Question about 1990 Toyota 4Runner

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1990 4Runner, 3.0 L engine, won't hold idle, wants to stall, no power. Replaced Mass air flow valve sensor, replaced fuel pump, distributor cap and rotor, plugs. It has good fuel flow but only runs well above 1500 rpm and when warm. It surges when cold. What other components could I change. 250,000 miles on engine.

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Have you looked at your idle air control valve What is it? This is an electrically driven valve that allows additional control over the throttle at idle Where is it located? The IAC is located on or adjacent to the throttle body and consists of a small device held on by two bolts with an electrical connector.
How does it work? When the throttle is closed the throttle plate closes off any air from the intake manifold. In order to stop the engine from stalling due to lack of air the IAC opens a small valve allowing air to pass from the air ducting to the intake manifold. Often the IAC components consist of an air inlet port in the inside wall of the throttle body, immediately in front of the throttle plate, with a similar exit port behind the throttle plate. Connecting the two ports is a motor driven valve. When the valve is opened air effectively by-passes the closed throttle plate to maintain the engine at idle. The IAC also augments the throttle when additional power demands are put on the engine such as steering.


Symptoms of faulty IAC

  • Poor starting: If the IAC fails to open or the inlet/exit ports are clogged shut with carbon the engine may start and then promptly stall. The engine can be kept running by pressing the accelerator. However any additional demand on the engine such as power steering or putting the car into drive (automatic) will cause the engine to stumble badly and often stall.
  • Engine cut out: Even with the engine warmed when the vehicle is stationary such as at a red light the putting of the transmission into of 'drive' to pull away before the accelerator is pressed can cause the engine to stall. (Note this differs from the TPS fault which causes engine stall due to the accelerator being pressed too quickly)

How to check? Physically remove the IAC but keep the electrical connection to it. Temporarily block off the now open ports on the throttle, turn the engine on and examine the IAC valve action in response to additional loads (power steering inputs etc). The valve should open and close according to demand.

How to fix? If the motor of the IAC has failed then replace the IAC. If the valve is gummed closed by baked oil and carbon then clean it thoroughly with carburetor choke cleaner spray and a cloth. Similarly if the entry and exit ports on the throttle body to the IAC look blocked again clean them out thoroughly.

Posted on Jun 03, 2010

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  • engine king Sep 21, 2011

    check your idle air control valve or throttle position sensor. if it is just an idle problem then one of these is probably the problem. the best way to check is to unplug the iac electrical connector. if you idle smooths out after a few seconds of being unplugged then this is the problem. there will probably be no need to buy a new one because you can just remove the iac valve and clean it. if you find that it is not the iac valve then locate your throttle position sensor and tap on it lightly while the vehicle is running. the throttle position sensor some times gets stuck and simply tapping on it will clear it up sometimes. if this doesnt work then unplug the throttle position sensor electrical plug and listen for a correction of idle. One of these two sensors are more than likely the problem. if not, then you may have a problem with a valve

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Leaky vacuum hose, faulty idle air control valve, can affect the idle bad 02 sensors can make it to rich or lean, in your case too lean. A dirty throttle body can plug up the sensors as well.

Posted on Jun 03, 2010

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1 Answer

Engen problem and missing


Sir, your question is not very clear, but I will still try to post a solution here. Engine missing could be due to any problem in fuel system, ignition system, engine or ECM as well.

LOW ENGINE IDLE SPEED (Poor idling):
-Throttle body (do the cleaning and idle speed learning)
-A /C signal circuit
-Fuel pump control circuit
-Fuel pump
-Intake system
-P C V valve (clogged or open) and hose

ROUGH IDLING:
-Cylinder Compression
-Ignition system (Igniters, spark plugs, wiring harness)
-Spark plug fouled, gap too wide or too short. (1.00-1.1 mm)
-Fuel injector circuit
-E C M power source circuit
-Fuel pump control circuit
-Fuel pump (required pressure 44 psi - 49 psi)
-Throttle body (cleaning)
-Intake system
-P C V valve and hose
-Air fuel ratio sensor
-Heated oxygen s ens or
-Mass air flow meter
-Idle hunting
-Throttle body
-Intake system
-P C V valve and hose
-Air fuel ratio sensor
-Mass air flow meter

HESITATION/ POOR ACCELERATION:
-Fuel pump control circuit
-Fuel pump
-Spark plug
-Ignition system
-Fuel injector circuit
-E C M power source circuit
-Mass air flow meter
-Throttle body (do cleaning)
-Intake system
-Valve timing
-Cylinder Compression


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I have a 2001 GMC Jimmy with a 4.3L V6. Replaced the intake manifold, spark plugs, spark plug wires, distributor cap and rotor. When going to start it, it will start but ruff idle and stall. I checked to...


This could be air or fuel, if you are getting a mass air flow code then make sure there are no vacuum leaks around the intake also if the distributor is in wrong depending on how far off it is it could run but will run bad and will stall out, did you mark the distributor housing and also where the rotor was pointing as it is very important that the distributor rotor is point in the same spot as it was coming out if not then you will need to set the engine at top dead center and then locate the #1 cap location and install the dist rotor to be pointing to that wire,,top dead center is with #1 cylinder at the top of the compression stroke, make sure before you do that that there are no leaks try to keep it running by holding the gas pedal while someone look for a vacuum leak, you will hear a hissing sound for a vacuum leak, good day.

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1 Answer

VERY ROUGH IDLE NO EXCELERATION


Try a few if these ideas...

Priority Action Part Type Cause
1 Inspect Spark Plug Fouled, Damaged, or Broken Spark Plug(s).
2 Inspect Hose (PCV) Clogged or Collapsed PCV Hoses.
3 Inspect Wireset Worn, Damaged or Faulty Spark Plug Wire(s).
4 Inspect Distributor Worn, Damaged or Faulty Distributor.
5 Inspect Catalytic Converter Clogged or Faulty Catalytic Converter.
6 Inspect Fuel Pump Low Fuel Pressure.
7 Inspect TimingSet Slipped TimingChain or Worn TimingGear(s).
8 Inspect Knock Sensor Improperly Connected or Faulty Knock Sensor.
9 Inspect M.A.P. (Manifold Absolute Pressure) Sensor Faulty M.A.P. Sensor.
10 Inspect Throttle Position Sensor Faulty or Incorrectly Connected Throttle Position Sensor.
11 Inspect Mass Air Flow (MAF) Sensor Damaged, Loose, or Faulty Mass Air Flow Sensor or Circuit.
12 Inspect Air Cleaner Temperature Sensor Damaged or Faulty Air Cleaner Tempature Sensor.
13 Inspect Fuel Injector Pressure Regulator Faulty Fuel Injector Pressure Regulator.
14 Inspect Piston Ring Set Worn or Broken Piston Rings.
15 Inspect Timing Specification Incorrect Ignition Timing.
16 Inspect Fuel System Pressure Incorrect Fuel Pressure Being Delivered to Carburetor or Fuel Injection System.
17 Inspect Fuel Filter Clogged or Dirty Fuel Filter.
18 Inspect PCV Valve Plugged or Damaged PCV Valve.
19 Inspect Valve Burned, Worn, or Sticking Exhaust Valves.
20 check idle stop solenoid - if faulty, could cause rough idling
21 inspect distributor cap/rotor - if burnt, could cause loss of acceleration

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Hello,
your problem appears to be the idle control motor located on the air intake manifold it is a small motor that goes bad quite often. Other items that can cause this is a bad /clogged air filter or a tune up (spark plugs and wires), or clogged fuel injectors. to clean the injectors you can buy a container of fuel system cleaner and pour it into the gas tank and as you drive it cleans the system.

Once the fuel system is cleaned via a tankful of cleaner & gas then the idle controller motor would be next on the list to be replaced.

Good Luck !
Rich Lilja

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Engine power loss


Inspect Wireset Damaged, worn, or deteriorating spark plug or coil wire(s). in this list u will find a answer to ur problem Shaun 2 Inspect Spark Plug Fouled, damaged or broken spark plug(s). 3 Inspect Fuel Filter Clogged or dirty fuel filter 4 Inspect Distributor Worn, loose or incorrectly adjusted distributor. 5 Inspect Distributor Cap Loose or cracked distributor cap 6 Inspect Distributor Cap And Rotor Kit Loose, cracked, or worn distributor cap and ignition rotor. grey_line.gif 7 Inspect PCV Valve Plugged or damaged pcv valve. grey_line.gif 8 Inspect Air Filter Restricted or clogged air filter. grey_line.gif 9 Inspect Catalytic Converter Clogged, damaged, defective or faulty catalytic converter. grey_line.gif 10 Inspect Automatic Transmission Improperly adjusted kickdown cable adjustment or internal transmission problems. grey_line.gif 11 Inspect Fuel Pump Improperly functioning fuel pump or circuits. grey_line.gif 12 Inspect MAP Sensor Improperly connected or faulty m.a.p. sensor. grey_line.gif 13 Inspect Mass Air Flow Sensor Improperly connected or faulty mass air flow sensor. grey_line.gif 14 Inspect Throttle Position Sensor Faulty throttle position sensor or throttle position sensor circuit. grey_line.gif 15 Inspect Timing Specification Incorrectly adjusted engine timing. grey_line.gif 16 Inspect Fuel System Pressure Incorrect fuel pressure being delivered to carburetor or fuel injection system. grey_line.gif

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