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350 tbi tps adjustment

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chevy gmc tbi Idle air control IAC

My Cookies. Frequently Asked Questions. Forum Rules. Username Post: TPS voltage? I checked it and got 0. I got 5. Just wondering if these perameters are ok. Your numbers seem ok. Dan '16 Chevy Traverse 3. Below is the rule of thumb I use and the most common spec. The voltage should be between. The TBI systems on these trucks looks at the TPS voltage when you go to start the truck and will use that voltage as a reference for zero percent open throttle.

If you have to hold the gas pedal down, AT ALL, to start the truck, this can cause multiple problems. For those of you that are wondering why you are not getting replies to your thread: Did you give the model, year, engine, fuel system type, and transmission information?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.

Most digital volt meters and scan tool displays will not respond fast enough to show this type of a glitch; but some may. If you do find this fault, then the obvious fix is to replace the TP sensor. A stepper motor is a device that moves a predetermined amount per electrical signal it receives by whatever device is controlling it.

The GM IAC has a pintle that extends or retracts into or out of an idle bypass air passage in a throttle body or intake manifold attached to the engine. As it retracts, air flow to the engine is increased as the air passage is opened up.

This air passage is a simple bypass for incoming air to take around the throttle blade. There are many other causes that can make a IAC valve appear faulty. Generally, anything you see over counts should be considered to be a near- or fully-open idle air passage.

On a normal operating engine, it is typical to see high IAC counts or more when the engine is idling cold and during the warm-up cycle. As the engine warms, the IAC counts should decrease. By the time the engine reaches operating temp fully warmed upthe IAC position should drop into the range of about counts in park or neutral. If the scan data you get reports counts lower than this, then that can indicate one or more of the following problems exists:.

Now if you see the scan data reporting IAC position higher than counts on a fully warmed up engine, this could indicate one or more of the following problems exist:.

As you can see, there are many issues other than a faulty IAC valve that can cause a code to set. So before replacing the IAC valve, you should check all of these possible issues first.You don't need a scan tool, since all three of the tests explained in this article are done with a simple multimeter.

Every test has step by step instructions that will make diagnosing the TPS on your GM vehicle a breeze. At the bottom of this page you'll find a complete list of GM cars, pick ups, SUVs and Vans this test article applies to.

How to Reset the Baseline Idle in a GM TBI

Also, in this section you'll find the info you'll need to successfully test and troubleshoot your TPS sensor or code. Like the majority of throttle position sensors on modern fuel injected cars and trucks nowadays, the GM TPS is a three wire sensor. Below are the circuit descriptions of each:. I'm gonna' make one very important recommendation to you when testing the signals of each wire. And that is to not probe the front of the female terminal of the TPS connector.

It's best to use a tool to pierce the wire, such as a wire-piercing probe you can see what one looks like here: Wire Piercing Probe to get to and test the signal.

One last observation, these three circuits go directly to the PCM. So you need to be careful not to short these wires to power 12 Volts or you may fry the PCM. The throttle position sensor gets 5 Volts from the Gray wire and Ground from the Black wire.

Both of these are provided internally from the PCM. Once the car or truck starts and is idling and since the throttle is closed, the TPS sends a base throttle position signal of about 0.

When you step on the accelerator pedal to get the car or truck moving, the throttle opens causing the TP sensor to increase its voltage signal. This is how the PCM knows that the throttle just opened up and that it needs to start injecting more fuel and advancing ignition timing, transmission shift points, etc. As you let go off the gas pedal accelerator pedal the throttle closes and the TP sensor decreases the voltage signal to the PCM and returns to its base voltage signal, till you step on the accelerator pedal to move the vehicle and the cycle begins again.

Pretty simple stuff, no? Well testing it is just as simple. Since you'll be working in the engine compartment, no need to tell you but I'm gonna' tell you anyway to be alert and be very careful. Use common sense and take all necessary safety precautions. All Tutorials: 4. This material may not be reproduced without the author's consent. Page 1 Page 2 Page 3 Page 4.

Really bad gas mileage. Transmission does not shift out of second gear. No power as you accelerate the vehicle. Hesitation when you step on the accelerator pedal. What Tools Do I Need? You will need: A multimeter don't have a digital multimeter?

Need to buy one? A helper. A repair manual for any remove and replace info you may need that this article does not cover. Blue wire.Welcome, Guest. Please login or register. Your ECM has what's called adaptive strategies which allows the ECM to learn known good values which can actually be "off" when there are other underlying issues.

There are many ways in which you can do this. Additionally, step by step procedures are provided for performing the controlled idle speed check and the minimum idle air rate check. It is important that these procedures and specifications be adhered to. An incorrect readjustment with a high minimum air rate will cause the Idle Air Control IAC valve pintle to constantly bottom on its seat and may result in early IAC valve failure.

Controlled Idle Speed Check Before performing this check there should be no codes displayed, idle air control system has been checked and ignition timing correct. The procedures to check the idle air control system can be found in the Light Duty Truck Fuel and Emissions service manual at the following locations: All Truck Engines Except 2. Set parking brake and block drive wheels. Start engine and bring it to normal operating temperature. Check specifications chart at the end of this bulletin for controlled idle speed and IAC valve pintle position counts.

If not within specifications, refer to "Rough, Unstable or Incorrect Idle, Stalling" in Section "2" of the Fuel and Driveability Manual X and review information at the beginning of this check. Check controlled idle speed and perform idle air control system check first.

Start engine and bring it to normal operating temperatures degrees Celsius. Turn engine "OFF". Remove air cleaner, adapter and gaskets. Check that the throttle lever is not being bound by the throttle, Throttle Valve TV or cruise control cables.

Turn "ON" ignition, do not start engine. Wait at least 10 seconds this allows IAC valve pintle to extend and seat in throttle body. With ignition "ON", engine stopped, test terminal still grounded, disconnect IAC valve electrical connector. This disables IAC valve in seated position. Remove ground from diagnostic terminal. If a tool is not available connect a tachometer to the engine. Start engine. With transmission in neutral, allow engine rpm to stabilize. Check rpm against specifications at the end of this bulletin.

If the engine has less than miles or is checked at altitudes above feet, the idle rpm with a seated IAC valve should be lower than values in chart. If the minimum idle air rate is within specifications, no further check is required. If the minimum idle air rate is not within specifications, perform the following procedures: If present, remove stop screw plug by piercing it with an awl, then applying leverage.

The screw is covered to discourage unauthorized adjustments. With engine at normal operating temperature degrees Cadjust stop screw to obtain nominal rpm per specifications with seated IAC valve. Disconnect "Scan" tool or tachometer. Use silicon sealant or equivalent to cover stop screw hole. Install air cleaner, adapter and gasket.

Chris Lucas chevytrucks captkaoscustoms squarebody.Bad TPS? Oct 21, Messages: 12, Likes Received: A TPS is a low-buck part.

Bad TPS? 1991 chevy 350 TBI

You've done enough diagnosis to try a new one. I don't think it will help, but it might. When you unplug it, the ECM goes into "limp home" mode with a pre-set series of tables designed to have the best shot at keeping the engine running until you can get somewhere safe to fix it a garage.

Might be that putting it in limp home mode got you to some point of better runability, esp. If you put in the new TPS and it doesn't help, that doesn't mean you wasted your time. I'd set the timing correctly first, through. Messages: Likes Received: 0. Messages: 1, Likes Received: 0. The TPS is not the only sensor in the equation. The ecm also gets it's information from the coolant sensorr, map and the O2 sesnors as well. All these must give the proper feedback to the injectors to know how much fuel to inject.

The TPS will affect idle as it must be able to see the lowest voltage value in the prom program as well as feedback from the ignition module that correlates with the rpm the ecm must also be able to see. Manually moving the distributor does no good as the ecm will try to correct the timing back to its setting as determined by the program values in the prom.

Fuel pressure also palys a role, so don't overlook this as well weird but true. Having a scanner to be able to look at all the sensors, plus the information to be able to make sense of what you are seeing, will be invaluable. I would suggest this book to have, it has TONS of information. Messages: 58 Likes Received: 0. One was the throttle shaft bushings in the throttle body would wear, same as the throttle shafts would wear on the quadrajets.

This was more common on higher mileage trucks. The other thing we saw was the mainshaft would wear in the distributor, this would cause the engine to idle rough or stall at idle or when letting off the fuel. There should be very little or no play in the shaft. This can cause the timing to jump around which you might see with the timing light.

These are just a few things to check that wouldn't store any faults but could cause your symptoms, hope this helps Last edited: Oct 21, CLogged cat is unlikely. You'd have no power out on the road but it would idle normally. When you unplugged the EGR at idle the idle speed increased? Shouldn't do that. Those EGR passages are known to get clogged up, as is the valve although the valve is not usually the cause. Maybe remove the EGR valve and see how crudded up the passages are underneath.

If it's badly carboned up, it will be fairly obvious. I'm also factoring in your earlier comment about the EGR valve being easy to open with your fingers. It shouldn't be THAT easy. It should take a goodly amount of fingertip pressure.

One more thing came to mind It's an easy check and also an easy fix.Unlike a port fuel injection system, that sprays fuel into the intake manifold runner just above the intake valve, the injectors in this system spray fuel directly into the throttle body above the throttle plate.

The air gap between the throttle body and the throttle plate is calibrated to allow enough air to pass by it for the engine to run at base idle speed. The IAC Idle Air Control valve utilizes the on-board computer to fine tune the idle speed according to engine conditions. Remove the wing nut on top of the air cleaner and lift the air cleaner off the throttle body to access the vacuum lines.

These are attached to the bottom of the air cleaner. Twist and pull the vacuum off of the bottom of the air cleaner and lay the air cleaner aside. Plug the vacuum lines with golf tees or other suitable item. Remove plug over the idle screw located on the right front of the throttle body by using a hammer to drive a punch into the plug and then using the punch to pry the plug out of the throttle body. Discard the plug. Start the engine and let it run until it warms up.

Turn off the engine and leave the ignition key in the "Off" position. Unfold a paper clip and bend it into a "U" shape. In GM vehicles that use this TBI injection, the connector is a black plastic rectangular connector located under the driver side of the dash. The "A" and "B" terminals are located on the top right of the connector.

Unplug the IAC valve located on the passenger side, rear of the throttle body. Start the engine. Insert a T size Torx driver into the Idle adjustment screw that is located behind the plug removed earlier.

Turn off the engine and disconnect the negative battery terminal from the battery using a wrench. Reconnect the IAC valve.

350 tbi tps adjustment

Reinstall the air cleaner and remove the paper clip from the ALDL connector. Reconnect the battery terminal after 5 minutes and test drive the vehicle. This article was written by the It Still Runs 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 Runs, contact us. Step 1 Remove the wing nut on top of the air cleaner and lift the air cleaner off the throttle body to access the vacuum lines.

Step 2 Remove plug over the idle screw located on the right front of the throttle body by using a hammer to drive a punch into the plug and then using the punch to pry the plug out of the throttle body. Step 3 Turn off the engine and leave the ignition key in the "Off" position.

Step 4 Unplug the IAC valve located on the passenger side, rear of the throttle body. Warning Wear safety glasses and work gloves when working around a running engine to prevent serious injuries.

About the Author This article was written by the It Still Runs team, copy edited and fact checked through a multi-point auditing system, in efforts to ensure our readers only receive the best information.Gain extra benefits by becoming a Supporting Member Click here find out how!

Send Private Topic View Profile. Execution time: 0. All times are GMT Pacific. Current time is PM Top. Attach Photos to Posts. Contact Us. My Cookies. Frequently Asked Questions. Forum Rules. Now i installed the TB back in the van and now the idle is super highi connected my aftermarket tach and its idleing at rpm What happens when you do this is the IAC pintle will extend full-closed and stay there until you turn the key off.

At that point the ECM assumes it's closed and has a reference point for any commands it sends to it from there on out. Base gaskets shouln't be glued dwn Check for vacuum leaks at the base Recheck the vacuum lines for integrity and location on the TB.

If U have a vacuum gage use it and any thing lower than about 15" you have a leak. Check the throttle cable for kinks and the attachment to the throttle lever.

Disconnect the cable and make sure the throttle blades are closed all the way against the stop. If the idle drops to normal, you know the IAC isn't functioning.

You don't need a gauge to check for vac leaks, just use a spray as mentioned before. Spray the WD40 around the gasket areas, if the idle changes, there's a leak where you sprayed.

350 tbi tps adjustment

It is very easy to overtighten. On a warm engine, if plugging the inner port makes it idle slower than when the IAC was in place, the IAC was staying open. The IAC is a controlled vacuum leak.

350 tbi tps adjustment

It opens on startup to give you a fast idle. As the engine warms, the IAC closes. At full temp, the IAC is closed no matter what loads are put on the engine. I've not found a TPS that caused a fast idle, but a flooding or rich condition, yes. I don't want to start a fight here but camaro you have it right. When everything is at its optimum, cleaned and working correctly, the idle count will be around When you move the TPS with it at idle, the computer thinks the throttle is getting opened and enriches the mixture, think of it like an accelerator pump if it had a carburetor.

Of course it does. I was simply posting from experience. My experience has been that a normally functioning IAC, or a finger covering the port, gives you the same hot idle speed. I am getting good vacuum per the gauge. I took out the AIC and blocked the hole with my finger, but no change.

It still idles high - any thoughts??? First step for fast idle is check for vacuum leaks.


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