect lower temp it could set a higher idle, but since the only idle control the computer has is the IAC Valve unplugging it would reveal that if idle dropped to 500.
And you would notice that the dashboard temp gauge wasn't getting up to above 1/3 to almost 1/2 like it should.


IAC valve sits on an air passage that goes from in front of the throttle plate to behind throttle plate, this passage is a "controlled vacuum leak", the IAC valve is what controls the amount of air allowed to pass thru the opening.

IAC Valve uses a Step or Stepper motor, this is a "digital" electric motor, it will have over 100 "steps" the computer can use, each "step" holds the motor at XXX degrees of rotation.
The computer sends a voltage pulse continuously to the IAC valve to hold the Step motor at a specific position which holds the valve part open a specific amount.
When you unplug the wires from the IAC valve the step motor has no "control pulse" so will go back to 0, which closes the valve part.

My suggestion would be to remove the air plenum tube from the intake, look inside it and find the hole/passage that the IAC Valve uses, it should be near the IAC Valve.
Unplug the IAC valve and start the engine, warm engine would be better.
Use a rag or wear a glove and plug that passage while engine is idling, if idle doesn't change then passage is closed.
If idle changes then IAC Valve is not closing or not sealing the passage like it should, could be a bad gasket as well.


Also thought of the TPS(throttle position sensor), this sensor just monitors where the driver's foot is on the gas pedal.
It is connected to the throttle plate shaft to do this, and if installed incorrectly it could hold the throttle plate open a bit.

 

where is the ect at--- if it can cause it to idle high I would like to know how to check it or replace it--- if so is there anything special I need to know
dash board gage gets to 1/2 way that's where it rides --- mine will not run with air plenum tube off to do test you suggested[plug off iac hole] once again how to ck etc
I have already checked tps [voltage wise and checked for hanging up]

 

Engine should run with MAF disconnected, that is actually a test of the MAF, so not running with air tube off seems odd to me.
Unplug MAF first and try to start engine, if it starts unhook air tube and do the test.

ECT is a 2 wire sensor, located on lower intake by thermostat housing or on a metal bypass tube on the front of engine.
There is also a 1 wire sender for the temp gauge that looks similar, that ain't it!

Computer sends ECT sensor 5volts on 1 wire, if engine is cold sensor will pass approx. 3volts back to computer on the other wire, as coolant warms up, return voltage will drop.
Fully warmed up return voltage should be under 1 volt, as low as .5v.

The computer has a timer that comes on when engine is started, if ECT sensor isn't showing lower and lower voltage as engine runs computer will turn on the CEL, usually within 5 minutes of starting a cold engine.
So most like not the problem, if there is no CEL, especially if temp gauge shows at least 1/2.

TPS, like IAC valve, is a Learned device.
TPS should show below 1volt(.60-.99) when throttle plate is closed and above 4.5v when throttle plate is wide open, computer learns closed voltage.

 

I have had same problem... SOLUTION was the "Crankshaft Position Sensor". When it is worn, it begins to do this high idling, initially only when the engine warms up. Then later as it wears more, it will start the high idling sooner and sooner. I bought one from my local Advance Auto parts versus Rockauto mainly in case I hade get a quick replacement. I have need to replace my elcheapo one 3 times in the last 2 years!!! One other chat room highly suggests getting the Motorcraft/Ford OEM version which costs more, but that is what I would do. Fortunately for me I got a lifetime replacement with my elcheapo and I have gotten free replacements. Replacing it is very easy and quick... just one securing bolt at base of shaft in block, and then it comes straight out and of course unplug electrical connection. AND ADDITIONAL NOTE is that if you are low on coolant, it will cause the sensor to overheat which will cause the high-idling too, but it is the Crankshaft Sensor that is causing the issue often. THIS IS A COMMON 3.0 engine issue

Another note... make sure you put the shaft back in the same way it came out. I take the sensor off the top first and note the position of everything.. maybe take a picture... then make sure when you replace the shaft it is pointed just like it was before you took out the bad one. BEFORE TAKING OFF THE SENSOR notice where the sensor head is pointing... it should be ~75 degrees toward the drivers side of the truck... like at 2-3 o'clock when looking from front of truck as per shop manual.

Hope this helps

 

Good info.

Never heard of that one before, CKP(crank position) sensor and high idle RPMs, it reads a 36 tooth wheel on the Crankshaft, well 36 teeth minus 1 tooth, there is 1 tooth every 10 degrees for 360deg(full circle), missing tooth is where #1 piston is at TDC, this is how computer times the spark and injection, and is also the RPM counter.

If the sensor is not working then you have a no start, this is one of the only sensor that can cause a no start.

As said, haven't run into an intermittent CKP sensor before.

 

checked throttle plate while I had air tube off it is shutting al the way plugged off iac port on throttle body no change in idle speed still at 850 and no vac at iac port I will change cps where is it located at what does it take to get it out

 

Here is a pretty good video on how to change it. (https://www.youtube.com/watch?v=upNyLdSADiI) It is really easy. It is located at the center rear, top of the engine. The securing bolt is a 10 or 12 mm bolt with a LARGE washer that places pressure on the base of the CPS so that it stays in the block and does not move. NOTE. take note of the position of the rotor in the assy so that you put it back in, in the same position you took it out.... no skipped teeth. I ACCOMPLISH THIS by taking the actual sensor off the top of the CPS... it has 2 6.5 mm screws holding it down and then comes straight up and off (it could be a little stuck).... and then you can note the position of everything so that when you put the new one in it is facing exactly the same. I take a picture to compare the locations after the new one is in.

 

well I replaced ckp sensor still no change any more ideas

 

Call Ford dealer with VIN in hand and ask if there is a TSB regarding high idle and requires a computer software up grade

 

I got ahold of ford about a tsb said there were none
very next day[today] check engine light comes on just got back from having codes read po171 and po174 lean both banks. I did not find anyvids on utube that shows me how to change upper and lower intake gakets for a 1998 3.0 or is there something else I need to do first many thanks for the help so far should I change fuel filter

 

generally both banks having lean code means upper intake vacuum leak, low fuel pressure or MAF sensor issue.

Lower intake leak would only be on 1 bank, so code would be 171 OR 174 not both

Engine is not actually running Lean, just FYI.
Computer gets air data from MAF sensor, uses 14:1 Air:Fuel ratio for the amount of fuel it needs to add to the air that is coming in past the MAF sensor.
After adding the fuel computer gets the O2 data for lean or rich burning of fuel, too much Oxygen is Lean, too little Oxygen is Rich, O2 reads Oxygen level not fuel.
Computer then adds more or less fuel to get the O2 sensors to show "good" burn, not too lean and not too rich.
If computer has to add too much fuel over the 14:1 calculation it will set lean code for that bank, or both if they both needed the extra fuel.

This code tells the driver that the 14:1 calculation is off, that's all it means.

MAF sensor issue, low fuel pressure, vacuum leaks could all set 171/174 codes.
And of course a computer issue, but lets keep a good thought :)

 

Changed upper and lower intake manifold gaskets changed every hose( except hard plastic ones) now it really runs bad upper intake says to torque to 89in lbs torque to 40in lbs feels like the 4 center bolts are going to pull out any ideas
Thanks in advance

 

Tried to go to 89in lbs first bolt broke got it out have to find new one. I am right on my torque specs at 89 In lbs for upper intake manifold bolts. Please advise