Throttle Position Sensor Adjustment Effects

[91M30]

As I noted earlier on this forum, my 91 M30 had harsh 1-2 shifts when cold and delayed 3-4 shifts unless I backed off slightly on the accelerator.

At the suggestions of another forum member, I tried readjusting the TPS. When I rotated it a little CCW from the factory setting, the 1-2 shift got much harsher and the 3-4 shift delayed to even higher rpms, i.e., much worse.

Then I rotated the TPS a little CW from the factory setting and the 1-2 shifts got smoother and the 3-4 shifts occured at lower rpms.......so I rotated it a little further CW and it now shifts reasonably well.....and the engine runs and performs as well as ever.

However, this new TPS adjustment that works much better for shifting gives voltage outputs from the TPS (at closed and wide open throttle) that are well out of the tolerance range specified in the service manual. Are there any negative effects to this out of tolerance setting (emissions, mileage, etc.) that are not obvious?

What, besides transmission shifting, does the TPS setting affect?

Do the results indicated above indicate that I need a new TPS?

Does anybody else out there have any more input on how to check a TPS?

Thanks.

[Q45tech]

How far out of spec [tps idle and WOT voltages are what].......0.4-0.5 to greater than 3.8 is probably ok.

[91M30]

How far out of spec [tps idle and WOT voltages are what].......0.4-0.5 to greater than 3.8 is probably ok.

As the TPS is currently adjusted, and with test probes in the contacts of the TPS connector under the hood, the output readings are O.15 volts closed throttle and about 2.0 volts WOT.

As I mentioned in my earlier post above, when I adjust the TPS for a closed throttle reading of 0.4-0.5 volts per the FSM, the 1-2 shift is very harsh and the 3-4 shift is very delayed.

I'm assuming that the readings I get at the TPS are going to be approximatley the same as I would see at the input to the Control Unit inside the car?

[texasoil]

could be you are using a cheap VOM. Unless it is a high internal resistance one (used to be called VTVM) you are drawing too much current through the meter compared to the rest of the circuit. The meter is in parallel with the TPS resistance and you can easily get a low reading.

[Q45tech]

The engine ecu needs at least 3.8 volts from TPS to know you want WOT acceleration program.

Misadjusting the engine to solve a transmission fault is not wise.

The tps tells transmission what load you want 8 different steps and the transmission tries to adjust shift pressure to match load........TRIES is the key word here.

[91M30]

could be you are using a cheap VOM. Unless it is a high internal resistance one (used to be called VTVM) you are drawing too much current through the meter compared to the rest of the circuit. The meter is in parallel with the TPS resistance and you can easily get a low reading.

I am using a VTVM (vacuum tube volt meter), so the readings should be accurate.

[91M30]

The engine ecu needs at least 3.8 volts from TPS to know you want WOT acceleration program.

As currently adjusted, it only goes up to 2.0 Volts at WOT. I haven't had the throttle wide open on the road, but it seems to run fine up to normal cruising speeds (75 mph).

Misadjusting the engine to solve a transmission fault is not wise.

I agree....I sure would feel better if it shifted properly when the TPS is set per the manual......but if this is a transmission problem, what component could it be?

The tps tells transmission what load you want 8 different steps and the transmission tries to adjust shift pressure to match load........TRIES is the key word here.

Funny thing is, at current TPS setting it shifts pretty much as expected and doesn't seem to have any serious problems. Is there any way to tell from these settings and symptoms what the problem component might be?