3800 TPI, TPS sensor adjustment ?

[Paul Taylor]

Hi all,

Just a quick question that LMP can probably answer.

Yesterday i replaced my TPS sensor with a new aftermarket one. I got it from Ebay USA as it is impossible to get these kind of American car parts in the UK.
Anyway the origional GM sensor that i took off had 2 simple screw holes the same size as the Screws.

The new replacement TPS sensor had large elongated holes, which im assuming allow you to twist the TPS sensor to get the correct resistance reading in the Idle position ??.

I have checked my Pontiac Workshop manuals for TPS adjustment but nothing is mentioned, only removal and refitting.

I have a slightly high idle of 1100rpm now after my ECU has settled in after a day of driving. I am wondering now if it is because this new TPS is not quite the same as the stock GM item.

Thanks in advance.

Paul Taylor. UK
93 TS SE 3800 TPI
87 Camaro Z28 IROC-Z

[LMP]

THe book says the voltage from the TPS should be between "about" 0.5 V at minimum throttle position and "about" 4.4 v at maximum throttle. Read TP scaling. www.avigex.ca/xport/dtc21.jpg That should be easy to test and make any use of adjustments if judged necessary. BUt given the range of voltages accepted..specially at idle, I think the computer will adapt to the long term condition after more runs.

NOw the TPS function on this engine is not mainly to indicate the throttle opening, but its output is used to calculate at what RATE the throttle position changes. (that is what the book says...but I would have to read the lines of codes to see to what extent it does ONLY that). IN a way it is used to do what the old acceleration pump did in carburators.
That is why when it turns bad, that is, either loosing contact at some places or the track is cut so it jumps suddenly from minimum to maximum voltage or the contrart, both conditions are interpreted as very sudden throttle position changes, hence jerks and misses in engine output.

THen...if the idle speed is also modified by the TPS output it would tell that TPS is used at least in part to modify fuel delivery in relation to steady position...and we will rewrite the book...just for fun, I'd like to see what happens if the electrically connected TPS sensor is removed from car, engine running and one turns the TPS shaft.....ok it will eventually trig the CEL seeing a high TPS opening and no MAF related reading....but beside that...??