Temp sensor causing rough idle?

[e30davie]

Its just a thermister.....there are ohm vs temperature values in the bently manual. check it with multi meter. if it works as it should then they arent broken. key thing is making sure the contacts are clean in both the temp sensor AND the loom plug.

[ScottySbk]

I can't explain how it works, but I just replaced my temp sensors a few weeks ago. Its super simple and they are pretty inexpensive. If they are old it might be worth replacing regardless.

yeah i’m gonna replace them anyways but i was gonna check it with a multimeter to see if it’s 100% possibly the problem but could i also unplug it and see how it runs or could it not run without it ?

[Lippy]

having a rough idle/power loss on startup but once it’s warmed up it’ll idle and drive great. I’ve tried everything else and led myself here. Temp sensor would could cause this right? it’s more so like im not getting the right amount of fuel when cold so i know the temp sensor controls the injectors and ratios and such just up until the o2 sensor warms up then that takes over right ? anyone wanna help explain ?

I can't explain how it works, but I just replaced my temp sensors a few weeks ago. Its super simple and they are pretty inexpensive. If they are old it might be worth replacing regardless.

[ScottySbk]

having a rough idle/power loss on startup but once it’s warmed up it’ll idle and drive great. I’ve tried everything else and led myself here. Temp sensor would could cause this right? it’s more so like im not getting the right amount of fuel when cold so i know the temp sensor controls the injectors and ratios and such just up until the o2 sensor warms up then that takes over right ? anyone wanna help explain ?

[mpowerful]

Thanks for the tip on ohming the sensor out. We will do it at sensor and at dme to check that circuit is reading true. Does bentley list the correct values we should be looking for?

[iliad]

It runs rough, my problem is not the coolant temp sensor...i tested it. It may be the wiring to the dme, u can test the ohms at the dme. I have ordered a ground strap from the oil pan to the frame rail, for my oil sensor light on the system board came on with oil at correct level.

For you i would buy the temp sensor, it cost like 20 from bav auto then go from there. The fact that it runs okay unplugged, to me shows that it give the wrong ohm level to the dme when cold. But that would be easy to test with meter

I've already replaced the temp sensor with a brand new one (twice) same result.

With the sensor plugged in it runs rough at cold start then clears up after its warmed up.

With the sensor unplugged it runs great all the time...

[comitsol]

It runs rough, my problem is not the coolant temp sensor...i tested it. It may be the wiring to the dme, u can test the ohms at the dme. I have ordered a ground strap from the oil pan to the frame rail, for my oil sensor light on the system board came on with oil at correct level.

For you i would buy the temp sensor, it cost like 20 from bav auto then go from there. The fact that it runs okay unplugged, to me shows that it give the wrong ohm level to the dme when cold. But that would be easy to test with meter

[iliad]

Comitsol.

When you unplug your coolant temp sensor does it run fine or no change? (Cold start)

[comitsol]

You can test the ohms for the sensor at various stages of temp. That is how the dme reads the temp. The ohm ranges can be found of online.

I am current going through this same issue.

My coolant temp sensor is good but still throws a code.

[mpowerful]

Trippman: that is the working hypothesis but why?

Digger: yes it seems to be the right one. Been through 3 now. Same issue.

[digger]

you got the right sensor?

[trippmann]

temp sensor is used by the computer to regulate fuel/air mixture during start up. so yes, if the sensor is bad it could possibly be telling the computer that the car is cold, causing it to run rich, which "once at operating temp" would cause it to have a rough idle.

[mpowerful]

Well thia car ran ok mostly until we got a cold snap. It was intermittent surging and idle issues. Replaced all gaskets because of potential mani gasket leak. Still with everything replaced it cold idle is doodoo. Pull the wire for collant sensor and it runs perfect. Everything....literlly everything has been swapped.

[superleggera]

I'm interested as well because I replaced my temp sensor too yet the problem still remains

[mpowerful]

1990 325is. This car has been completely refreshed basically. Timing belt. Cooling system. New harness. New cps. New 02. New intake gaskets and bitch tube o-rings. New exhaust mani gaskets. New valvle cover gasket. This car started out boosted and ran crappy until this maintenance was done. Car still has a rough idle during warmup. Unplug the brand new injector coopant sensor and it idles fine and runs fine. Exhanged the sensor for a new one. Same thing. Car runs fine without it plugged it but with it in runs crappy until warmed up. Tried changing injector harness too. Same thing. What gives?