1992 940 throttle position sensor

Pyrinex · Post by **Pyrinex** » 22 Jan 2019, 15:39

Opened one up today. It's only 2 switches. I was expecting a variable resistor. How do they work? And how they 110 quid?

Post by **jimmy57** » 22 Jan 2019, 17:13

That fuel system only needs to know closed throttle and wide open throttle. That is what the two switches do. Something costs what you will pay. Are you sure it is bad? I think I have replaced one many years ago and it was for corroded terminals in the connector.

Pyrinex · Post by **Pyrinex** » 23 Jan 2019, 02:28

The car is misbehaving. At start from cold it revs straight up to 2000 revs and then drops too 800.
When I put my foot down on accelerator while driving, there's a major split second hesitation (only from accelerator pedal fully up position) and then it moves off fine but only when cold. When it's warm it doesn't seem to do it but it's a little bit jerky it's a manual box) and sometimes accelerates slightly on its own.

I've tested the air valve on workbench, it works, I've cleaned out flame arrestor/ crank breather, I've put new temp sensor in, and a second hand tps.
If I unplug the tpi, the revs don't drop from 2200 revs so I think the connector is making contact.
I opened up the old tps (in the pic) and seen theres nothing too it and both switches work on both tps's.
Plus it's going through loads of petrol.
I've only had the car 3 months, I didn't notice any of this on the test drive.
I'm losing my patience with it.
Rant over, sorry.

dm635 · Post by **dm635** » 23 Jan 2019, 09:23

Same as 80's BMW's. I don't think a bad TPS is going to cause the loads of extra fuel. Unless WOT (wide open throttle is stuck on. They're easy to check with a meter. Hold a probe to the center pin and then to each outside pin to check idle and WOT. The variable resistance TPS didn't come along till the 960.

Post by **jimmy57** » 23 Jan 2019, 12:06

Is that a Bosch fuel system with MAF sensor in air cleaner hose or does it only have the two wire air temp sensor plugged in there? The Siemens fuel system uses a MAP sensor mounted on firewall to the side and uses a hose to intake manifold. MAP sensor issues or oil in vac line to MAP can cause that system to run like CRAP. I'm not sure if Euro market models used that system much or at all. Turbo engine models area all BOSCH .

Pyrinex · Post by **Pyrinex** » 23 Jan 2019, 16:23

Jimmy it is the bosch with the maf in the air cleaner pipe. I just had to Google what a map sensor is and I'm sure it doesn't have that and it's not got a turbo.

93Regina · Post by **93Regina** » 23 Jan 2019, 22:33

Pyrinex wrote: ↑23 Jan 2019, 02:28new temp sensor in

OEM or Part # is ???

93Regina · Post by **93Regina** » 23 Jan 2019, 22:42

Pyrinex wrote: ↑23 Jan 2019, 02:282000 revs...second hesitation...little bit jerky...

Sucking air...vacuum line(s) leak...brake booster shot...intake manifold gasket shot...o-rings shot

Throttle plate must be adjusted to OEM specs...no iffs, ands, or buts...

Post by **jimmy57** » 24 Jan 2019, 07:44

The temp sensor could be the problem. The sensor to be used on that car should be two temp sensors built into one. The two different types look alike and have the same electrical plug. The one you should use will have the same reading within a few Ohms if you read between either pin and the brass body of sensor (or engine when installed). The wrong one will be open between the pins and the sensor body as it contains only one thermistor and that one is isolated from the sensor metal body.
Earlier red motor Bosch EFI used a temp sensor but the Bosch EZK ignition module did not. As of 1989 both systems used coolant temp input. When the engine warms up the resistor in the wrong sensor would warm up enough for the interpreted signal to be maybe 100F and the idle would drop some. The ignition would get close to normal timing advance. When the load signal computation gets high enough the temp control is overridden so that would cause the delay then somewhat normal operation.
That sensor is not too hard to get to to measure resistance to get an answer.

markthomas1967 · Post by **markthomas1967** » 06 Aug 2020, 12:55

dm635 wrote: ↑23 Jan 2019, 09:23Same as 80's BMW's. I don't think a bad TPS is going to cause the loads of extra fuel. Unless WOT (wide open throttle is stuck on. They're easy to check with a meter. Hold a probe to the center pin and then to each outside pin to check idle and WOT. The variable resistance TPS didn't come along till the 960.

Could you say more about this test? I am placing red probe on center pin and black probe on left-hand outside pin facing outward (pics 1&2) and getting a reading of .000 ohms when valve is closed and a reading of OL when valve is open at all, but when I place the black probe on the right-hand outside pin facing outward (pics 3&4) I get OL when valve is closed and when valve is open at all? Is the sensor bad? Thanks.