TPS, IAC counts and MIN AIR

[CDeeZ]

Okay so I have been really busy with work, class, and other car projects so I have neglected to mess with tuning much here lately.

I just recently finished rebuilding the banjo axle in our '32 Ford, and I have also begun working on my pro street Nova again. The banjo axle has 400 miles on the new gearset so looks like my setup of the gears was good.

Anyways, with some of these things out of the way, I decided to hook up the laptop to the TBI and see how things were doing.

It seems that no matter what, if I set my MIN AIR RATE so that the IAC has LESS than 30 counts at idle, then for some reason, my TPS is hanging up at 0.4% instead of returning to zero. It seems like the throttle plates are binding up in the bores, and if I back the screw OUT, so that the IAC counts go up to around 30, then it seems that the TPS does NOT hang up and 0.4% but returns to zero like it's supposed to.

I'm at anywhere between 30-40 counts IAC at idle, fully warmed up engine, no other loads on engine..... This is a little higher than what most target when setting IAC counts at idle, but is this OK? Anything less for IAC counts seems to mean the throttle plates stick and the TPS sticks at 0.4%...

Can leave my IAC counts between 30-40 at idle since it seems to be the only place the TPS doesn't stick??? Also, could my TPS be bad??? How would I test one??

[EagleMark]

Just set it by IAC counts!

There is no TPS% in $42 The TPS% value in TunerPRo RT is a calculation from voltage and not a true TPS%... it's lieing to you... sorry...

[babywag]

I'm going to say the throttle shaft opening in the TBI is worn.
The throttle is not closing all the way due to the wear.

On my '90 my TPS reading was not returning to .5v aka 0%.
I noticed the throttle shaft was pretty sloppy, so I replaced it with another throttle body.
When I checked the replacement it was much tighter.
So I threw a rebuild kit @ it, and installed it...grrr same thing
Not as bad, but still annoying as hell.
The replacement throttle body shaft was tight on the driver's side, but loose on the passenger side and I never thought to check it.

If I ease off the gas I get 0.4%(aka .57v) reading in TunerPro
If I give it a quick stab it drops back to 0%(aka .54v)
If I abruptly let off the gas it returns to 0%(aka .54v)

My solution was to add a return spring, lame to have to but works.
I'm not going back in a 3rd time.

[CDeeZ]

Not running 7747-$42 anymore... Been running a 7427 PCM w/ $0D mask for probably a year now.


Yeah I have rebuilt my throttle body but it's been a few years. Maybe the TB itself needs rebushed?

My setup seems to run fine with 30ish IAC counts, and I haven't seen the TPS get stuck at 0.4% since I adjusted the min air rate screw the last time.

Greg posted this in a previous thread I had titled: "idle a little rough"

gregs78cam:
"EDIT: I just noticed your TPS is at 0.4% at the end of that log. It should read 0.00. Check that your throttle cable/blades/pedal are all free, and that the TPS always returns to 0. The '7427 has a section of code that "Auto Zeros" the TPS input. If it is not returning to 0.00 then it thinks you are still pressing the gas, even just a little makes a difference. "

[EagleMark]

After you turn min air screw in. Do you see the .04%? Turn the vehicle off for 10 seconds and restart, still there? If so something is sticking. The PCM will set TPS to 0% when started.

[RobertISaar]

i'm not 100% on the later TBI stuff, but if you change the throttle stop around in any earlier applications, reseting the NVRAM is necessary for the PCM to learn the new minimum TPS voltage for it's 0% auto-zeroing function. they don't lose that value upon key-off, it needs a power disconnect.

[CDeeZ]

The way I've been doing it is to turn the screw in a good amount, then back the screw out a little bit at a time until IAC counts fall in line. This way the threshold will not be surpassed by turning the screw too far inwards, thereby causing IAC to stop controlling idle.

I guess what I need to try next is unplugging the ECM as Robert is saying.


I start out driving/logging and the TPS is 0.0% for a while, then sticks at 0.4%...... I've even made a log of it alternating between 0.4% and 0.0%......
Hrmph

[CDeeZ]

My TPS is still intermittently hanging up at 0.4%. I have at least one other throttle body laying around, maybe I should swap it on to see if the issue goes away?

[EagleMark]

If your sure there is no cable hanging up or?

The min air screw does create an indentation on throttle stop, after years then tend to close a little. Then you tuned it so indentation does not line up? I wonder if a little file in there would smooth things out?

Something is causing a hang up and only if adjusted? I've done a lot of this and never had this issue? Maybe open throttle blades all the way and let them snap back shut a few times?

[babywag]

If your sure there is no cable hanging up or?

The min air screw does create an indentation on throttle stop, after years then tend to close a little. Then you tuned it so indentation does not line up? I wonder if a little file in there would smooth things out?

Something is causing a hang up and only if adjusted? I've done a lot of this and never had this issue? Maybe open throttle blades all the way and let them snap back shut a few times?

Like on my above post I'd still bet the throttle shaft has slop in it, this allows it to "close" in a different spot than 0%.
That's why when you start truck it's @ 0%, and sometimes it hangs @ 0.4%
On mine it's the passenger side throttle shaft opening that is worn, I can wiggle it and watch the % change.
On the previous throttle body the driver's side throttle opening was worn caused same issue but worse.

Finding a nice tight throttle body came up a bust for me. Most are 18+ years old now.
Several trips to the local yard, and every one of them was worn.

[EagleMark]

I'm not doubting you or the shaft is worn. Just never adjusted one and saw it end up with a variable TPS% at closed?

[RobertISaar]

i'm not so sure i would be worried about .4% being registered.... all of my vehicles have done that at times, but no ill effects.

[ony]

see if the voltage is changing with the % change, that amount of % change shouldn't change the volts.

[ony]

my tps % was going 0 to -1 49-51 volts , hooked every thing up ( pc, tuner pro ,engine not running ,key on) adjusted the throttle scrcew in an out pushed gas pedel easy- snaped it hard till it would stay the same mine is worn out but it is still usable like 85 % of the throttle bodys I have seen, my iac count runs 3-17 idels pretty good but it is a std trans.play with it a little you will get it right,if your tps is not adjustable drill the mounting screw holes out a little to give you a little adjustment.