Monkie

I was reading through the November issue of Hot Rod (the one with the yellow 91 RS on the cover) and I found a tech article about "Throttle Position Sensor Adjustment Is Crucial To TPI Performance". What Im wanting to know is can we do this to our MPFI systems? Here is a brief section of the article....

"1: Locate the assemble line diagnostic link (ALDL) connector which is under the dash and just to the right of the steering column on most models; it may have a small block cover over the terminals. blah blah.....
2: Move to the engine bay and disconnect the idle air control valve (IAC), which is located on the bottom side of the throttle body (the connection faces the passenger side of the car). Be sure to allow 30 seconds after the vehicle is placed in field service mode before disconnecting the IAC. blah blah.....
3: To set the minimum air rate, start the engine. (it may be difficult to start, and it may run roughly at that.) Setting the minimum air rate is similar to setting the idle with a carburetor - a set screw on the drive side of the throttle body serves as a throttle stop, though you may find it plugged by a small metal cap. Remove the cap with a small punch or awl so that you can use a Torx 20 bit to adjust the throttle. Check the spec for your car, and if the engine runs roughly at that speed, raise it just enough to obtain a steady idle. blah blah......
4: it basically just says Once you've set the idle, turn the engine off, have the key out of the ON position. Remove the jumper wires from the ALDL and reconnect the IAC. make up three jumper wires to connect the terminals of the TPS with the harness you just disconnected. Make sure A is connected to A, B to B, and so on. Leave bare spots on the jumper wires to access the voltage meter probes.
5: With the jumper wires in place, turn the ignition switch to the ON position and connect the leads of a voltometer to the wires jumping the A terminals and the B terminals; it doesn't matter which wire gets the positive lead, the reading will be the same. It should be 0.55 volts, with an allowance for 0.075 volts either way. If you get a 5.0 volt reading, one of the voltmeter probes is connected to the C terminal, which is a 5-volt reference wire.
6: If the reading is not within factory specs, loosen the two TPS mounting screws with a Torx 20 tool and a delicate touch. Very often, the original screws, which are aluminum, will currode in place and easily snap off when you attempt to loosen them. Once loose, rotate the TPS to obtain the proper voltage reading. After you've set and tightened the TPS, gradually open the throttle to WOT (engine not running) while watching the voltage. The reading should climb gradually, at a rate that coincides with that of the throttle opening. Any spikes up or down in voltage could indicate a bad TPS. Note this test is difficult to perform with a digital meter, and really requires an analog gauge to monitor the voltage sweep. Once everything is set, turn the key off, remove the jumper wires, and plug in the TPS connector. All that's left is a testdrive."

I know its long and all but can someone help me out on if we can do this or not????? THANKS!!!

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1992 Camaro RS 3.1L
T5 Manual 5 speed
Open Air Intake
Z-28 Exhaust
8.5mm MSD Ignition wires
TB Coolant bypass

Kills:

95 (****) Probe GT
94 Mustang GT
91 CRX (dont ask me why he raced me)
2nd Gen Z28 (350) haha to you V8 guys!
1992 RS 305 TBI (good race)
More to come

TomP

Yes, and no. At some point GM decided that some cars would get a self-resettable TPS that wouldn't knock out of adjustment. I believe these have different looking connecctors, though. I think the non-adjustable units have a round connector, whereas the adjustable ones have the flat, 3-in-a-row connector (like on the MAF or MAP sensors).

I think 90-92 3.1's had the non-adjustable type. My '86 is the adjustable one. I usually do that procedure once or twice a year- although I don't mess with my idle speed (throttle-stop). I see no reason to play with it; it was sealed off at the factory, and can't mis-adjust.

Anyway you'll need a digital multi-meter. You can tell if you have the non-adjustable one because there won't be any adjustment available on the screws. With mine, I loosen the Torx screws, and I can twist it (adjusting it) and tighten the screws back down.

Oh - hey - that HRM had pictures of the TPS in there! If yours doesn't look like it, forget it. Heh, I shoulda thought of that earlier before typing all this... oh well.

The specs are slightly different than what's listed for v8's. I think the specs for the 2.8 are 0.55v @ idle, +/- 0.10 volts.


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-Tom P (Hot rodded 1986 Firebird 2.8l) from http://www.f-body.net/mailbag/3rd/3rd_mailbag.html message boards
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3.1 firebird

yea Tom is right about the 3.1's beign non adjustable. However, I stsrted messing with my idle speed after I installed my cam to smooth out the idle. Then I wanted to adjust the TPS, but its wasnt adjustable and it needed to move because I had the idle different than factory, so I simply enlarged the holes on the TPS with a drill bit and adjusted it.