How To Adjust the Throttle Position Sensor
By Chuck Westbrook
Tools Needed
(1) A high impedance voltmeter (preferably a digital) with one
alligator clip.
(2) A small safety pin opened up to form a 90 degree angle.
(3) Depending on the type of fasteners that hold your TPS in place;
the tools needed to loosen and retighten them. Mine had bolts with a combination Philips
screw driver and 7MM nut head. Some have only a screwdriver head and need a 90 degree bend
screwdriver or screw driver tips for a ratchet drive. These screw driver head only bolts
are the pits and most owners have replaced them after removing the throttle body. Make
sure your engine ground points are clean and tight. An additional grounding strap for the
throttle body or extension manifold to the firewall is a good idea to keep your engine's
electrons flowing freely.
The throttle-body, firewall side with TPS
TPS Connector Leads (4 lined up vertically) and Required
Voltages:
(1) 2nd from top (green wire with red stripe), this goes to the 3F
ECU connector. Closed throttle +V range is 0.75 to 1.25. Fully opened throttle +V range is
4.8 to 5.0.
(2) Bottom (black wire with green stripe), this goes to the 3G ECU
connector. Closed throttle +V range is 0.1 to 0.7. Fully opened throttle +V range is 4.2
to 4.6.
Procedures
(1) Start and run engine until at normal operating temperature and
the fast idle cam is at normal idle position.
(2) Turn off the engine.
(3) Remove the AWS hose that connects to the throttle body curved
inlet pipe and to the AWS solenoid behind the throttle
body. This is to give you easier access to the TPS bolts.
(4) Remove the hose from the pressure sensor on the firewall and
tuck it down out of the way. This also gives you more
room to access the TPS bolts. If extra room is still needed, remove
the pressure sensor from the firewall.
(5) Totally loosen the bottom TPS bolt and partially the top one.
(6) Connect the negative volt meter lead to a good ground point. I
used one in the diagnostic connector since it goes to the ECU.
(7) Insert the safety pin point into the TPS 3F or 3G connector (see
above) between the rubber weather seal and the wire. Using the alligator clip, attach the
positive voltmeter lead to the safety pin head. Select the appropriate voltmeter range. Be
sure not to accidentally ground this lead!
(8) Turn the ignition on without starting the engine. If there isn't
a voltmeter reading, adjust the safety pin until it does have a reading.
(9) Record the voltages for closed and fully opened. Open the
throttle fully by hand, not the accelerator pedal.
(9a) Verify that the voltages increase as the throttle is opened.
Look for "dead" spots or voltage fluctuations as you slowly open the throttle.
(10) Do the same for the other TPS connector point.
(11) If any of the four voltages are out of range, loosen the top
TPS bolt and adjust the TPS until all four are in range. If all four can't be adjusted
correctly; then either the TPS is bad, the fast idle cam is still engaged, or the idle set
screw on the throttle is way off normal position.
The following note is for PFS PMC users only
NOTE: The further the idle set screw on the throttle is adjusted
down (throttle opens up), the higher the low end readings will be if the high ends are
good. That's because the arc of throttle movement will be shifted towards the high end.
Try and imagine the geometry of the throttle rotating shaft connected to the TPS which is
nothing but twin variable resistors like a volume control on a stereo. Even though I had
all four in their voltage ranges, my PMC would not read WOT. I adjusted the TPS just until
WOT occurred, and then rechecked the four voltages. They were still good but shifted
towards the high end of their ranges. WOT is only needed for vent learn. My 3K stumble
wasn't bad until forcing my TPS to show WOT on the PMC, then it got worse!
(11a) Adjust your throttle linkage to insure that you also get WOT
from your accelerator pedal. I had to also do this.
(12) Tighten up the TPS bolts, verify the voltages are still within
range and put everything back together.
Drive the car a little, then readjust your idle air bleed screw if
needed.
Chuck Westbrook
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