Have you heard of Noid lights? You unplug the fuel injector and plug these in and they will light up if the injector is getting power. This might give you a better hint. There are also lights that go inbetween the spark plug and wire. Between these two items you may be able to narrow down the problem to a specific system. I believe that your car has a coil pack. Some of these engines have problems with the crank trigger. I believe it is located on the back side of the motor. If you decide to change it, be careful. I have heard of them breaking into two pieces and becoming a big problem.
My problem was solved when I repaired my 4 wd activation dash switch. The switch was contacting on 2WD & 4HI at the same time. The front differential activation is vacuum activated possibly creating a tug of war that didn't actually engage it but drained off vacuum from the engine? A theory at best but stumbbled across it because I knew the switch wasn't working properly I repaired it and low and behold rough idle disappeared and all is good for 3 weeks running.
REPLACED IDLE AIR YOU HAVE TO ADJUST ITS DIMENSION. MEASURE FROM THE TIP OF PINTLE TO THE MOUNTING FLANGE.YOUR DISTANCE HAS TO BE 1 1/8 INCH.IF NOT ADJUST PINTLE BY PRESSING IT 1 1/8 INCH. YOU NEED TO RESET IDLE BY CYCLE THE IGNITION KEY ON FOR TEN SECONDS THEN OFF FOR TEN SECONDS TO RESET THE VALVE.START THE ENGINE ALLOW IT TO IDLE FOR FIVE MINUTES TURN THE ENGINE OFF FOR THIRTY SECONDS THEN START THE ENGINE AGAIN AND CHECK THE IDLE OPERATION.
Sounds like you have a vacuum leak. When the engine is cold the leak is there but as the engine warms up the parts start to expand thus closing the gaps and sealing the leak. I had this problem on my personal vehicle and it turned out to be lower intake gaskets.
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I tried to post 2 hours ago and the site wouldn't let me so this will be in 2-3 parts ok ! (1) please clean out your throttle body with fuel injection cleaner and if your using no name branded fuel stop now this has no detergents in it, and you will find a brown varnish inside the throttle plate ,after doing this also spray around the intake manifold and the egr evap egr sensors and hoses if the rpm's change you found a leak next post in comments
If your vehicle has one, and I think it does, check your EGR system. If the egr valve is full of carbon, it can be partially open, creating a vacuum leak. If the egr valve solenoid is bad, it could be opening the valve at the wrong time, also creating a vacuum leak. Unplug the egr vacuum hose, plug the open end of the hose and start it and see what it does. A picture of the egr is below.
doesnt mean its the computer system--that cud be an egr valve-dirty throttle body or idle motor------ignition components like ol plug wires or failin fuel pump------even vaccuum leaks
Something is probably leaning out the mixture when you open the throttle. It seems that any ignition issues have been ruled out.
So, check the following: fuel filter clogged, low fuel pump pressure, the fuel pressure regulator could be stuck at the idle setting, the EGR valve could be stuck open, faulty throttle position sensor (TPS) or circuit, faulty manifold absolute pressure (MAP) sensor, faulty or dirty manifold air flow (MAF) sensor, faulty intake air temperature (IAT) sensor, and an air leak into the intake duct or manifold between the MAF and the throttle body. I think if the intake manifold gasket had a leak, it would be misfiring at idle.
Ask the shop if any of the above checks have already been accomplished. I'll bet most of them have, but one may have been overlooked.
Go to the parts store and get a noid light for your truck, plug it into the injector electrical and turn the engine over to see if there is electrical pulse, also check the fuel pressure, the pump needs 9-13 psi with the engine running. you know if there is no pulse your going to need to check the wireing first. let me know
Before servicing the vehicle, refer to the Precautions section.
Relieve the fuel system pressure.
Drain the cooling system.
Remove or disconnect the following:
Negative battery cable
Supercharger
Thermostat housing
Exhaust Gas Recirculation (EGR) tube at the intake manifold
Engine Control Temperature (ECT) sensor
Intake manifold
To install:
Install or connect the following:
Intake manifold with new gaskets. Torque the bolts, working from
the center out, to 11 ft. lbs. (15 Nm).
ECT sensor connector
EGR tube to the intake manifold
Thermostat housing
Supercharger
Negative battery cable
Refill and bleed the cooling system.
Run the engine and check for leaks and proper engine operation.
VIN K Engine
Before servicing the vehicle, refer to the Precautions section.
Disconnect the negative battery cable.
Drain the cooling system.
Relieve the fuel system pressure.
Remove or disconnect the following:
Fuel injector sight shield
Air inlet duct
Spark plug wires from the right side
Manifold Absolute Pressure (MAP) sensor
Vacuum lines from the intake manifold
Fuel lines
Fuel injector electrical connectors
Fuel regulator vacuum line
Fuel rail from the intake manifold
Exhaust Gas Recirculation (EGR) heat shield
Throttle cable bracket from the cylinder head mounting bracket and
the throttle body cables
Throttle body support bracket
Upper intake plenum and gasket
Thermostat housing
Electrical connector from the Engine Coolant Temperature (ECT)
sensor
Drive belt tensioner assembly
EGR valve outlet pipe
Lower intake manifold
Fig. Exploded view of the intake manifold and related
components-3.8L (VIN K) engine
Install or connect the following:
Intake manifold using new manifold gaskets. Torque the bolts in
sequence to 11 ft. lbs. (15 Nm); then, re-torque to 11 ft. lbs. (15 Nm).
EGR valve outlet pipe
Drive belt tensioner assembly. Torque the tensioner bolts to 37
ft. lbs. (50 Nm).
Electrical connector to the ECT sensor
Thermostat housing
Upper intake plenum. Torque the intake plenum bolts to 88 inch.
lbs. (10 Nm).
Throttle body support bracket
Throttle cable bracket to the cylinder head mounting bracket and
the cables to the throttle body lever
EGR heat shield
Fuel rail. Torque the fuel rail bolts to 88 inch. lbs. (10 Nm).
Fuel lines
Fuel regulator vacuum line
Fuel injector electrical connectors
Vacuum lines to the intake manifold
MAP sensor
Spark plug wires
Fuel injector sight shield and air inlet duct
Negative battery cable
Refill and bleed the cooling system.
Run the engine and check for leaks and proper engine operation.
could bea few things. Excessive moisure, low fuel pressure, Faulty coil pack, spark plugs gap or wires. Have you changed any of those at all? Let me know
Have you heard of Noid lights? You unplug the fuel injector and plug these in and they will light up if the injector is getting power. This might give you a better hint. There are also lights that go inbetween the spark plug and wire. Between these two items you may be able to narrow down the problem to a specific system. I believe that your car has a coil pack. Some of these engines have problems with the crank trigger. I believe it is located on the back side of the motor. If you decide to change it, be careful. I have heard of them breaking into two pieces and becoming a big problem.
Wow you have replaced a lot of stuff. Lets go back to the Fuel pump. When you replaced it did you replace the hose between the pump and the sending unit. These are common for splitting. Have you hooked up a fuel pressure gauge to check what pressure you have? It should be real close to 13 psi and should raise to at least 18 or 19 when you pinch off the return line.
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