STRETCHED Throttle Cable zip-tie fix barely changing TPS... sensor NOT easily removed.

[fixizin]

{I know the infamous throttle cable slack-over-time issue is not engine-specific, but didn't know where else to post it.}

BEFORE: Ancient OBD-II reader says idle position TPS reading is 14.9% (normal?), and mashed to the floor is only 87.0%... not good.

ANY-hoo, did NOT want to remove driver's seat, and finally figured out that 2 milk crates (and a couple layers of bubble-wrap for mah lower back over the door-sill) is the same height as my cab-floor, slid the seat all the way back, pulled the dome-light fuse (#26), and got after it... ended up getting 2 5mm ties and 2 3mm zips on there... that's a solid 5/8"!... and YET:

AFTER: Idle position TPS reading is still 14.9% (so I didn't OVER-do it), but WOT is increased to only 87.8%... WTF?

My 4WD XL-trim has the rubber flooring, but under that is a much thicker pre-formed layer of black rubber padding/soundproofing... seems to me this is preventing full pedal-travel... what say ye, RKIs???

PS: what "redline" (computer-limited) RPM should I see @ 100.0%/WOT??

 

[RonD]

Actually no, not the gas pedal end at all

TPS should be 19% to 90%, so adjust the TPS

TPS is a 5volt sensor, you should never see 0% or 100%

Just under 1volt throttle closed is spec, so just under 20% is expected, 1volt is 20% of 5volts, so 18 or 19% throttle closed
At wide open throttle 4.5volts is expected, 0.5v is 10% of 5volts so 90% or 92% is fine, never 100%
To the computer, under 20% is idle, foot off the gas pedal, 90% or higher is WOT, damn the MPG pump in the gas as fast as possible, lol

So you have the range, 15% to 89%, you just need to adjust TPS to add 3 or 4% to bottom end so its 3 or 4% higher at top end

In the good 'ol days TPS screw holes were slotted so you could adjust TPS, now a days especially 3rd party sensors don't have much adjustment, but you can try, loosen the 3 screws and turn it as far as you can, re-tighten and check %
You can pull the TPS and drill the 3 holes a little larger to get an adjustment

In 1999 there may also be an anti-diesel screw, looks like an idle screw, on throttle linkage
You shouldn't mess with this screw but can if you do it right
After engine is warmed up and idling, unplug the IAC Valve, idle should drop to 500 or so, engine barely running
If engine stalls then turn the anti-diesel screw a 1/2 turn clockwise(tighter) and restart engine, you want it to idle but under 650rpms with a manual trans, 700 with automatic
This adjustment will increase the idle % and so the WOT % as well, you don't need much

After adjustment plug back in IAC valve and idle should go back up to computers "target idle", 650-700 for manual, 750-800 for automatic

 

[fixizin]

No chance to test-drive until today, throttle definitely "comes alive" way earlier in the pedal-travel, yay for zip-tie horsepower, hope I don't get a calf-cramp from holding foot higher, lol...

PS: what "redline" (computer-limited) RPM should I see @ 91.0% TPS = WOT??

PPS: ... and will 90-92% TPS trigger the "WOT" diagnostic modes?... (from experience I know the 87.0% does NOT...)

 

[RonD]

4.5volts or 90% is WOT to computer

 

[Lefty]

Most of us have done that and been there, but maybe this photo of the zip tie fix might clarify for those who haven't.

 

[fixizin]

Yep, that's where I put my cable-ties, at the very top, 'tween the swaged-on stopper and the plastic spring-guide... can't wait to get under the hood (instead of the dash) this weekend and git me some WOT!

 

[fixizin]

Holy BLOCKED tool-path Batman! Ain't no gettin' to those 2 TPS screws, esp. the rear one... even if I remove the DPFE sensor, the intake manifold is in the way of even the stubbiest of screwdrivers...

... looks like the entire throttle-body has to come out?... and even then, it doesn't look like there's ANY adjustment/slotted-design to the 2 (not 3) mounting holes, nor does there appear to be enough "meat" there to enlarge the holes... can I shim it INternally? Or after all that disassembly hassle, will a NEW TPS do the trick?

What say ye, RKIs?

PS: while under the hood, verified that throttle cable IS rotating the throttle-plate all the way to the stop... wish I'd checked that before adding the zip-ties... oh well. (Yes, it does have the "anti-diesel" screw at the idle-end of travel...)

 

[Josh B]

Which one are you trying to get to? and have you seen the price of zip ties?!

 

[fixizin]

I marked the 2 screws in question... BUT basically it's a matter of I've picked up a few extra ohms in my wiring... a blast of contact-cleaner in the plug?... is there a trim-potentiometer near the ECU?...

 

[RonD]

Pull off the DPFE sensor and you can loosen the screws, see if there is movement in the right direction, i.e. key on check TPS %
see if you can get 90% WOT

 

[fixizin]

I'll have to find my super-stubby #2 Phillips, and the weird Craftsman slip-joint pliers w/ rubber "condoms" on the jaws to turn it... ... still rather just tweak a trim-pot, while eyeing my voltmeter...

 

[RonD]

Problem is..................your are voltage shy, only getting 4.3volts and need 4.5volts at WOT, so can't "trim" that with resistor

 

[fixizin]

I know, I'm saying IF THERE WAS a trim-pot inline with the signal wire, it would be spec'd to be mid-range when new, and thus you could either add or subtract resistance as components aged... instead of paying FoMoCo for a whole new NON-adjustable potentiometer called the TPS.

 

[fixizin]

If engine stalls then turn the anti-diesel screw a 1/2 turn clockwise(tighter) and restart engine, you want it to idle but under 650rpms with a manual trans, 700 with automatic
This adjustment will increase the idle % and so the WOT % as well, you don't need much

After adjustment plug back in IAC valve and idle should go back up to computers "target idle", 650-700 for manual, 750-800 for automatic

It's easy to see how that anti-diesel screw affects fine positioning of the idle/throttle-plate-almost-closed, but... I don't get how it increases travel and therefore TPS voltage at the WOT end??? I already stated that cable (via gas pedal) is rotating plate-arm all the way to the upper stop... ??

 

[SenorNoob]

It won't. Therein lies your problem. Question is, have you checked the 5v reference? Sounds like you have, but what is it? If you know that have a true 5v from the PCM but less at the TPS then the only real option is to fix the resistive wiring in between. I suppose a 5.1v source could be used to make up for the difference, but it'd always be a kludge. Albeit one that we use on million dollar machines at work with some regularity.