This is a discussion on Surging idle, before and after new IAC valve within the General Help forums, part of the LSx Technical Help Section category; I have a surging problem, about every 3 seconds the car revs slightly. Forum Rules. Remember Me?Trane s8x1
What's New? Page 1 of 2 1 2 Last Jump to page: Results 1 to 20 of Add Thread to del. Thread Tools Show Printable Version. Surging idle, before and after new IAC valve. I have a surging problem, about every 3 seconds the car revs slightly. There is a ticking coming from the intake, do not know if it is related or not. Share Share this post on Digg Del. Sounds like a vacuum leak possibly. Check all the vacuum hoses for cracks or even being disconnected.
If you can't narrow it down, you can spray a little starting fluid around different areas, and when the idle raises, check that area. I've tried that before and nothing happened.
Another thing you might check is the wiring for the sensor. When I was cammed sometimes my car wouldn't grab an idle after I disconnected the battery. Key the car to the ON positiong. Don't start it. Wait 30 seconds, key off. Plug the sensors back in and start the car. When you're adjusting the TB set screw to get your IAC counts into the right range you have to do this each time.
Perhaps yours is slightly off and just needs to be relearned. Another thing to consider is that new parts do not always equate to good parts. Tried resetting the iac and tps. Cleaned the iac port, and plug. Cant see any physical damage in the wires. IAC counts?? In process. Posted from Android App. Originally Posted by JacobLS1. Like a tech 2? I can probably use one at my brothers work.
It set off a p What kind of info? Found this.Commonly called an idle air control IAC valve or idle speed control ISC valve, this device is used on many cable-operated throttle bodies to regulate the engine idle speed. This process is completed by regulating airflow through a bypass circuit around the throttle plate to increase or decrease idle speed.
Increasing the volume of air that flows through the bypass circuit around the throttle plate increases idle speed. Reducing the bypass airflow decreases idle speed. The engine control module controls and monitors this process and can command the fuel mixture to compensate for the airflow.
When we refer to the engine idle speed, this is the speed in revolutions of the engine when the driver's foot is not activating the throttle. While the throttle plate is closed, the main intake passage for the engine is closed off so a bypass circuit is necessary to keep from choking the engine.
When the engine's idle speed is above or below the predetermined range in the computer's program, the computer commands the valve to either increase or decrease the bypass air flow. Additional sensor inputs from the coolant sensor, brake switch and vehicle speed sensor may also be used by the computer to regulate idle speed according to various operating conditions.
Tip : If the engine speed is too high, too low, or stallingthe problem may not be the idle speed control system, but an engine vacuum leak. Check for vacuum leaks first to rule out this possibility. Considering a vacuum leak, a common condition is to find the IAC valve extended all the way out closed position. This usually means the engine has an air leak and the engine computer is trying to bring the idle speed back down by closing the idle air bypass circuit.
If there is an open or shorted circuit in the idle air control solenoid, driver circuit, or the idle speed is out of range, it will usually set one or more fault codes and turn on the Check Engine light.
If the light is on, you must plug a scan tool into the diagnostic connector and read out the codes that set the light. These vehicles use an angle sensor on the throttle pedal to calculate throttle input.GM Idle Air Control IAC Function, Diagnostics and Repair
The engine computer will then activate a small motor on the throttle body which also has a position sensor so the computer can match the throttle pedal angle to the throttle plate angle. An idle malfunction here may require cleaning or the replacement of the throttle body as well as the use of a professional scanner to reset the system.
Warning : The difference between throttle body cleaner and brake cleaner is the throttle cleaner does include a bit of lubricant for the moving components of the throttle body.
DO NOT use throttle body cleaner on brake system hardware. Step 1: Gain access to the IAC valve. Consult the vehicle service manual for the location of the IAC valve on your vehicle.
Step 2: Disconnect IAC valve. Step 3: Start the engine. Start the engine and observe how the vehicle reacts. Where a vehicle may have previously been stalling after start-up, disabling the IAC valve my open the bypass circuit and cause the vehicle idle to raise when the valve is disabled.
Step 4: Reconnect the IAC valve.Remember Me? What's New? Page 1 of 2 1 2 Last Jump to page: Results 1 to 20 of Thread Tools Show Printable Version. If you go to the end of the log, the TPS is at zero and the car is in park. My IAC count is arount What should it be at and how do I adjust this?
It should be at with a cammed car. Your throttle position will now be reset to 0 degrees and about. Any higher can put you into the wrong fueling cell. HP Tuner tuned by me. I don't think there's anything wrong with IAC at It's less than half of full scale. The thing that will bring IAC down aside from more bypass air is more spark and proper fueling. Fueling is going to be bugged by O2 sensor fidelity cold from headers and airflow VE fidelity, tending to overfuel after a cam swap.
But there's nothing wrong with IAC counts in itself. Originally Posted by jimmyblue. IAC counts are adjusted by moving the set screw in the throttle body or enlarging the hole in the throttle body blade.
Allowing more airflow into the engine by enlarging the hole or opening the blade with the set screw will reduce IAC counts. The trick to using the set screw is having to reset your TPS after you make the changes. Opened it up, and a lot better. Originally Posted by ws6ick.
How to Check an Idle Air Control Valve
Mine is not surging. If you say IAC count is good then I am leaving it alone. How do I get my scanner to read the throttle position voltage? Last edited by ws6ick; at AM.
Signs and Symptoms of a Bad Idle Air Control Sensor
I disagree with that, my opinion is that the only thing you want out of the set-screw is to keep the blade from binding under vacuum. If the throttle body is not physically munged then barely-off-seat for the blade should just give you the right volts. TPS voltage is not zeroed with a reset, it will keep a higher voltage. Steve Williams TunedbyFrost. Originally Posted by Frost.
If you have much of a cam, and you don't adjust for ish counts at hot idle and in some conditions lessyou won't have enough airflow at cold-start and cold idle conditions.
That offset proves to be important. SCR is high 11s I have it at about 20 counts at degF. There is not enough blade offset and IAC to satisfy the car under about 65degF at cold start. By high degrees, it will take a little pedal to get it going.Remember Me? What's New? Results 1 to 12 of Thread Tools Show Printable Version.
If I manually adjust the IAC, and just leave it unplugged, the car idles and drives just fine. I have reset the TPS using the unplug, power on, power off, plug in, method. Readings and voltages are good. This happened to me last year, and I just unplugged the damn IAC and tuned idle with the throttle blade using the set screw, blade is undrilled.
I rebuilt the car over the winter, put it in, and it was fine the first several hundred miles. All of the sudden, RPM idle, no tuning changes.
I'm quite confident there are no vacuum leaks; I've checked with propane, verified with my gauges, and the idle behavior when I bypass the IAC is just as expected and if I plug the IAC hole with a rubber stopper, the car will, obviously, not run.
Again, this happens with 3 IACs. Nobody at all, eh? I'm going to be changing the car to E85 and am planning on starting with my factory tune to redo it all I was "learning" during a good portion of my previous tuning, and I'd like to start fresh on some of the things I'm sure I've done wrong. I'm assuming that I should be making sure my VE table is solid in the idle area? Is there anything else that could be causing this from a software control perspective?16 dpo symptoms
If you log idle spark advance I can bet it is negative pulling timing when you unplug the IAC. This means either the throttle body blade has a hole larger then stock, or you have a vacuum leak some where. That where the Idle Spark Dvance pulls timing to bring idle to match desired idle rpm.
Another thing, it could be the blade is being kept slightly open Log TPS Voltage, it should be around. Have you tried adjusting the TB screw to close it a little?
When the IAC counts go to 0 and the idle speed is still high, it means the IAC motor has completely closed and there is still too much air entering the engine causing the high idle speed. With engine at operating temp, adjust the TB screw to close it until it wants to die, then backup a little. Make sure it doesn't get stuck in the closed position by opening it by hand. Blake, did you ever get this problem resolved?
Torquer v. Originally Posted by nmcqueen Last edited by digitalsolo; at PM. I have had this same exact issue for a year now. Cant seem to find a fix for it. Any ideas? At the suggestion of another member, I just replaced my TPS then did the reset and that cured the problem.
Idles normal now. You should try it. I'm having this same issue, i have a new tps and iac. Car is a bone stock 99 trans am. Sometimes idles perfect and drops back to idle when slowing down then other times idles right upto rpm and sits there and has cruise control when driving.The job of the TPS is to tell the computer what the position of the throttle is.
This sensor is vital in helping the computer determine if the throttle is closed or open; or how fast the throttle is opened or closed. The throttle position sensor is a simple potentiometer that uses ground and 5-volt reference inputs to produce a varying output signal depending on the position of its detection arm or shaft.
If this sensor is out of adjustment or is failing, the result could be stalling, idle surge, flat throttle response, hesitation, or erratic engine operation. Most of the TP sensors you find on stock Fiero engines are the adjustable type while those found on newer GM engines are usually non-adjustable. If the TPS on your engine is adjustable, it must be set correctly in order for the computer to function normally.
Some throttle position sensors are adjustable. You will also need the proper tool to loosen the retaining screws. If you have a scan tool, all you need to do is pull up the TPS voltage data.
If you are using a digital volt meter, then voltage will need to be measured across the blue and black wires going to the TPS.
If this seal is broken, moisture can corrode the connections to the TPS and create all sorts of problems. Once you get your TPS voltage display up, turn the ignition on but do not start the engine.
The voltage with closed throttle should be between 0. If the voltage you get is not within spec, loosen the TPS retaining screws and adjust as necessary. Normal voltage reading for wide open throttle WOT is above 4. There are trouble codes that are associated with the TPS. One c ode will set if the TPS voltage is too high when the computer expects to see it lower. Another code will set if the TPS voltage is lower than the computer expects to see. The TPS code for low voltage is the most common and will usually set if the TPS is out of adjustment or the sensor has failed.
There are circumstances that could occur with a failing throttle position sensor that may not set a trouble code.
One of the most common symptoms of a failing TPS would be a tip-in hesitation or stumble when you apply throttle to take off from a stop. Unfortunately this type of failure is not easy to diagnose without the proper tool — a digital waveform scope.IAC valve mechanisms often begin to malfunction after a few hundred thousand miles, but can become dirty and clogged in far less time. IAC-related no-start conditions usually only occur on older vehicles with fully electronic drive-by-wire, DBW throttles.
Most IAC failures manifest themselves as a start-and-stall condition. Generally speaking, the engine will catch and run for a second or two, stutter and die. IAC-related start-and-stop conditions can be easily differentiated from fuel-related issues; during IAC-related stalling, applying throttle in light pulses may prolong engine failure, but will not prevent it. Applying throttle while facing fuel-related failure will result in immediate stalling.
When rapidly decelerating, the driver lifts his foot from the throttle pedal and applies the brake. Once the driver's foot is clear of the throttle, the engine's TB valve completely shuts. In the case of a malfunctioning IAC, rapidly shutting the throttle pedal will starve the engine of air, resulting in a stall either while decelerating or after coming to a stop.
A very cold engine needs more fuel than a warm engine, which is important to know while diagnosing the problem. An obstructed or stuck-shut IAC will result in a rich air-fuel ratio at idle, so the engine will start very easily while cold and then die suddenly after a slight puff of black tail-pipe smoke.Django chatbot template
Because most IACs break while in the open position, a "stuck-shut" diagnosis is usually indicative of one that's simply clogged. An intermittent stalling condition is one in which the vehicle might start fine, act as though it's going to die, idle smoothly and then die completely.
Alternatively, the vehicle may run fine most of the time, but stall periodically and then restart with a bit of difficulty. Intermittent stalling almost always indicates a dirty or clogged IAC. This article was written by the It Still Works team, copy edited and fact checked through a multi-point auditing system, in efforts to ensure our readers only receive the best information.
To submit your questions or ideas, or to simply learn more about It Still Works, contact us. Deceleration Failure When rapidly decelerating, the driver lifts his foot from the throttle pedal and applies the brake. Weather Factors A very cold engine needs more fuel than a warm engine, which is important to know while diagnosing the problem.
Intermittent Stalling An intermittent stalling condition is one in which the vehicle might start fine, act as though it's going to die, idle smoothly and then die completely. About the Author This article was written by the It Still Works team, copy edited and fact checked through a multi-point auditing system, in efforts to ensure our readers only receive the best information. Photo Credits fuel valve image by Luis Bras from Fotolia.Last Updated: March 29, References Approved. This article was co-authored by our trained team of editors and researchers who validated it for accuracy and comprehensiveness.
There are 13 references cited in this article, which can be found at the bottom of the page. This article has been viewedtimes.
Where the heck is the Idle Air Control valve
Learn more The idle air control valve — also known as the "idle speed control valve" — regulates the idle speed of your engine. This is controlled by the engine's computer.
Sometimes parts go bad, which results in your car idling strangely or stalling. Check to see if your idle control valve is functioning properly before attempting to replace it. To check if an idle control valve is working properly, start by turning on your engine and letting it run for a minute or 2. Then, when it's at an idling speed, take note of the RPMs in your car. Next, turn the engine off and disconnect the idle control motor under your hood.Aha music firefox
Once it's disconnected, tuck the wire out of the way, restart your car, and wait a minute or 2 before checking your RPMs. If your RPMs are the same both times, your idle control valve isn't working. For tips on how to check an idle air control valve in a GM or Ford car, read on!
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