grsilvia1

Hello everyone,

My question pertains to the TPS on my 1990 C2 Tiptronic. Is the WOT sensor built into the TPS? There is a microswitch in the TPS that, in it's current configuration, is engaged at idle. There is also a stand alone idle microswitch separate from the TPS. Could both of these microswitches provide some input for a proper idle? Is ther any troubleshooting I can do with the TPS?

The idle has been irregular (very low when coming to a stop, then recovers after a few seconds) for quite some time now and I've been using the huge amount of info here to systematically work my way through troubleshooting. So far, I've replaced a bad coil which has helped a great deal. Also, I'll be replacing the spark plugs (Bosch FR5DTC) along with a set of Magnecor wires (the current wires appear to be the originals).

Side note, the distributor belt is OK. I've removed and cleaned the MAF and ISV. No vacuum leaks that I could find.

Thank you in advance for any help,
Gary

Lorenfb

On the 964, the DME unit is only affected by the throttle valve switches as inputs
to pins 52 & 53, 52 being the idle switch & 53 being WOT.

On Tiptronic vehicles, a TPS unit and an idle switch is used with a WOT switch being integrated
into the TPS unit. Both the idle switch & the WOT switch function as on the non-Tiptonic vehicle
only affecting the DME unit. The actual TPS provides load info to the Tiptronic unit.

So, if you're having an idle problem, it's the idle switch which affects it & not the TPS.
The idle switch should not "open" until about a 3-5mm movement of the throttle linkage.
A dirty idle valve will affect idle undershoot & recovery. As noted on this forum, lightened
flywheels significantly affect idle undershoot. Unless your engine has been modified,
it doesn't have a MAF but only an AFM. You need to make sure that both ignition
units are working properly by disconnecting one at a time.

For additional info, check here ( www.systemsc.com/diagnostic.htm ).

grsilvia1

Loren,

Thank you for your reply.

I've tested both primary and secondary ignition systems and both function.

My confusion is with the TPS. The microswitch in the TPS is only activated at idle. If this switch is the WOT microswitch then maybe I have an incorrect part. The TPS can only be installed one way, with a little room for adjustment and it has been on the car since I bought it in 2001 (idle was good until recently).

Attached pics show TPS with the microswitch in question, labeled B3. One image is with the throttle at idle (microswitch engaged) the other is at WOT (no microswitch engagement).

If this is the WOT microswitch and it is only engaged at idle, should I disable it?

Gary

grsilvia1

I should have added, the top image is at idle and the bottom image is at WOT.

Gary

Lorenfb

You need to just test the switch functions at the DME connector, i.e. pins 52 & 53,
using an ohmmeter. This will "tell" the real story!

g-50cab

So on a tiptronic car - there is a provision for the WOT signal to be transmitted to the DME - it's just not switch activated as it is on a non-tip car?

Bud Taylor

I figured out that by holdin my microswitch closed the car idled perfectly had a knowledgable mechanic adjust the cable and it idles perfectly (with lw flywheel)

HiWind

is this black plug the TPS plug? has 3 pins inside and is just below the ISV. Thanks!
ps - is the throttle microswitch (mentioned above) the black rectangular plastic piece that holds the end of the
engine end of throttle cable? Just trying to work out what is missing/disconnected on my
modifiied 3.8L with fuel mgmt system whic is idling at 1.8k. ISV is now clean but didn't help.
Fuel Mgmt system has 7 wires - ie for the 6 injectors and the timing, everything else is on the Motronic.

NineMeister

Whoever installed your Diktator system removed the stock idle and WOT switches from the throttle body and fitted a variable resistor TPS unit, hence by inference the Motronic ECU will no longer have an input at 0% throttle which is required to instruct the ecu and enable the idle valve function. Check this with an eletrical meter as Loren explained above; if the idle signal is missing you could temporarily wire in a loop wire to simlate the switch and check the idle function of the Motronic ECU and idle valve, if that all works the answer is to work out a way of re-installing the idle switch in addition to the TPS.

HiWind

thanks Colin! Starting to make sense now. I also don't have an AFM - needed? APologies for another q
but I'll check as you suggest and then worry about that

stevepaa

I had similar issue and eventually moved the sweep arms out slightly to find new tracks. no issues now.

HiWind

^^Hey Steve - do you mean sweep arms in the TPS?

stevepaa

clarification, I moved the sweep arms in the air flow sensor box

HiWind

Right - there's a DIY on YouTube - but I don't even have one ATM

NineMeister

No, you do not need the AFM. The reason why you have a TPS fitted is because the Diktator box controls the fuel injectors using an Alpha-N table, Alpha being the Y-axix for throttle angle (0-100%) and N is engine rpm on the X-axis. I don't know the Diktator system at all, so unless you also have an air temperature (AT) and/or manifold absolute pressure (MAP) sensors wired in, one can only assume that the system does not run any form of compensation tables for air temperature or pressure. If so, it's not very big and it's definitely not very clever....