348 throttle position sensor adjustment

Time for another Stooge DIY.

First of all I would like to say thanks to whyte for giving me the specs for the throttle positions sensor resistance. I wanted to make sure both tps' where reading about the same numbers. The specs for the tps I got from whyte are:

1k Ω ohms at rest
2.5k-2.8k Ω ohms at wide open throttle

At initial start up the Motronic ecu uses the initial readings it gets from the tps for calibrating the mapping. After it's calibrated the resting position, the Motronic bases wide open throttle on the initial reading plus anything over 72º. As far as I can figure this is why when the car is learning/re-learing the initial warm up parameters (after power has been cut to the ecu/s) why you should not touch anything for at least 10 minutes. The Motronic needs this time to learn all the values, and if you do something to changes those values it can cause the Motronic to set the parameters = an engine that doesn't run properly.

So..................

I decided to see where my tps' were set, and adjust them as needed.

 

When testing the tps I needed to test on different pins depending on what bank of cylinders I was on.

Looking in from the rear of the engine bay,
On the right side of the engine (bank 1-4) pins 2 & 3 get tested.
On the left side of the engine (bank 5-8) pins 1 & 2 get tested

You can also see in these pics my tps' are Bosch part number 0280122004.
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When taking the readings for the tps at rest/closed I set the multimeter to 2k Ω.

My initial reading on the 5-8 bank, with the throttle closed, was 1.070Ω. In the ballpark but a little high for my liking. So I decided to adjust it to lower the resistance a tad closer to 1Ω even.
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I loosened the two screws holding the tps to the throttle body, gave the sensor a twist, then retested the resistance. That only moved the restitnace down to 1.055Ω. You can only twist so far because the retaining screws are in the way.
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So I decided to remove the sensor so I could get to the screws under it, holding the mounting bracket to the throttle body.

With the tps screws removed I used a standard screw driver to pop the sensor off the mounting bracket.
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With the sensor out of the way I now had access to the bract screws. I loosened both screws, gave the bracket a twist, tightened down the screws, put the tps back on (with a twist) then took the resistance readings. With this adjustment I was able to get the resistance down to 1.034Ω. Better, but I wanted it as close to 1.000 as I could get.

I can't twist the bracket or the sensor anymore so now what?
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Looking in the screw hole on the sensor I could see there was a little bit of plastic inside I could remove. This would give me a bit more wiggle room for the screws if I removed some of it. So I got out my file and removed some material. Put the sensor back on and tested. File a little, test, file a little more, test, file, test, file test until I had the restance reading at 1.002Ω.
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Even though I got the resistance of the throttle position sensor down to 1.002Ω when closed I hadn't taken the wide open throttle readings at the same time.

D'OH!!!

I took the WOT reading and it was 2.48Ω, under the 2.5Ω spec. I made some small adjustments and tested again. Oh, when I took the resistance I set the multimeter to 20kΩ. Adjusted the sensor until I had it at 2.55Ω at WOT and around 1.04Ω closed, then made sure I had the other side adjusted to match.
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There you have it kids, how I adjusted the throttle positions sensors on my 348, Stooge Style.

Happy wrenching.

 

Not really.
I wasn't having any problems per say, I just did it because I wanted both sides as balanced as possible. Sort of a "preventive" measure. However, whyte was having issues with how his car was idling. He adjusted his and did notice an improvement.

 

Nice!

Glad it helped

As for the seats swapping sides, I don't think so because of how the buckles are attached to the seats.

 

Thanks Randy.

 

Try swapping them from side to side.

You may also want to remove the idle air control valves and clean them out with some throttle body spray cleaner. Also check to make sure you don't have any vacuum leaks in the intake. Make sure that the vacuum tubes are in good shape and connected properly, that the hoses from the IACV are attached securely and aren't cracked, also check to make sure the nuts holding down the plenum to the runners are nice and snug, the same goes for the bolts holding the intake manifold to the heads.

 

The way I adjusted my idle was,

After the car had fully warmed up, and after I had taken it on a short drive, I unplugged the connectors from the Idle Air Control Valves/Extra Air Valves (as Ferrari calls them). I then screwed both air bypass screws all the way IN, and watched the tachometer to make sure the rpm didn't drop below 800rpm. Then a 1/4 turn at a time I unscrewed each bypass screw, on the side of the TB, until I had the rpm between 950-1000rpm. Plugged the IACV/EAVs back in and went for another short drive. After the drive I made sure the idle settled down to where I set it.

That is my Stooge way of adjusting the idle.

The proper process is explained in the shop manual, which I don't have in front of me. Something to the tune of using a manometer on both throttle bodies and balance the vacuum so it is even on both banks, then adjusting the idle speed. Again I don't have the manual in front of me so I can tell you exactly how they want it done.

 

Thanks for the update, and I'm glad it's working.