TPS operation

[98SF19]

I'm a newb when it comes to ecu operation. I suspected my TPS was on the way out (per recent post on surging motor in park and idle) so I removed it and tried to clean it up a bit, along with the IAC but it didn't seem to help. Is it just a rotational spring inside the TPS? If so, I'm really surprised it lasted 18 years. I noticed that there wasn't enough return torsion in the rotating piece to bring it all the way back to throttle closed position. After reinstalling and restarting car, I actually got a code calling it out. Will replace soon, preferably using a speed perks reward PLUS a July 4th coupon code @ Advance. But here's my question:

If the TPS is telling ecu that the throttle is slightly open or more, does that increase motor speed by itself, even though MAF wouldn't be registering higher flow? I'm sure there is a full explanation of this on one of the 3 forums, but I'm too lazy to search right now.

 

[rubydist]

the pcm relies on the tps to a great extent under transient conditions - changes in throttle setting. the reason is that the mafs cannot respond quickly enough to change in airflow, so the pcm assumes airflow based on tps setting. that is why it is vital that the resistance slope of the tps is smooth and consistent. the return spring in the tps is not critical because the throttle plate has a large spring that will bring it back closed and force the tps with it, but the slope of the resistance change needs to be smooth.

the engine speed changes because of the airflow change, but the pcm needs to command more fuel to keep from leaning out, and that is where the tps becomes vital, so the pcm knows that the throttle has opened.

 

[98SF19]

Thanks for the info

the return spring in the tps is not critical because the throttle plate has a large spring that will bring it back closed and force the tps with it

My observation was that the tps spring is loaded as the tb plate is opened. IOW as the tb plate closes, the torsion of the tps spring unloads. This was based on the angle of the 2 tps "teeth" when I rotated it back to a stop (corresponding to tb closed position). So it seems my tps spring does not fully retract as the tb tab rotates back to closed position.

the engine speed changes because of the airflow change

Does this mean that my engine surging in park or neutral was not wholly related to bad tps? As you stated, the tb spring is strong, so it is returning to normal closed position.

 

[stephen newberg]

Your surging is much more likely to be due to the IAC. Sometimes cleaning them does not help, you just have to put in a new one.

pax, smn

 

[98SF19]

Thanks Stephen. Do the TPS code may have been due to my "cleaning" it?

 

[rubydist]

good chance the "cleaning" did not help and may have hurt the tps. they are not expensive, so good idea to just replace.

as mentioned above, the idle surge is much more likely due to a sticky iac. they are also not expensive, so just replace, don't even try to clean it.

 

[98SF19]

New TPS was the solution. $25 +/- after a speed perks and coupon code at AA, probably coulda got for less at Rockauto but didn't want to wait.
FWIW, I learned that when the motor speed jumped up to 2500+ rpms, to avoid slamming the car into gear to bring it back down, I was able to just unplug the IAC for a split second then replug. This brought the idle back down to normal without the impulse load. I'm sure there are fuses that could accomplish the same thing.

Drives fine now, shift points are back to normal. Still dealing with what feels like an occasional miss, but not enough to throw a code.

 

[Mikey]

Dirty post here... if you need to bring the idle down lightly tap the accelerator like 1% real fast repeatedly. ... makes the engine stutter. You didn't hear this from me, not great practice. Would love to know why it happens though.

 

[99sho-time]

the pcm relies on the tps to a great extent under transient conditions - changes in throttle setting. the reason is that the mafs cannot respond quickly enough to change in airflow, so the pcm assumes airflow based on tps setting. that is why it is vital that the resistance slope of the tps is smooth and consistent. the return spring in the tps is not critical because the throttle plate has a large spring that will bring it back closed and force the tps with it, but the slope of the resistance change needs to be smooth.

the engine speed changes because of the airflow change, but the pcm needs to command more fuel to keep from leaning out, and that is where the tps becomes vital, so the pcm knows that the throttle has opened.

Could you run us through what it takes to test the resistance slope of a tps? Could I just plug in my engine scanner with just ignition on and watch voltage? or maybe a job for a multi meter? I'm guessing it obviously entails moving the throttle.

 

[rubydist]

wow, life after death for this thread!

the way I look at the tps performance is a multimeter on the correct pins of the tps as the throttle is slowly opened and closed. you need to move the throttle more slowly than the meter responds, so for some cheap meters with lots of damping, that means really really slowly open the throttle. this is a project that takes 3 or 4 hands to do (or one foot in the car and 2 hands under the hood) so it takes an assistant.

 

[stephen newberg]

Sort of like the car, life after death.

pax, smn

 

[99sho-time]

Okay so I check my slope and it seems to have consistent linear voltage as a move the throttle.

The thing I notice with my car is the rpm's will drop while im holding the throttle.
Say im holding my throttle perfectly still at 2k rpm the rpm will drop by itself and lose power Im not sure I understand what this means.
I feel that should not happen.

sometimes my shifting is prfectly smooth and sometimes not..
Like today i turned around using reverse put it back in drive and the tranny clunked really hard as i went to take off.

it's also a new motorcraft tps sensor and I set to around .998 ish volts

 

[rubydist]

get the codes read and let us know what they are.

 

[99sho-time]

No codes so far. I have a scanner all the monitors passed except the evap. but im guessing its to early to tell.

 

[99sho-time]

I am really stumped on this one. my shifting doesnt seem to have anything to do with tps or iac.

I can't figure out why i have a hesitation in my motor if I blip the throttle your hear the rpm's dip to fast.

I check for vacuum leaks like crazy with starter fluid I couldn't find any. and I know my evap will prolly pass if enough time.

The maf in now is the right part number i picked up a cheap walker maf from rock auto when I put that one the fuel trims go crazy like -19.5%
And leans out the engine.

but my old maf seems to do the same thing just not as bad.

Its like the ecu cuts off fuel on then trys to add it or something.

Im so confused.

it has new o2 sensors, injectors , iac, coolant temp sensor coils and plugs.

one thing I noticed my tachometer acts jittery and strange sometimes sticking/

 

[stephen newberg]

It really sounds like fuel delivery. Have you checked on the output pressure from the fuel pump? Perhaps it is not consistent? Only thing I can think of considering your situation and what you have already done.

pax, smn

 

[99sho-time]

i checked pressure at the fuel rail and it seems to be normal. my fuel filter is new changed like a year ago.

The car seems to lack power in first gear but once it shifts it has alot of power. almost like missing low end torque. but tbh it feels like the tranny isnt engaging quick enough. im really not sure.

 

[Qshiplvr]

This may be way out in left field, but could the source of the problem be possibly further upstream, like the fuel filter?

 

[99sho-time]

This may be way out in left field, but could the source of the problem be possibly further upstream, like the fuel filter?

fuel filter is new.

Im starting to worry about compression. I know the headgasket is fine. unless its a small leak.

when i put car into flood mode. the starter turns evenly doesn't really sound like low compression. these cars seem to have strong starter it seems. so im not sure.

UPDATE: I just realize my scanner won't connect to the ABS. I replaced the module with a used one and i have no abs light so i assumed it was fine.

but im guessing if a scanner wont connect to the abs module , the abs module is bad?

 

[rubydist]

it depends, a lot of the scanners will not read the abs stuff, just the obd stuff.