Bad coolant temp sensor

[Royalrauch]

Could a bad temp sensor cause my car to run like crap? I have a 92 325i and the temperature gauge doesn’t work and it has hesitation and sputters/pops out of the intake between 1-3k rpms. Above 3k it gets better but still has no power. It only does it randomly. Sometimes I can drive it for a day or two without it doing it

[ed323i]

The M50 has two separate sensors.. One for the instrument cluster temp gauge and one for the DME/ECU.. So, unless they both died at the same time, the temp gauge coolant temp sensor shouldn't have any effect on how the ECU calculates the fuel injection times. If the ECU coolant temp sensor would be bad, then it would definitely affect the combustion, because the ECU can't properly calculate the fuel enrichment because it gets wrong coolant temp values.. Making the mixture too rich or too lean..

I think you should look for vacuum leaks.. And you could connect a laptop with INPA software and read all error messages and all live sensor values.. A malfunctioning coolant sensor can be spotted easily that way.. You could also look at the MAF (mass air flow sensor). You can disconnect it and see if the car runs better without it. If so, then your MAF is probably dead or dirty..

Good luck!

[Royalrauch]

I have checked most of the connections and lines on the top, replaced a oring on the line that connects into the middle of the intake manifold.I have cleaned my maf, and when I unplug it seems to run about the same maybe a little better. I have a check engine light 85% of the time that it happens which is 1221. The line that connects to the valve cover seems to be sucking in some oil. Also I do hear a hissing noise at idle

[ed323i]

1221 means something is wrong with the oxygen sensor, or that the ECU needs to adjust the fuel mixture too much (out of normal range)..
https://www.pelicanparts.com/BMW/techarticles/JF-Tech/E30_E36_On_Board_Diagnostics%20.htm

You could just change the O2 sensor if it's old, but in a lot of cases the problem isn't caused by the O2 sensor itself and the error will return quickly..
So, it could also still be a vacuum leak, or fuel pressure problem, or the ECU coolant sensor giving wrong values or the air temp sensor.. MAF doesn't seem to cause it, because it doesn't really run any different.

Best would be to connect your BMW to an INPA equipped laptop and read the live values (fuel adaptation, oxygen sensor values, etc). And also check the stored fuel adaptation values. Then you know a lot more (rich or lean, is the oxygen sensor giving correct fluctuating signal, etc)..

Good luck!