I am switching throttle bodies on my TPI motor. Is there a standard way for mounting and testing the throttle position sensor? Thanks

A voltmeter would be handy.

When you moount the new TB you'll want to get a rough voltage of .54v+ on the blue wire.

After that you'll need to set the minimum idle (described in the Tech Articles section of the frontpage to this site). My BBK came set fully shut which killed the car as soon as I bolted it on,,, don't be alarmed. Just adjust the throttle blades open more & then adjust accordingly to the Tech Article

It's not that hard but,, if you've got questions,, that's why we're all here,, to help out to the best of our knowledge/experience.

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Actually, the throttle blades should be shut - or at least closed enough that the engine will not idle with the IAC motor parked (closed). The IAC should have complete control over the idle speed. The adjustible throttle plate stop should be set such that the blades don't rest on the ID of the barrels with the throttle plates closed.

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Tim

1992 Z28, 305 TPI 5 speed, 12.1 sec @ 114.7 mph

1984 Berlinetta 305 TPI Auto, 13.8 sec @ 99.7 mph

Thanks for the information. It's a bit clearer what I need to do.

I might have this wrong Tim but, I thought (at least 2 of the F.I. books say & what made my car idle worth anything) was setting a minimum idle speed (450rpm for TPI),, throttle blades open enough for the car to run w/o the IAC (forsay the IAC died in the closed position). From that min idle speed, the ECM controls the idle speed via the IAC. Is that wrong info ?

When I put my BBK on,, it (the throttle blades) would move w/o binding but the IAC couldn't compensate for the throttle blades being fully shut,, it would just start & die unless the gas pedal was pressed slightly.

If I've got the wrong idea/info, I'd like to know myself. If for anything,, I've got my car wrong,,, & I certainly don't want to tell others the wrong info as well.

[This message has been edited by deadbird (edited October 26, 2001).]

I'll have to take a look in the shop manual to verify GM's recommendation on adjusting the screw position.

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Tim

1992 Z28, 305 TPI 5 speed, 12.1 sec @ 114.7 mph

1984 Berlinetta 305 TPI Auto, 13.8 sec @ 99.7 mph

Hey Tim, this is a shortened version of what I have for adjusting min. air.

- key on, jump the A-B terminal of the ALCL & wait about 30 seconds.

- leave ignition on & unplug the IAC leaving it in the fully extended position.

- Start engine;it will be running at minimum air speed.

- If idle speed isn't correct (4oo rpm for TPI), adjust the throttle stop.

- Set TPS voltage at this time too (0.54±.08 volts)

Does that sound about right (compared to a GM manual) or is the book wrong ?

Couldn't find an adjustment procedure in the shop manual. What you have stated will work fine, in that the idea is to have the idle set far enough below the ECMs minimum idle set point with the IAC closed so that it does not have to bottom out to drop the idle to the ECMs set point. According to the shop manual, on a TPI system the IAC system has enough air flow capacity to set the idle up to 1500 rpm.

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Tim

1992 Z28, 305 TPI 5 speed, 12.1 sec @ 114.7 mph

1984 Berlinetta 305 TPI Auto, 13.8 sec @ 99.7 mph

Deadbird, looks like you are right - if the throttle stop set screw is adjusted such that the engine will not idle with the IAC motor closed, then the IAC can't provide enough air for a smooth idle, once it is reconnected.

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Tim

1992 Z28, 305 TPI 5 speed, 12.0 sec @ 114.8 mph

1984 Berlinetta 305 TPI Auto, 13.8 sec @ 99.7 mph

Hey Tim, thanks for checking it out & making sure the info was right.

Tim and deadbird:

Thanks for the info. Let me bring you up to date on where I'm at now. I managed to get the idle to perform beautifully but I kept getting a MAF 33 error. All the checking I did with the scanner came up with the classic, that is, I had greater than 45gm/sec, at less than 2000 rpm, with the throttle less than 25% (like 1.19V). I called TPIS thinking that they had not programmed the prom correctly for the ZZ4 and the 58mm TB. They stated that they had raised the MAF limits to 255 gm/sec.

What I did next was to raise the TPS to 1.2V, this got rid of the MAF33 code but my idle was at about 1500 in park and 1100 in drive. I gradually reduced the TPS voltage till I found that the error would reset with effort at 0.73V. At this point I set it at .8V. I haven't finished troubleshooting yet but for now I've closed down the TB butterfies and am now idling at about 700RPM but I have to open the throttle a bit to get the machine started. I'm going to play around a bit more but any additional advice you could give me in the meantime would be appreciated. I'll study what you've written so far.

The car runs great and when the idle at starting is fixed it will be ready for the next phase (suspension & brakes)

Thanks

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88 IROCZ28
ZZ4, Big Mouth, Lg. runners and BBK 58mm TB. 700R4 w/ corvette shift servos, 3.23 Borg Warner & posi.
B&M 2400 Hole Shot and MegaShifter. Random Tech Hi Flow Cat and 3" Catback system, Edlebrock headers - jet coated.

Deadbird...with regard to TPS voltage readings...I've been getting code 22 low voltage reading...following the directions to the letter in the tech guide for setting the TPS...when I put the meter across the A-B terminals, my voltage readings are at .03 and with WOT I can't get more then 1.92 volts. Any guess why the voltage isn't anywhere where it should be...I can't set it like this?

i have a Code 22: Throttle Position Sensor/TPS voltage low what could be causing it to come back?