6 replies to this topic

[Dailydriver77]

Hey all,

 

I am currnetly getting my '95 SPI back to life after a 17 years sleep. I'm mostly done but have a real strange behaviour of the throttle position sensor (potentiometer)

With ignition on I get a very slow response in the throttle position signal (checked using 2 different tools, MEMSfcr and MEMS mapper). For example I open the throttle manually using the rod and the electrical signal is changing very slowly from an already a very odd 200 mV to about 2100 mV in a timespan of around 4 minutes(!) It seems to be stuck around that value then.

 

When I close the throttle again, the value decreases very slowly.

 

The result is a very unstable idle because the ECU is always reacting based on the wrong value.

When I check the resistance manually (even took the potentimeter off the throttle body) the response of the resistance is reacting directly to the throttle's movement.

I don't really have any idea what might cause this.

Has anyone seen this before? Any suggestions what I might be looking for?

 

Already apologize if there's a specific thread already - I've tried the search but couldn't find anything... 

 

Thanks!

TJ

Edited by Dailydriver77, 13 November 2025 - 06:21 AM.

[NLinPEN]

You mention that you have monitored the potentiometer voltage via the scanning tools (MEMSfcr etc). Have you tried to measure the voltage directly? I haven't done so myself, so I don't know whether it is possible to connect a probe to the potentiometer directly.

[Dailydriver77]

That’s a great idea. Thought about it for a second but didn’t dare piercing any wires. But maybe I’ll make an adapter to do so…

[genpop]

Hello Daiilydriver,

could you publish a log from mems mapper as well as from memsfcr.On a short glance to your log on the german forum,there is a mismatch between Throttle position and poti voltage.

[68+86auto]

Here are the details for testing the sensor.

 

 1.JPG   32.5K   1 downloads

 2.JPG   20.74K   1 downloads

 3.JPG   52.58K   1 downloads

 

[Dailydriver77]

Thanks for your responses so far. I've had a rough patch lately so I haven't been near my Mini way too long  .

I hope I'll be able to test this next weekend.

@68+86Auto: I have a '95 SPI - that's only one ECU connector. But I have the pinout. Thanks again! 

[Dailydriver77]

I was finally able to check things again and I'm close to being sure that the ECU / the IC reading the throttle signal is the issue.

So I've made an adapter that let's me measure the acutal voltages and compare live to what MEMSfcr and MEMSmapper are seeing. Also made measurements with both.

Seems like no matter what I do to the throttle, the input voltage in my tools display around 0.3 - 0.5 V slowly rising. At the same time the actual output voltage is following what I'm doing to the throttle blade (in both measurements, I start with a closed throttle, opening it up completely, holding for 10-20 seconds and closing it again). Meaning, the actual voltage shows between 0.68 and 3.77 V on my voltmeter during that procedure.

 

To make sure all wiring is good I checked all pins at the ECU connector to the pins at the sensor connector. All show 0 Ohms, so good signal.

 

Any reccomendation to fix this? I'll open the ECU and check what IC is affected and see if I can have this fixed.

(by the way the intake air signal seems to be broken as well. I've checked all wiring here as well and even bought a new sensor, but constantly get a sensor error which leads to a replacement value of 35°C).

Anybody knows if that is read in the same IC?

 

Just in case anyone still wants to look into the measurements I was finally able to attach a zip file.

 

Thanks

TJ

Attached Files

•  MEMS_Measurements.zip   7.56K   5 downloads

Edited by Dailydriver77, 07 December 2025 - 03:51 PM.