Throttle Position Sensor/Switch - Question about Part #'s

[prandelia]

Well, after bringing the new to me car home, filling it with some gas and taking it out for a couple drives to open it up, the car on a cold start the next morning really doesn't want to idle, is super rough, and dies on its own, or if I give it any throttle it will die also. If it can get warm through that phase it seems ok. I'm already literally hitting the reset button and going to replace all the sensors and typical items like spark plugs, coilpack, Tstat, water pump, 02 sensor, new rad cap, coolant temp sensor, upgraded timing chain tensioner, fuel damper, filter, and regulator, new EVO3 injectors, and throttle position sensor.

The one weird thing is the TPS on the car currently is part number 0280120319 not the correct 13621273277. I have no idea why this TPS is on their. My car is a 2.5L build, but I don't believe that has anything to do with it. Would this different TPS cause running/idling issues? I would assume so.

I get a little coolant pushing out the overflow tube when the level is correct and the car is just idling up to temp, but coolant reservoir doesn't seem to be pressurized the next morning after a drive (aka blown head gasket), as recent compression and leak down numbers are great. I know the symptoms sound like an intake leak or something along those lines, so will check all that too, but wanted to make sure this 319 TPS wasn't used for a specific reason that I'm not aware of. Going back to OEM TPS part, and probably going to just pay the high price for the Genuine BMW part, unless using the aftermarket 13621273277 parts is totally fine as well.

Thanks in advance for any input.

[HANDBLT]

https://www.mye28.com/viewtopic.php?t=119153

T

[prandelia]

Thanks. This has to be the issue. Ordered a new, correct TPS and will install it this week. Never ceases to amaze me how incompetent shops and owners are with their own cars.

[JimK]

FYI - 0280120319 is the Bosch number for the BMW part number 1362127327.

[prandelia]

FYI - 0280120319 is the Bosch number for the BMW part number 1362127327.

That seems incorrect. According to the post above and further investigation, Bosch 0280120301 = BMW 13621273277
The 319 is for M10, some M20, and some M30 engines. The 277/301 is specific for the S14 and S38 cars, along with some M20.

Confusing, but I'm sticking with the original BMW part number or it's most closely associated Bosch counterpart.

[prandelia]

OK, TPS has been replaced, along with new a new coil. Still have plugs/wires/ 02 sensors, etc. etc. and a crap-load of other little maintenance parts to install, but oddly enough when I unplug the "blue" coolant temp sensor on the motor (right side below plugs), the car will start right up, idle high at about 1k (like a cold start to heat up the cats) and let's me drive, but still cuts out and drives rough. Will continuously idle at 1k or so. So I replaced it with a new one. Same thing, unplug, and car idles high and rich. Plug in, car idles lump, and dies if you give it any gas.

Any indication on what this may point to as the culprit? Car goes into the shop on the 18th for a bunch of service anyway, and to diagnose this problem, but was hoping to figure it out before it goes in.

[Chris W]

Your car sounds like it's running rich, almost to the point of stalling out or not starting. I had the exact same behavior where the car wouldn't start unless I unplugged my coolant temperature sensor. In my case, it ended up being the barometric pressure sensor. Fixing it won't be as simple as ordering a new one. The new ones also come out of spec and will cause the car to run rich. Cracking open the sensor and adjusting it manually to the correct resistance is the best approach.

[HANDBLT]

Your car sounds like it's running rich, almost to the point of stalling out or not starting. I had the exact same behavior where the car wouldn't start unless I unplugged my coolant temperature sensor. In my case, it ended up being the barometric pressure sensor. Fixing it won't be as simple as ordering a new one. The new ones also come out of spec and will cause the car to run rich. Cracking open the sensor and adjusting it manually to the correct resistance is the best approach.

It will run fine without the bare sensor unplugged. Most actually keep it unplugged due to them going bad and creating a lean condition that will kill the engine.

Have you actually tested the TPS alignment and contact closures? It needs to be adjusted so that it 'clicks' audibly (and changes signal to the ECU) as soon as the throttle plates move. Then it will provide another contact closure signal around 80% (without a click) for WOT signal to the ECU.

It sounds like the wiring for the TPS is just giving the ECU an off idle signal all the time regardless of throttle position? What happens when you unplug the AFM?

T

[BBS16]

If the problem still exists after the above it could be worth checking the continuity with a multimeter from the coolant sensor, tps, baro sensor back to the ECU in case its all gone crispy and hanging on for dear life after all those years of under bonnet.

[HANDBLT]

If the problem still exists after the above it could be worth checking the continuity with a multimeter from the coolant sensor, tps, baro sensor back to the ECU in case its all gone crispy and hanging on for dear life after all those years of under bonnet.

this

T

[hardtailer]

https://www.r3vlimited.com/board/forum/e30-classified-forums/for-sale-wanted/parts-for-sale/214744-bosch-afm-refurbish-restoration-service-air-flow-meter-afm-s-for-sale

[hardtailer]

Your car sounds like it's running rich, almost to the point of stalling out or not starting. I had the exact same behavior where the car wouldn't start unless I unplugged my coolant temperature sensor. In my case, it ended up being the barometric pressure sensor. Fixing it won't be as simple as ordering a new one. The new ones also come out of spec and will cause the car to run rich. Cracking open the sensor and adjusting it manually to the correct resistance is the best approach.

Hmmm, some incorrect info here I'm sorry to say. Pulling above connector off the CTS equals very cold engine to the ECU which then enriches the mixture/increases fueling. If the engine then runs better, it indicates a lean mixture with the sensor connected. Idling at 1k rpm with the CTS disconnected is another indicator towards lean mixture as obviously there is enough air entering the intake at closed throttle to support 1k rpm as long as more fuel is added through the cold enrichment regimen.
The remark regarding what to do with the baro sensor reads like the hack for the AFM. inside the baro sensor is what you might recognize from a classic barometer/weather forecast gauge and not a wiper arm that you can bend to run at unworn part of the carbon resistive track like in an AFM (see earlier post). As such nothing you can adjust in the baro sensor.
Never heard that the are misadjusted from the get go either and I call heresy on that.

@OP, All those parts you want to replace do currently not cause what you're experiencing. Check your fuel pressure and spray pattern of the injectors
Look for false air entering the intake and as written above check alignment of TPS.


Start with the latter, good luck and report back please.

[hardtailer]

Spec on the baro sensor

http://web.archive.org/web/20051016044317/www.iigomotiv.com/barotech.aspx

[Chris W]

Sorry, but I stand by my original advice. I also have the specs from the iigomotiv webpage. When I couldn't get the car started, my barometric pressure sensor read 2.3k ohms. Given the altitude of my location the correct reading from iigomotiv's specs should be 2.5k ohms. I bought a brand new barometric pressure sensor from Pelican or Turner (I can't remember which now) and after installing it, there was no improvement in the car's running. It was also reading 2.3k ohms right after I received it.

It's not correct that the barometric pressure sensor can't be adjusted. If you take off the cover off, you'll see that large copper chamber that connects to a narrow arm that contacts the track. As the air pressure changes, the copper chamber will expand or contract slightly and it will move the arm to contact the track higher or lower along it. As the distance between the end of the electrode and where the arm contacts the track changes, the resistance in the circuit changes. I absolutely have taken a pair of pliers to bend the arm so it contacts the track higher or lower and have measured the changes in resistance as per the webpage. When I adjust it so it reads 2.5k ohms as the website indicates would be correct for my location, my car starts and runs perfectly every time. When it falls to 2.4k ohms, I can feel the slight drop in power, which is what I had years before when I dynoed my car and it was way too rich, down in the high 11s air/fuel ratio.

Unplugging the sensor may or may not help the problem. When the sensor is disconnected, the motronic will default to the sea level reading which will result in more fuel being injected to combine with the assumed greater air density. If the OP is in a high altitude location and the car is already too rich, disconnecting the sensor will only make the problem worse.

[hardtailer]

I stand corrected wrt the baro sensor. Thank you Chris for educating me on the inner workings of it and that it indeed can be adjusted/calibrated.

On the other hand I stand by my remark that disconnecting the blue CTS will richen the fuel mixture unless the sensor is internally shorted or reading far too low.
CTS is spec'ed as
at +20 +/- 1*C = 2.2...2.7k ohms
at +80 +/- 1*C = 0.3...0.36k ohms

As pulling the connector off you basically get infinite resistance the DME will increase fueling like it does with a cold engine.
Chris, how did you ascertain it was too rich as opposed to too lean with the CTS connected?
I would have understood too lean in case the CTS would have, say less than 400 ohms when trying to start a cold engine, as then disconnecting helps richen the mixture but from your description you didnt need to replace the CTS but only tweak the baro sensor. I'm miffed!


@OP sorry for taking this off-topic

[Chris W]

A few years after I bought the car, I went with some car club friends to a dyno day and had my car dynoed. I was curious about just how powerful the engine was as the previous owner had chipped it and installed the exhaust cam gear. When my graph came back the dyno operator mentioned that the car was a little down on power and showed me the air fuel ratio during the run. It started out in the mid to low 12s and then at high rpm went down to the high 11s. He told me that if I could lean out my fueling I could easily gain another 5 hp or more.

That started me down the road of chasing this problem, and it took me years of false leads and failed solutions. I started by ordering a remanufactured AFM. At first I thought it might have made a slight improvement in the car's feel, but looking back I think that might have been a placebo effect. I also heard that the CTS could be a problem, so I replace it even though the readings were reasonably close to what they should have been, and again not much improvement. I also read the common advice that when the barometric pressure sensor fails it makes the engine run lean, so I replaced it with a new one, and again there was no improvement.

Over the years, the car was start every spring, but it seemed like every year the first time I started the car after the winter seemed to get tougher and tougher before it would finally start. I also noticed the car would buck and stumble badly when the engine was cold whenever I tried to give the car any serious throttle, and I was only getting about 225 miles on a tank of gas. Once the engine was warm everything again seemed normal. That trend progressed year after year, until one year the car wouldn't start at all. At that point, I tied the trick of disconnecting the CTS, and sure enough it would start with it unplugged. If I plugged it back in when the engine was cold, the car would stall, but if I let the engine warm up before plugging the sensor back in, I could still drive the car. Eventually, even that trick no longer worked. That then led me to suspect the injectors were either leaking or stuck, so I tried sending them some place to be cleaned, and when that didn't seem to help, I replaced them with new ones, but the car still wouldn't start.

After all that I tried rechecking the things I tried to fix the car, and even replaced the CTS a second time. Eventually, I came across the information on this site with the correct values at various altitudes for the barometric pressure sensor. When I measured the sensor it came back at 2.1k ohms (not the 2.3k ohm I wrote above. At 2.3k ohms, the car would start, but have the bucking and stumbling problems), which would have indicated the car being over 1,000 ft lower in elevation that it actually was. Since air is denser the closer it is to sea level, I reasoned that the sensor was causing the car to run rich. That also got me thinking that disconnecting the CTS was able to make it start because it was leaning out the mixture just enough for the engine to start, at least for a few years. Maybe the Motronic has been programmed to interpret a disconnected sensor as a default temperature value such as normal operating temperature? I double checked the reading with my old sensor, which I kept as a spare since it didn't seem to be any more faulty than the new one I bought, and sure enough it also reading too low. That's when I took my original one apart and manually adjusted it to 2.5k ohms where it should be. The car's run flawlessly ever since, and now I usually get 275 miles on a full tank.

Every other year or so I start to notice the car being a little sluggish, and that's when I know I need to readjust the sensor again. Once's that's done, I can again feel that the car has that little extra power or snappiness to its throttle response.

[hardtailer]

Thanks for taking the time to respond so comprehensively!