The engine is idling at 1100 rpms. I cleaned the throttle body and changed the iac valve with no change to the idle. Am I missing something?
Run fault codes to see what you are missing
SOURCE: high idle 1997 Madza 626 4 cylinder auto transamission
The PCM controls idle speed to ensure good driveability. The PCM will only attempt to maintain the desired idle speed when it “knows” the throttle is closed. A throttle switch or the TPS input is used to determine when the throttle is in the idle position. Motors and solenoids are used by most PCM’s to control idle speed. Many PCM’s are programmed to attempt to control the idle speed by adjusting spark timing and then by controlling the idle speed actuator. Some computers of the early 80's did not control idle speed.
SOURCE: idle at 1500 to 2000 rpm
Most likely the throttle body gasket (between the throttle body and the intake manifold) is leaking.
SOURCE: 2001 taurus dohc codes 171
There is a large vac line coming straight down from the throttle body that goes to the PCV system. See if it has a hole in it. It is likely sucking air.
Hello my name is autoteck21 sounds like you dealing with one of two things. #1 Either you have a vacuum leak in one of your hoses or your vacuum box at the worst case one of your vacuum control
solenoid. #2 Your idle air control module (under your throttle body.)
To test #1 take a can of brake clean or carb/choke cleaner and in small 2-3in areas spray little spots while engine is running listen too your idle for any changes (you will here the differences) if so there's your leak.
To test #2 find the little connector (2 wire) under your throttle body (when standing in front of your car lower front side under intake pipe hose clamp)
Yes, having no thermostat can cause the car to run fast as it will still be set in it's "warm up" mode and will be injecting a richer mixture of fuel/air into the cylinders. There may be an additional cold start injector that just works while the engine is cold. You will probably use more fuel like this. It's not a great idea to run with no thermostat anyway because you get uneven hot and cold spots around the engine which is bad for it. Cheers
Testimonial: "many thanks ben ive renewed themostat and problem solved "
OPERATION
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.
TESTING
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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