Function of TPS on 3.2 motronic

[curiousone940]

Could someone explain (in more than just general terms) the function of the throttle position switch on a 3.2 Motronic engine. What problems/symptoms are present when the TPS is either faulty or mal-adjusted?? Would like to either eliminate or pursue this component as a possible issue on my '89. Thanks for any input!!

[ML952]

The switch is for fuel-cut-off during coasting and for the enabling of the idle control valve function.

-> Possible Faults:

- Only little drag-torque, car is not really decelerating during lift-throttle
- No good idle rpms, changes in load are not controlled -> idle rpm drops when turning on electric devices (heatable back window, all lights,..)

Thats itm as far as I know.

Greetings,
Marco

[WydRyd]

My understanding of the TPS on the 3.2 Carrera is that it's NOT a variable potentiometer, like the later cars or 944's.

It's actually a 3 position microswitch, for Idle, Part Throttle and Full Throttle signalling to the DME.

Someone correct me if I'm wrong.

What are the symptoms on your '89?

[dwightp]

Which switch? There is a idle and full throttle switch. 2 seperate transducers.

I believe the idle switch is used for control of the idle control valve and decel fuel cutoff which is what Marco may be saying. If it fails, usually open, you may notice that your idle remains high (2k RPM or higher?)even after warmup.

The full throttle switch, is just that, "full throttle" signal to ECU. I'm pulling from memory here, but I vaguely remember it may operate open loop fuel delivery (ignoring O2 sensor and no feedback) and modify fuel and ign maps for best power and not for emissions and economy objectives. I believe it may also switch the a/c compressor off (if selected on) in some models. Never experienced a failure of that switch so perhaps someone with that experince can provide input.

HTH,

dwightp

[dwightp]

"It's actually a 3 position microswitch, for Idle, Part Throttle and Full Throttle signalling to the DME."

I believe you are correct that the switch may have more than one switch activating in it. However, I believe the harness and ECU is wired to only use the full throttle portion of this transducer. I'm not 100% on this though.

[Lorenfb]

"It's actually a 3 position microswitch, for Idle, Part Throttle and Full Throttle signalling to the DME."

1. Only two positions; idle and WOT, both are used (not a TPS which is a
variable resistor) used on later Porsche systems
2. has no affect on A/C
3. idle sw. - reduces injection time (basically zero) with RPM>1300 and Idle switch closed
4. WOT - increases injection time and ignores the O2 sensor

[curiousone940]

Gentlemen...I have posted an inquiry relative to "surging on acceleration" but I am still exploring possible causes. This subject seems to be a popular topic in this forum....infrequently, the culprit is very obvious, but more often, much time and $$$ are expended, without the benefit of a logical plan of action, before getting the desired result. My problem is an intermittent surging/bucking upon acceleration; air/engine temperature seems to make no difference. Car starts, idles fine....occasionally note some infrequent, mild surging at a constant throttle. New plugs, Magnecore wires, cap/rotor, CHT, O2 sensor, fuel filter. The intermittent nature of this problem leads me to believe there is a bad electrical connection that is impacting fuel and/or spark delivery, although I have not completely ruled out the possibility of a vacuum leak, defective fuel pump or fuel injector. Surely there must be a more "logical" plan of action to deal with these problems, rather than this "fishing" method, which of course explains my initial question relative to the TPS (which by the way your answers have now eliminated as a possible issue). Can someone help me "see the forest" here???

[Lorenfb]

Check out this web site (www.systemsc.com) on the Diagnostics page.
Your other solution is to take it to a Porsche repair shop!

[curiousone940]

For what it's worth, while attempting to address this surging/bucking issue earlier this week, I "jiggered" with the new Magnecore wires (just to make sure all was properly connected) and for the rest of that day, no surging/bucking problems. After driving the car 3-4 times, the surging/bucking problem re-appeared, so I concluded that the wire thing must have just been a fluke. Well, today I "jiggered" with the wires again and ergo, the surging/bucking problem has gone away. SO, before resorting to other, and perhaps more costly measures, I'm thinking I will replace the existing Magnecore boots with my old Beru boots and see if the fix will last more than a day or two. There are a couple of the Magnecore boots that just don't seem to have the right "feel and click" (you know the feel/click I'm talking about) when going on to the sparkplug. Has anyone else had this experience with Magnecore wires/boots or am I just imagining this situation...it seems to be for real!! Keeping my fingers crossed!!

[1968SWTs]

On the TPS, I believe canems.co.uk sells a "Bosch throttle potentiometer" as part of their TPS and ignition conversion kit

but IMO, MS is no better than stock unless you go sequential (add MS3x)

Clewett has nice stuff

1978-98 Cam sync adapter w/sensor [1001-61] - $190.00 : Clewett Engineering, The complete solution for ignition & fuel injection

[Tippy]

MS II is better than Motronic due to no barn door AFM and fully programmable ignition if you want.

I found it leaps and bounds better than Motronic.

Now, if you go Canems with all the bells and whistles (addition of TPS, MAP, etc.), then yes, the Motronic may be on par with MS.

[1968SWTs]

great video of Tippy's work

3.4 turbo 911 - YouTube

would love to see you take it to the next level





The Clewett TPS is $150 - Rothsport has something, and others have fabricated an adapter for a 993 or E30 TPS
http://www.clewett.com/index.php?main_page=product_info&cPath=5_31&products_id=75

[Chuck.H]

Off topic from where the OP is going, but... technically the system has 3 modes of operation.

There are two switches, one for idle and one for WOT. From a binary point of view, 2 bits equals 4 modes, but since one mode (both bits set high) is invalid, there are only 3:

01 = idle
00 = part throttle
10 = WOT
11 = invalid

Chuck.H
'89 TurboLookTarga, 347k miles