REVISED THROTTLE POSITION SENSOR ADJUSTMENT PROCEDURE
After performing throttle position sensor (TPS) adjustments on production vehicles equipped with a 2.5L L4 EFI engine, the following procedure has proven to be very efficient. This revised procedure should be used instead of the procedure given in the Chevrolet shop manuals.
(1) Remove air cleaner from engine.
(2) Using tool J33047, check minimum idle speed. Adjust if necessary.
CAUTION:
To reduce the risk of fire and personal injury, it is necessary to relieve the fuel system pressure before servicing fuel system components.
To do this:
Remove fuse marked "fuel pump" from the fuse block in passenger compartment.
Crank engine -- engine will start and run until fuel supply is exhausted. When engine stops, engage starter again for 3.0 seconds to assure dissipation of any remaining pressure.
Leave fuel pump fuse out until step #15.
(3) With ignition "off", disconnect electrical connectors from idle air control, throttle position sensor, and injector.
(4) Disconnect throttle linkage, return spring, and cruise control linkage if so equipped.
(5) Disconnect vacuum hoses from throttle body (note routing for proper connection during assembly).
(6) Disconnect fuel supply and return lines at throttle body unit. This will require use of back up wrench to hold fuel nuts on throttle body.
(7) Remove three (3) bolts securing throttle body to intake manifold and remove throttle body.
(8) Invert throttle body and place on a clean flat surface.
(9) Using a 5/16" drill bit, completely through two (2) TPS screw access holes in base of throttle body to be sure of removing the spot welds holding TPS screws in place. Figure 6E2-79 in the 1982 Citation/Celebrity Shop Manual.
(10) Remove two (2) TPS attaching screws and apply Loctite 262 or equivalent to first three (3) screw threads. Reinstall screws and TPS, leaving attaching screws slightly loose.
(11) Lay throttle body unit on intake manifold but do not bolt down.
(12) Install jumper wires between TPS harness and throttle position sensor. (Jumpers may be made from 3", 6" length of 16 gauge wire; three (3) connectors (P/N 12014837), and three (3) connectors (P/N 12014836)).
(13) With ignition "on", use a digital voltmeter to measure voltage between terminals B and C on TPS harness. Voltage should be .525 + .075 in the closed throttle position. Rotate TPS to obtain proper voltage and tighten TPS screws. Recheck voltage reading after tightening screws to be sure adjustment has not changed.
(14) With ignition "off", remove jumpers from TPS and TPS harness.
(15) Reverse removal procedure for TBI installation and with ignition "off", replace fuel pump fuse.
General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.
