High idle problems continue........

[YELLAHEEP]

Still fighting the '96. I've updated my original post in OEM Tech:

http://www.naxja.org/forum/showpost.php?p=244100606&postcount=22

Anyone got any ideas?

 

[ColoradoRaptor]

Did you check Mass air and intake air temp sensors?

 

[thejeepgod]

did you try taking the throttle body off and giving it a good thorough cleaning? sometimes that helps.

 

[Skully]

Still fighting the '96. I've updated my original post in OEM Tech:

http://www.naxja.org/forum/showpost.php?p=244100606&postcount=22

Anyone got any ideas?

Sell it and buy an Audi :jester:

I still fight that demon when it is cold out, new IAC, haven't replaced the TPS yet. Haven't had a problem all summer until it got cold............. did you notice a difference with the weather/temps?

 

[YELLAHEEP]

Did you check Mass air and intake air temp sensors?

For what? From what I've read so far, they don't affect idle or the idle return. Care to elaborate why you think they need checking?

did you try taking the throttle body off and giving it a good thorough cleaning? sometimes that helps.

The throttle body is very clean. I even tried swapping it with a different one from another rig - no change.

 

[YELLAHEEP]

Sell it and buy an Audi :jester:

I still fight that demon when it is cold out, new IAC, haven't replaced the TPS yet. Haven't had a problem all summer until it got cold............. did you notice a difference with the weather/temps?

No real difference with the temps. Just that the idle occasionally drops when the engine is warm, but very irratically and rarely.

 

[swbooking]

Wow, didnt even see your post when I did mine. Ill be trying to take care of my high idle this weekend. Hopefully one of these things will work.

My thread here: http://naxja.org/forum/showthread.php?t=971630

 

[Stang5lgt]

My Mustang did this years ago. I took a piece of tissue and plug the air bypass valve. Stopped the high idle. Mine ended up being a bad air bypass valve(IAC). But plugging yours might help you narrow it down. Cause if still idles up then you know you a have leak some where.

 

[ColoradoRaptor]

For what? From what I've read so far, they don't affect idle or the idle return. Care to elaborate why you think they need checking?

Because I installed the Edge Trail Jammer on my heep and the the new module controls the Mass air and temp sensors, which inturn gives me higher idle on initial startup. I even called the company about it and they informed me that is normal with the new module. I was just trying to think of anything that might help! Not sure but could it hurt to check.....

 

[Frank Z]

Back up the Sensor Bus!! Mass air? on a 4.0L? No such critter. Are you talking about the MAP (Manifold Absolute Pressure) sensor?

Troy,
Have you checked the input voltage to the MAP Sensor?

 

[YELLAHEEP]

Ok, took it for it's first run after the new sensors.........

Now the damn thing won't fire up unless I put the gas to the floor EVERYTIME I wanna start it! WTF? It won't fire at all by just turning the key.

Back up the Sensor Bus!! Mass air? on a 4.0L? No such critter. Are you talking about the MAP (Manifold Absolute Pressure) sensor?

Troy,
Have you checked the input voltage to the MAP Sensor?

Nope, but again, can you tell me why the MAP would be causing these symptoms? Doesn't help much to test the voltage on something that isn't related to the problem - not being a jerk here, just wanna learn the thought process behind the suggestions, ya dig?

 

[ColoradoRaptor]

Back up the Sensor Bus!! Mass air? on a 4.0L? No such critter. Are you talking about the MAP (Manifold Absolute Pressure) sensor?

Troy,
Have you checked the input voltage to the MAP Sensor?

Sensor bus has no reverse!! Mass Air Pressure/Manifold Absolute Pressure.......same darn thing! Sorry, thought he would understand my backwoods terminology and get the picture.:gee:

 

[planefixer]

Troy,
Remove the fuel pump from the gas tank.There should be a short section ( about 2"-3")of rubber hose connecting 2 hard lines on the pump/pickup assembly.Sometimes the rubber hose either cracks or comes loose on one end and causes the symptoms you're describing- ask me how I know.:eyes:
This might not be the problem but its definately something to check.

 

[philip_g]

For what? From what I've read so far, they don't affect idle or the idle return. Care to elaborate why you think they need checking?

If the temp sensor read artificially low wouldn't it lead to running rich and a high idle?

 

[Frank Z]

The PCM receives input signals from various
switches and sensors. Based on these inputs, the
PCM regulates various engine and vehicle operations
through different system components. These components
are referred to as Powertrain Control Module
(PCM) Outputs. The sensors and switches that provide
inputs to the PCM are considered Powertrain
Control Module (PCM) Inputs.
The PCM adjusts ignition timing based upon
inputs it receives from sensors that react to: engine
rpm, manifold absolute pressure, engine coolant temperature,
throttle position, transmission gear selection
(automatic transmission), vehicle speed, power
steering pump pressure (2.5L engine only), and the
brake switch.
The PCM adjusts idle speed based on inputs it
receives from sensors that react to: throttle position,
vehicle speed, transmission gear selection, engine
coolant temperature and from inputs it receives from
the air conditioning clutch switch and brake switch.
Based on inputs that it receives, the PCM adjusts
ignition coil dwell. The PCM also adjusts the generator
charge rate through control of the generator
field and provides speed control operation.
NOTE: PCM Inputs:​

†

A/C request (if equipped with factory A/C)

​

​

† ​

​

A/C select (if equipped with factory A/C)

​

​

† ​

​

Auto shutdown (ASD) sense

​

​

† ​

​

Battery temperature

​

​

† ​

​

Battery voltage

​

​

† ​

​

Brake switch

​

​

† ​

​

CCD bus (+) circuits

​

​

† ​

​

CCD bus (-) circuits

​

​

† ​

​

Camshaft position sensor signal

​

​

† ​

​

Crankshaft position sensor

​

​

† ​

​

Data link connection for DRB scan tool

​

​

† ​

​

Engine coolant temperature sensor

​

​

† ​

​

Extended idle switch (4.0L engine with police

package)
​

​

† ​

​

Fuel level

​

​

† ​

​

Generator (battery voltage) output

​

​

† ​

​

Ignition circuit sense (ignition switch in on/off/

crank/run position)
​

​

† ​

​

Intake manifold air temperature sensor

​

​

† ​

​

Leak detection pump (switch) sense (if equipped)

​

​

† ​

​

Manifold absolute pressure (MAP) sensor

​

​

† ​

​

Oil pressure

​

​

† ​

​

Oxygen sensors

​

​

† ​

​

Park/neutral switch (auto. trans. only)

​

​

† ​

​

Power ground

​

​

† ​

​

Power steering pressure switch (2.5L engine

only)
​

​

† ​

​

Sensor return

​

​

† ​

​

Signal ground

​

​

† ​

​

Speed control multiplexed single wire input

​

​

† ​

​

Throttle position sensor
† Vehicle speed sensor

ENGINE START-UP MODE​

This is an Open Loop mode. The following actions
occur when the starter motor is engaged.
The powertrain control module (PCM) receives
inputs from:​

†​

​

​

​

Battery voltage​

†​

​

​

​

Engine coolant temperature sensor​

†​

​

​

​

Crankshaft position sensor​

†​

​

​

​

Intake manifold air temperature sensor​

†​

​

​

​

Manifold absolute pressure (MAP) sensor​

†​

​

​

​

Throttle position sensor (TPS)​

† Camshaft position sensor signal

​

 

[Frank Z]

ENGINE WARM-UP MODE​

This is an Open Loop mode. During engine warmup,
the powertrain control module (PCM) receives
inputs from:​

†​

​

​

​

Battery voltage​

†​

​

​

​

Crankshaft position sensor​

†​

​

​

​

Engine coolant temperature sensor​

†​

​

​

​

Intake manifold air temperature sensor​

†​

​

​

​

Manifold absolute pressure (MAP) sensor​

†​

​

​

​

Throttle position sensor (TPS)​

†​

​

​

​

Camshaft position sensor signal (in the distributor)​

†​

​

​

​

Park/neutral switch (gear indicator signal—auto.
trans. only)​

†​

​

​

​

Air conditioning select signal (if equipped)​

†​

​

​

​

Air conditioning request signal (if equipped)
Based on these inputs the following occurs:​

†​

​

​

​

Voltage is applied to the fuel injectors with the
ASD relay via the PCM. The PCM will then control
the injection sequence and injector pulse width by
turning the ground circuit to each individual injector
on and off.​

†​

​

​

​

The PCM adjusts engine idle speed through the​

idle air control (IAC) motor and adjusts ignition timing.

IDLE MODE​

When the engine is at operating temperature, this
is a Closed Loop mode. At idle speed, the powertrain
control module (PCM) receives inputs from:​

†​

​

​

​

Air conditioning select signal (if equipped)​

†​

​

​

​

Air conditioning request signal (if equipped)​

†​

​

​

​

Battery voltage​

†​

​

​

​

Crankshaft position sensor​

†​

​

​

​

Engine coolant temperature sensor​

†​

​

​

​

Extended idle switch (4.0L engine with police
package only)​

†​

​

​

​

Intake manifold air temperature sensor​

†​

​

​

​

Manifold absolute pressure (MAP) sensor​

†​

​

​

​

Throttle position sensor (TPS)​

†​

​

​

​

Camshaft position sensor signal (in the distributor)​

†​

​

​

​

Battery voltage​

†​

​

​

​

Park/neutral switch (gear indicator signal—auto.
trans. only)​

† Oxygen sensors

 

[Frank Z]

Just pointing out that the MAP sensor is used in all modes and deserves a second look. That little rubber hose on the bottom can cause incrrect MAP input to the PCM if it's cracked and allowing air in.

 

[YELLAHEEP]

Just pointing out that the MAP sensor is used in all modes and deserves a second look. That little rubber hose on the bottom can cause incrrect MAP input to the PCM if it's cracked and allowing air in.

Now THAT is some useful information. Thanks Frank. On the '96 the MAP is attached directly to the throttle body - I don't think there's a rubber hose on it but I'll double check...(gawd, I've had the damn thing off 5 times, you'd think I'd have noticed it.......) but if it gets it's vacuum by being directly mounted to the TB, I'll also look to ensure it's sealing properly.

Hmmmmm.......

 

[Frank Z]

I don't think there's a rubber hose on it but I'll double check

Yes there is, the 96 is the same as all OBD2 4.0L motors.

 

[ColoradoRaptor]

ENGINE WARM-UP MODE​

This is an Open Loop mode. During engine warmup,
the powertrain control module (PCM) receives
inputs from:​

†

Battery voltage

​

​

† ​

​

Crankshaft position sensor

​

​

† ​

​

Engine coolant temperature sensor

​

​

† ​

​

Intake manifold air temperature sensor

​

​

† ​

​

Manifold absolute pressure (MAP) sensor

​

​

† ​

​

Throttle position sensor (TPS)

​

​

† ​

​

Camshaft position sensor signal (in the distributor)

​

​

† ​

​

Park/neutral switch (gear indicator signal—auto.

trans. only)
​

​

† ​

​

Air conditioning select signal (if equipped)

​

​

† ​

​

Air conditioning request signal (if equipped)

Based on these inputs the following occurs:
​

​

† ​

​

Voltage is applied to the fuel injectors with the

ASD relay via the PCM. The PCM will then control
the injection sequence and injector pulse width by
turning the ground circuit to each individual injector
on and off.
​

​

†​

​

The PCM adjusts engine idle speed through the
idle air control (IAC) motor and adjusts ignition timing.

IDLE MODE
When the engine is at operating temperature, this
is a Closed Loop mode. At idle speed, the powertrain
control module (PCM) receives inputs from:
† ​

​

Air conditioning select signal (if equipped)

​

​

† ​

​

Air conditioning request signal (if equipped)

​

​

† ​

​

Battery voltage

​

​

† ​

​

Crankshaft position sensor

​

​

† ​

​

Engine coolant temperature sensor

​

​

† ​

​

Extended idle switch (4.0L engine with police

package only)
​

​

† ​

​

Intake manifold air temperature sensor

​

​

† ​

​

Manifold absolute pressure (MAP) sensor

​

​

† ​

​

Throttle position sensor (TPS)

​

​

† ​

​

Camshaft position sensor signal (in the distributor)

​

​

† ​

​

Battery voltage

​

​

† ​

​

Park/neutral switch (gear indicator signal—auto.

trans. only)​

† Oxygen sensors
​

​

​

​

​

This is common on most automobiles and thought it was common knowledge as well........I assumed Troy understood open loop/closed loop operation and how ALL sensors play a role in the operation of the modern internal combustion engine. I am no genius nor an ignorant fool and was just passing on something I learned on both my Cobra(MAS) and XJ(MAP). Being at work I did not have the time to find and post the handy information that Frank did(thanks). I could only make quick posts inbetween rounds, moves and shakedowns.... I have been under alot of stress as of late and it does not help when someone takes a shot at my intelligence...... With that said sorry for the earlier rant(missing :lickout, I am just........:banghead::gee:

​