2001 altima engine idle

Do you have any trouble codes?

check for vacuum leaks!

006 Idle Speed Problems Idle Speed Wrong Do you have a professional type scan tool ? If not ,take it to a qualified repair shop .
007 Idle Speed Problems Scan Data for Idle

Throttle position, and or mad air flow sensor. Little pricy but those two sensors control your fuel air mixture causing those issues.

check vacume at manifold vac leak or bad map sensor will create this problem

You have to find the leak and seal it up, hey. It may help to picture where vacuum originates in the engine: As the pistons move down in the cylinders they pull air in from the intake manifold. This creates a pressure drop in the intake, a vacuum that is maintained as the engine is running. New air that is pulled into the intake is measured by the Mass Air Flow sensor mounted in the big boot between the air filter and the intake. If extra air is pulled into the intake manifold from a vacuum leak, uncalibrated air, the computer can figure it out from the oxygen sensors reading in the exhaust-mixture is too lean, so the computer will try to compensate by delivering more fuel, but can't deliver enough, mix is still too lean, so computer sets a code for the vacuum leak.
The intake will have a few vacuum taps with hoses running to engine or car controls that require vacuum to operate. If one of the hoses comes off or has a leak, that is extra air into the intake. Your power brake booster has a large vacuum tap. That may be the problem. With the engine running, pull off that line and plug it, and see if engine speed changes. If the idle drops that may be your leak-a failed power brake booster.
If nothing yet, keep engine running and spray some starting fluid around the mounting area of the intake manifold (maybe the intake gasket has failed and sprung a leak) and listen for a change in engine pitch or speed. The fluid may get sucked into the intake and cause speed to change. If it does, you would need to remove the intake manifold and fit a new manifold gasket.
Also check the big boot from the air filter to the throttle body for tears or loose fit. Good luck, Rev!

You may not have all the things I list. these are things that will make an engine run rich. ECM, 02 sensors, map sensor, mass air flow sensor, vacuum leaks, throttle position sensor, Clogged air filter, Clogged catalitic converter. You have already replaced the injectors and the ECT , so that rules them out. Check for codes. Start with vacuum leaks. Hoses and the intake manifold gaskets. If you need more info let me know. Randy

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.

3.8L Engine (most common) Upper Intake Manifold To Remove:

1. Drain the cooling system.
2. Remove or disconnect the following:
   • Negative battery cable.
   • Fuel injector sight shield.
   • Air cleaner intake duct.
   • Right spark plug wires from the ignition control module and reposition.
3. Relieve the fuel pressure.
4. Remove or disconnect the following:
   • Fuel rail assembly.
   • Brake booster hose from the vacuum source manifold in the upper intake manifold.
   • Exhaust Gas Recirculation Valve (EGR) wiring harness heat shield nut, bolt and the EGR heat shield.
   • Throttle body support bracket upper bolt.
5. Disconnect the electrical connectors from the following:
   • EVAP purge solenoid
   • Throttle Position (T/P) sensor
   • Idle Air Control (IAC) valve
   • Manifold Absolute Pressure (MAP) sensor
   • Mass Air Flow (MAF) sensor
   • EVAP purge solenoid vacuum line from the throttle body.
   • Accelerator and the cruise control cables with the bracket from the throttle body.
6. Remove or disconnect the following:
   • Upper intake manifold bolts and stud.
   • Clean the upper intake manifold bolt threads.
7. Remove or disconnect the following:
   • Upper intake manifold by lifting the back of the intake and sliding the manifold forward from the throttle body support bracket.
   • Upper-to-lower intake manifold carrier gasket from the upper intake manifold.
8. If the upper intake manifold is being replaced, remove the following:
   • Throttle body assembly.
   • Manifold Absolute Pressure (MAP) sensor.
   • Positive Crankcase Ventilation (PCV) valve.
   • Vacuum source manifold.

Upper intake manifold bolt torque sequence (3.8L engine)

To Install:

1. If the manifold was replaced, install or connect the following:
   • Vacuum source manifold.
   • Positive Crankcase Ventilation (PCV) valve.
   • Manifold Absolute Pressure (MAP) sensor.
   • Throttle body assembly.
   • Upper-to-lower intake manifold carrier gasket to the upper intake manifold.
2. Carefully place the upper intake manifold onto the lower intake manifold. Ensure that the alignment pins in the upper intake manifold align with the holes in the lower intake manifold. NOTE: Apply thread lock compound, to the bolt threads before assembly.
   
3. Install or connect the following:
   • Upper intake manifold. Tighten the upper intake manifold bolts in sequence to 89 in lbs (10 Nm)
   • Accelerator and the cruise control cables with the bracket to the throttle body.
   • EVAP purge solenoid vacuum line to the throttle body.
4. Connect the electrical connectors to the following:
   • Mass Air Flow (MAF) sensor
   • Manifold Absolute Pressure (MAP) sensor
   • Idle Air Control (IAC) valve
   • Throttle Position (T/P) sensor
   • EVAP purge solenoid
5. Install or connect the following:
   • Throttle body upper support bracket bolt. Tighten the bolt to 89 in lbs (10 Nm)
   • EGR valve wiring harness heat shield, nut and the bolt. Tighten the nut and the bolt to 89 in lbs (10 Nm)
   • Brake booster hose to the vacuum source manifold.
   • Fuel rail assembly.
   • Right spark plug wires.
   • Air cleaner intake duct.
   • Fuel injector sight shield.
6. Connect the negative battery cable.
7. Fill the cooling system.
8. Inspect for fluid or vacuum leaks.

Lower Intake Manifold (W/O Supercharger) To Remove:

1. Remove or disconnect the following:
   • Upper intake manifold.
   • Generator brace.
   • Drive belt tensioner with the mounting bracket and the heater water bypass inlet pipe.
   • Exhaust gas recirculation EGR outlet pipe bolt from the lower intake manifold.
   • Radiator inlet hose from the water outlet housing.
   • ECT sensor electrical connector.
   • Right upper engine mount strut bracket.
   • Generator brace bracket bolts.
   • Generator brace bracket.
   • Lower intake manifold bolts.
   • Lower intake manifold.
   • Lower intake manifold seals.
   • Lower intake manifold gaskets.
2. If replacing the lower intake manifold, Remove or disconnect:
   • Water outlet housing bolt and stud
   • Water outlet housing
   • Gasket and the thermostat.
   • ECT sensor.
3. Inspect the flatness of inlet flanges.
4. Clean the intake manifold mating surfaces.
5. Clean the intake manifold bolts and bolt holes of adhesive compound.

To Install:

1. If removed, install the ECT sensor.
   • Tighten the ECT sensor to 18 ft. lbs. (25 Nm)
2. If removed, install the thermostat, the gasket, and the water outlet housing.
3. If removed, install the water outlet housing bolt and the stud.
   • Tighten the bolt and stud to 20 ft. lbs. (27 Nm)
4. Install or connect the following:
   • Lower intake manifold gaskets. NOTE: Apply sealer GM P/N 12346286 (Canadian P/N 10953472) or equivalent to the ends of the intake manifold seals.
     
   • Lower intake manifold seals.
   • Lower intake manifold.
   • Lower intake manifold bolts.
   NOTE: Apply thread lock compound GM P/N 12345382 (Canadian P/N 10953489) or equivalent to the two hidden bolts and ensure they are installed.
   
5. Tighten the lower intake manifold bolts in sequence to 11 ft. lbs. (15 Nm)
   
   
6. Install or connect the following:
   • Generator brace bracket.
   • Generator brace bracket bolts. Tighten the bolts to 37 ft. lbs. (50 Nm)
   • Right upper engine mount strut bracket.
   • ECT sensor electrical connector.
   • Radiator inlet hose to the water outlet housing.
   • EGR outlet pipe to the lower intake manifold.
   • EGR outlet pipe bolt to the lower intake manifold. Tighten the bolt to 21 ft. lbs. (29 Nm)
   • Drive belt tensioner.
   • Generator brace.
   • Upper intake manifold.
7. Inspect for leaks.

Lower Intake Manifold (W/ Supercharger) To Remove:

1. Disconnect the negative battery cable.
2. Drain the cooling system.
3. Remove the supercharger.
4. Remove the thermostat housing.
5. Remove the EGR pipe at the intake manifold.
6. Disconnect the electrical connection at the temperature sensor.
7. Remove the intake manifold and gaskets.

NOTE: The coolant bypass tube will release from the intake manifold when the manifold is removed.
To Install:

1. Clean the gasket sealing surfaces.
2. Install the intake manifold gaskets.
3. Align the coolant bypass tube with the opening in the intake manifold and install the manifold. Tighten the bolts to 11 lb ft (15 Nm).
4. Install the electrical connector to the temperature sensor.
5. Install the EGR pipe to the intake manifold.
6. Install the thermostat housing.
7. Install the supercharger.
8. Fill the cooling system.
9. Connect the negative battery cable.

Don't waste your time. Have the intake manifold gaskets (upper and lower) replaced. Check all vacuum lines for leaks. Clamp all vacuum hose connections.
Do NOT replace any sensors unless the computer codes indicate.
THIS WILL FIX YOUR PROBLEM!

Intake Manifold REMOVAL & INSTALLATION 1.9L SOHC Engine

1. Before servicing the vehicle, refer to the precautions in the beginning of this section.
2. Properly relieve the fuel system pressure.
3. Drain the coolant system.
4. Remove or disconnect the following:
   • Negative battery cable
   • Air cleaner fresh air hose
   • Positive Crankcase Ventilation (PCV) valve hose
   • Fuel line from the rail
   • Throttle cable from the throttle body
   • Throttle cable bracket nuts
   • Fuel injector electrical connectors
   • Throttle Position (TP) sensor electrical connectors
   • Idle Air Control (IAC) valve electrical connectors
   • Manifold Absolute Pressure (MAP) sensor electrical connectors
   • Exhaust Gas Recirculation (EGR) valve electrical connectors
   • Heater hose from the intake manifold outlet
5. Position the wiring harness over the brake master cylinder
6. Remove or disconnect the following:
   • Intake manifold support bracket bolt
   • Label the vacuum line for proper assembly
   • Drive belt
   • Power steering pump
   • Upper intake manifold bolts
   • Evaporative Emissions (EVAP) canister purge valve solenoid vacuum hose
   • Brake booster vacuum hose
   • Lower intake manifold bolts
   • Intake manifold
   To install:
   
7. Thoroughly clean all gasket mating surfaces. Be careful not to damage or score the aluminum surface. If replaced, use Loctite® 290, to seal the new PCV valve inlet tube into the manifold. NOTE: Refer to Section 1 of this manual for the intake manifold torque sequence illustration. The illustration is located after the Torque Specification Chart.
   
8. Install or connect the following:
   • New gasket and manifold. Torque the nuts in sequence to 22 ft. lbs. (30 Nm).
   • Power steering pump. Torque the fasteners to 27 ft. lbs. (38 Nm).
   • Drive belt.
   • Heater hose and install the manifold support bracket bolt. Tighten the bolt to 22 ft. lbs. (30 Nm).
   • Lubricate the male ends of the fuel lines with a few drops of clean engine oil, then connect the fuel supply and return lines.
   • Fuel line(s) in the retaining bracket. Torque the mounting screw to 36 inch lbs. (4 Nm).
   • Throttle cable to the throttle body and attach the accelerator cable bracket. Torque the bolts to 22 ft. lbs. (30 Nm).
   • Reposition the wiring harness and connect the wiring and vacuum hoses to their original locations. The harness leads to the TP sensor and EGR solenoid must be routed between the intake manifold runners.
   • Negative battery cable
9. Fill the coolant system.
10. Prime the fuel system by cycling the ignition ON for 5 seconds and OFF for 10 seconds a few times without cranking the engine.
11. Start the engine, check for leaks, and repair if necessary.