Engine idles rough, codes P1131, P1151, P0102

Good morning.

The upper intake is behind the IAC.

When you disconnect the IAC wires, does the engine run about 500 rpm?

Roy

1151/1131

P1151
Descriptor
Lack Of Ho2S-21 Switch, Sensor Indicates Lean
Probable Causes
Air Induction System Leak after the Mass Air Flow (MAF) Sensor
Camshaft Timing Incorrect
Cylinder Compression Incorrect
Diaphragm or EGR Vacuum Regulator (EVR) Leaking
Engine Oil Dipstick Incorrectly Seated
Exhaust Gas Recirculation (EGR) Valve Malfunction
Exhaust Leak Before or Near the Heated Oxygen Sensor (HO2S)
Fuel Injectors Leaking and or Contaminated
Fuel Pressure Excessive
Fuel Pressure Low or Insufficient Fuel
Fuel Pressure Regulator Leaking
Gasket Leaking
Harness or Heated Oxygen Sensor (HO2S) Short to Ignition Switched Power (VPWR)
Heated Oxygen Sensor (HO2S)
Heated Oxygen Sensor (HO2S) Circuit Open or Shorted
Oil Overfull
Poor Mating Terminals and Wiring or Corrosion
Positive Crankcase Ventilation (PCV) System
Powertrain Control Module (PCM) Damaged
Vacuum Leaks
Vapor Recovery System
Water in Harness Connector

102

P0102
Descriptor
Mass Air Flow (Maf) Circuit Low Input
Probable Causes
Closed Throttle Indication In Throttle Position Sensor (TPS) System
Intake Air Leak Near Mass Air Flow (MAF) Sensor
Mass Air Flow (MAF) Circuit Open to Powertrain Control Module (PCM)
Mass Air Flow (MAF) Circuit Shorted to Ground
Mass Air Flow (MAF) Return Circuit Open to Powertrain Control Module (PCM)
Mass Air Flow (MAF) Sensor Damaged
Mass Air Flow (MAF) Sensor Disconnected
Power or Ground Open to Mass Air Flow (MAF) Sensor
Powertrain Control Module (PCM) Damaged
Voltage Power Open to Mass Air Flow (MAF) Sensor

The engine runs between 500 and 600 rpms with IAC connected. Disconnect the IAC and it will not idle. It starts then shuts off. I forgot to mention I can hear the sucking of air coming from the firewall. I just cannot pinpoint it.

The engine should idle at 500-600 with it disconnected. That could be a base idle adjustment or the throttle body plate is filthy with carbon.

Yes, you need to track down the vacuum leak. Once you find that and repair it, re check the idle.

Roy

https://www.2carpros.com/articles/throttle-actuator-service

https://www.2carpros.com/articles/stall-at-idle

Could there be a vacuum leak at the upper intake itself? The vacuum leak sounds like it's right at or just past the IAC. I can hear a lot of air moving at the leak. Are there any vacuum lines behind the IAC? I know there are some wires but it is so tight back there it is hard to distinguish what they are? I appreciate your help and will continue to look.

Yes, it could be the upper intake. If you have some 2+2 or Brake Kleen, you can spray it around and see if the idle gets better.

Roy