Do it yourself information page
This page is for the small tips and tricks that will make for installing and maintaining your TPI more enjoyable.
Setting Minimum Air Idle Speed Serpentine Belt Adjustment Check TPI Manifold Tightening Sequence
Setting TPS idle voltage Fuel Filter information
TPS installation tip Fuel Rail and Components
Idle Air Control Motor Cold Start Injector and Parts
Setting the TPS idle voltage (after new sensor installation and verifying the idle voltage is set correctly). Before you can set the TPS idle voltage you must insure the minimum air idle is set.
NOTE: You must use a high impedance digital volt-ohm meter (typically 10megohms per volt) for this adjustment. Do not use a analog meter as they are normally round 10-20K ohms per volt and will induce a load into the voltage being tested and give a false output reading. And they are not accurate enough for fuel injection work.
Be sure your battery is fully charged, if you have a charging problem, you will need to correct this before you continue.
NOTE: This procedure is only applicable to the 1985-89 with the slotted TPS sensor, the later speed density TPS sensor is a fixed position which is automatically compensating when the power to the ecm is turned on.
Setting Minimum Idle Speed.
First be sure that there is no deposits behind the throttle plates and in the IAC air bypass passage ways. This deposit or "coking" is a mixture of soot and oil that is part of the combustion process. In older engines, a significant amount is oil. If this deposit is enough, it will effectively choke off the air flow to the IAC, causing hesitation and stalling. The best way to clean this is to remove the throttle body from the intake, and using a can of brake cleaner, rags and cotton swabs. Clean in front and behind the throttle plates, remove the IAC and clean the pintle end and the passages on the throttle body. Once this clean, reinstall throttle body. To adjust the minimum air, you must first install a jumper on terminals "A" and "B" on the ALDL. Do this with the key on, engine off. Wait about 30 seconds or so. This will allow the IAC motor to fully extend and close off the air bypass. Without turning off the key, pull the connector off the IAC motor. Start the engine, and let it warm up fully before adjusting. Then it will be at the minimum speed set up. Set the appropriate idle speed specified for your application found in your automotive manual, typically around 450 rpm for the TPI cars. Use the correct torx bit end tool to move he idle screw in or out to achieve the proper minimum air speed. Now you can set the tps to the correct voltage.
Adjusting the idle speed for minimum air is down by turning the idle stop screw clockwise to increase idle speed, counter-clockwise to decrease the speed. The tool is a torx bit end.
TPS Voltage adjustments apply to the 1985-89 vehicles only. The 1990-92 TPI engines use a non adjustable TPS.
To adjust the TPS to its proper voltage, back probe the center (blue) wire with a small pin or paper clip until it bottoms out on the terminal inside the connector. To check for continuity, use a meter or self power continuity checker to see if you have a continuity between the probe wire and the center terminal. The same for the black wire on the connector, as it is the 5V sensor return (common).
Install the tps connector back on the sensor, and hook the positive (red) lead of your digital meter to the probe wire (blue). For meter leads that are point ends instead of clip ends, you will have to purchase or fabricate jumper clips to connect your meter. The negative (black) lead will go to the probed wire (black).
Set your meter up on the lowest scale, which will need to be at least on the hundredths (two placed right of the decimal point) scale.
Turn the ignition key to the "on" position, but DO NOT start the vehicle. If your meter is not showing any voltage, verify it is working by testing your battery voltage, if okay, check you probe wire on the tps connector and make sure it is making contact.
Loosen the screws on the sensor just enough to move the sensor up and down, you should be able to verify this by watching the voltage change on the meter.
Move the sensor to get around .45 to .55V on your meter. Tighten the screws one at a time. You will notice as you tighten one screw, the voltage may go up or down from the desired set point, when this starts to happen, tighten the opposite screw to oppose the voltage drift and continue back and forth until the voltage is in the desired range. This make take a couple of times to get the "hang' of it. DO NOT over tighten the sensor screws!
The final adjustment should result in a stable tps voltage.
Be sure the tang of the sensor's pickup lever is in the position shown, lining up with the tang on the throttle boys actuator lever. Do not over tighten the mounting bolts.
NOTE: The speed density vehicles have a non adjustable TPS
Idle Air Control Motor
When replacing the IAC motor, or reinstalling the old one, be sure that the measurement from the end of the pintle to the IAC motor seat does not exceed 1 1/8" (see Dim. "A" in diagram). Do not install the gasket before measuring and adjustment. If it is longer than that grasp the IAC in your hand with the pintle facing up and with your thumb, rock the pintle back and forth gently while pushing down. If it is jammed and wont move at all, consider replacing it.
Serpentine Belt Adjustment Check
There were two styles of serpentine belt set ups used. The earlier years had a idler pulley similar to the one on the left. The most common, however, is pictured on the right. As the belt stretches over time, the tensioner mark will move clockwise t the right. The right hand picture shows when a brand new belt is installed, the upper mark (arrow) on the stationary side will be aligned with the mark on the pivot side. There is a series of three arrows , then a wide space and an arrow to the far left of the pivot end, which indicated the point the belt needs to be changed.
Also replace the belt if ribbing is coming apart in chucks. Small hair line cracks that run opposing the ribs are okay, large cracks with pieces of the belt missing necessitates replacement.
Fuel Filter information
The fuel filter should be changed at the maximum of two years, sooner in areas where fuel quality may be questionable. Also check the o-rings (red arrows) when replacing the filter, if they are brittle, or show signs of gouging, tearing or stretching, they must be replaced or a dangerous fuel leak will occur.
Fuel Rail and Components Corvette fuel rail shown, F-body fuel intake and return lines on drivers side.
Cold Start Injector and Parts
TPI Manifold Tightening Sequence
Replacing Broken Sensor Connectors