TPS Adjustment, Aftermarket ECU

[strmrdr23]

Hi C4AG!

i've recently noticed my car is bucking/jerking at low speed/rpm on both accel and decel. after some initial research online, it seems like it might be TPS needs adjustment. adjusting TPS looks easy enough however, all the tutorials i've seen online seem to be for stock ECU and i have a 16V high-comp small port in my AE86 with an aftermarket (Link G4) ECU installed. i've never played around with the ECU settings (i had it installed and tuned by a local shop) but i'm willing to give it a try. my question is, should i be adjusting the TPS itself or is it something i do through the ECU now? should i just start with a new TPS?

Thanks in advance.

[totta crolla]

TPS adjustment should be done through the ecu. There will be tps max (full throttle) tps min (idle) setting.

[strmrdr23]

ok. good to know. and if this doesn't resolve the jerking issue, any idea what to check next?

[jondee86]

If you have a read of this...
http://www.matrixgarage.com/content/4age-tps-adjustment
... it will show you how the TPS works and tell you how it should be adjusted. The
important thing to note is that the VTA signal should have a nice smooth change
from low to high resistance when the throttle is opened. There should not be any
hesitations, steps, dropouts or spikes in the reading when checked with a multimeter.

Check that first, as the carbon tracks inside the TPS can wear out at the bottom end
of the range where the sweep arm spends most of its time. The IDL switch setting
is not critical in your application. As said above, the max and min throttle settings
will be done in the ECU software.

Cheers... jondee86

[strmrdr23]

If you have a read of this...
http://www.matrixgarage.com/content/4age-tps-adjustment
... it will show you how the TPS works and tell you how it should be adjusted. The
important thing to note is that the VTA signal should have a nice smooth change
from low to high resistance when the throttle is opened. There should not be any
hesitations, steps, dropouts or spikes in the reading when checked with a multimeter.

Check that first, as the carbon tracks inside the TPS can wear out at the bottom end
of the range where the sweep arm spends most of its time. The IDL switch setting
is not critical in your application. As said above, the max and min throttle settings
will be done in the ECU software.

Cheers... jondee86

Thanks for the link, jondee86! i did read through that (it's probably the first thing that comes up when you google) but i wasn't sure if those steps only applied to OEM ECU. i'm a serious noob when it comes to fiddlin' with this new aftermarket ECU. can you give me the child version of what you mean by "The important thing to note is that the VTA signal should have a nice smooth change from low to high resistance when the throttle is opened. There should not be any hesitations, steps, dropouts or spikes in the reading when checked with a multimeter."

[totta crolla]

Double post

[totta crolla]

Think of the VTA signal as like a rotary volume control. VTA is the signal sent back to the ecu as a voltage, usually 0v - 5v approx
Sound should go from silent (0v) to full volume (5v) smoothly as you turn the dial. Worn parts of the control would mean the sound (in this case the voltage VTA) would perhaps be silent (0v on multi meter), then go very loud (5v on MM) and then quiet (2v on MM) as you turn the dial.

[jondee86]

What he ^^^^ says. Pull the plug off the TPS and hook up your multimeter to
pins VTA and E2 on the TPS (you can identify them from the diagram). Set the
meter to read Ohms, and rotate the throttle by hand. An old school analog meter
makes it easier to check the sweep than a digital meter, but either will do.

Cheers... jondee86

[strmrdr23]

you guys are freakin' awesome! i think i saw my dad's old analog multimeter in his garage (also where i store my car for the winter). i'll peep this out next time i go over there. so if there's spikes as opposed to smooth transition, i need a new TPS? Thanks so much, guys. i appreciate the sharing of knowledge.

edit - i found in the archives TPS part #s:

85-86 GT-S: 89452-28010 (Replaced by 89452-28040, 89452-20060)
87 GT-S: 89452-20070

idk how valid these are still. lol.