Question about 1988 Chevrolet Blazer
Please check out this link for proper instructions and diagrams with step by step help as some else who was facing the same problem and how he replaced it and dit it himself.
Have you ever noticed a loud hum and/or whine (whining) coming from your engine bay? Or more specifically your intake area? Well, more often than not, this is due to a dirty IAC (Idle Air Control) Valve. Since everyone is always asking about it, hopefully this will help.
My engine was making the loud hum / whine noise. AutoZone wanted $131.99 for a new part. and it's $50 deductible against my extended warranty, so I wanted to fix this myself. I purchased a can of Electrical Parts cleaner, the non-residue type, drove home and let the engine cool. Here's a pic of where the IAC Valve is located under the hood:
Two 10mm bolts to remove, and unclip the electricals
Turn the valve to notice two chambers. Inside one of them you will see a spring. Inside the other, you will probably see a bunch of dirt coating what should be an exposed sensor. Spray the Electrical parts cleaner liberally, directly into the opening, and watch until the liquid coming out of the valve is clear (white). Set the IAC on a towel or clean surface and allow any other liquid to drain and the sensor to fully dry. Here's a picture of a clean IAC valve
And don't forget to clean the sensor below the black snap off cap on the side of the IAC valve:
After allowing to dry, replace the IAC and start your truck. You should allow the engine to warm up for a few minutes and the computer will re-learn how much air to allow into the engine at idle.
I experienced a much LOUDER whine after doing this for the remainder of the day, but I only allowed the liquid to drain for about 2 minutes. The whine hasn't returned in two days since, so I'm guessing the liquid cleaner wasn't completely drained when I replaced the IAC Valve.
for pictures on how exactly it should be done click the above link.
Posted on Oct 11, 2008
You have done allot but have you checked the fuel pressure? Have you changed the fuel filter, this sounds like a low pressure concern, either the pump or a dirty fuel filter, also have you run a test for trouble codes from the fuel injection computer, also called the ECU or PCM?
Posted on Oct 11, 2008
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The Idle Air Control (IAC) is a bi-directional motor driven by two coils. The purpose of the IAC valve is to control engine idle speed, while preventing stalls due to changes in the engine load. The IAC valve, mounted in the throttle body, controls bypass air around the throttle plate. The PCM controls engine idle speed by adjusting the position of the IAC motor pintle. The PCM pulses current to the IAC coils in small steps (counts) to extend the pintle into a passage in the throttle body to decrease air flow. The PCM reverses the current pulses to retract the pintle, increasing air flow. This method allows highly accurate control of idle speed and quick response to changes in engine load. If RPM is too low, the PCM will retract the IAC pintle, resulting in more air being bypassed around the throttle plate to increase RPM. If the RPM is too high, the PCM will extend the IAC pintle, allowing less air to be bypassed around the throttle plate, decreasing RPM.
Fig. Typical Idle Air Control (IAC) valve components
During idle, the proper position of the of the IAC pintle is calculated by the PCM based on the battery voltage, coolant temperature, engine load and engine RPM. If the RPM drops below a specified value, and the throttle plate is closed (TP sensor voltage is between 0.20-0.74), the PCM senses a near stall condition. The PCM will then calculate a new IAC pintle position to prevent stalls.
If the IAC valve is disconnected and reconnected with the engine running, the idle RPM will be wrong. In this case, the IAC has to be reset. The IAC resets when the ignition switch is cycled ON and then OFF . When servicing the IAC, it should be disconnected or connected with the ignition switch OFF in order to keep from having to reset the IAC valve.
The position of the IAC pintle affects engine start up and the idle characteristics of the vehicle. If the IAC pintle is fully open, too much air will be allowed into the manifold. This results in high idle speed, along with possible hard starting and a lean air/fuel ratio. A Diagnostic Trouble Code (DTC) may set. If the IAC pintle is stuck closed, too little air will be allowed in the manifold. This results in a low idle speed, along with hard starting and a rich air/fuel ratio. Again, a Diagnostic Trouble Code (DTC) may set. If the IAC pintle is stuck part way open, the idle may be high or low and will not respond to changes in engine load.
As with most all engine control sensors used in your vehicle, a thorough and proper test can only be performed by a qualified technician using a scan tool to read the data stream from the PCM. There are a few items a non-professional should check before taking the vehicle to a qualified technician for diagnosis and repair.
Check for a poor connection at the PCM or IAC motor. Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals and poor terminal-to-wire connection. Inspect for a damaged wiring harness, especially if heavy work has recently been performed (intake manifold removal, engine removal, etc.) where the throttle body has been disturbed. Inspect for a restricted air intake system. Check for a possible collapsed air intake duct, restricted air filter element or foreign objects blocking the air intake system. Inspect the throttle body. Check for objects blocking the IAC passage or throttle bore. Excessive deposits, especially on high-mileage engines, can build up in the IAC passage and on the IAC pintle. Excessive deposits can also build up on the throttle plate, so check for a sticking throttle plate. Check for vacuum leaks such as disconnected hoses, leaks at the EGR valve and EGR pipe to the intake manifold, leaks at the throttle body, faulty or incorrectly installed PCV valve, leaks at the intake manifold brake booster hose connection, etc.
REMOVAL & INSTALLATION
Fig. The Idle Air Control (IAC) valve is mounted on the throttle body-3.8L (VIN K) engine shown, others similar
NOTE Before installing a new IAC valve, measure the distance that the valve is extended. The measurement should be made from the motor housing to the end of the valve cone (pintle). The distance should be no greater than 1 1 / 8 inch (28mm). If the pintle is extended too far, adjustment is required, otherwise damage may occur when the IAC valve is installed. Adjust the IAC valve by compressing the pintle to achieve the correct length.
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