Hi everyone,

I could need some help interpreting the following graph of my oxygen sensor.

Car is a 2009 Fiat Ford KA 1.2L 69 HP with 138.000 km on it. Lately the engine’s idle speed fluctuates between 800 RPM and 1500 RPM, no check engine light, though there is a P0171 (system running lean) trouble code saved in the ECU. I’ve already checked for air leaks on the intake side.



Does this idle speed pattern look right? From what I’ve read, the signal should move from 0.1 V (lean) to 0.9 V (rich). Not quite there but also not that bad either?!
How about the period time? Internet says usual frequencies range from 0.5 Hz to 3 Hz. In my case the response is much slower and there is this gap that occurs every 10 to 15 seconds or so.
If I unplug the oxygen sensor or the MAP sensor, the engine runs smoothly.

Thank you very much for your support. I appreciate any help.

Best regards
Samuel

Can't say for your graphs, my first thought was throttle pedal or throttle position sensors or Lambda.
Our 09 exhibits odd behaviour at times, when stationary typically when cold you can raise the engine speed from 800 to 1000 a fraction more throttle and the speed gradually rises to 3500 a fraction less and it drops to 1000 again immediately

Just chuck a new Lambda in and see what happens.

O2 looks ok-i does sound like a vacuum leak-the engine gets more air, the ecu gives more fuel (hence the revs) and then the ecu tries to get it back to standard settings-could be a hole in pipe/brake booster etc-needs smoke test ideally

What is the purpose of the small hose that goes from the air filter to, I guess, the intake manifold (can't really spot the other end)? Found out that it looks like this today. But it didn't show any reaction to brake cleaner. :bang:



Best regards
Samuel

SamMedEng said:

What is the purpose of the small hose that goes from the air filter to, I guess, the intake manifold (can't really spot the other end)? Found out that it looks like this today. But it didn't show any reaction to brake cleaner. :bang:

View attachment 208298

Best regards
Samuel

Click to expand...

It's s breather and is a common failure stuff usually comes out(going to filter) rather than leaking air in.

Hey guys. I changed the lamda sensor today. Unfortuantely it didn't solve the problem. Just for the protocol, here is a graph of a brand new sensor.



It doesn't look much different, maybe a tiny bit more regular. Old sensor was covered with soot. I expected that as the car burns some oil.

In the meantime I've also checked the vacuum hose from the intake manifold to the brake booster. There were no visible cracks. Also no reaction to brake cleaner. Are there any more vacuum hoses? I have a feeling that the idle speed sometimes changes when I release the brake pedal?

Best regards
Samuel

Hey Samuel, did yo get anywhere with this?

Hey there, car runs great again! I ended up replacing the MAP sensor, which solved the problem. I also changed the spark plugs and spark plug wires. The car starts much better overall and the radio reception improved as a positive side effect as well.

Best regards
Sam

Hi Sam,

Thanks for coming back, interesting you mention radio reception as it's not great in our Ka! Did you need any specialist tools to replace the MAP Sensor?

Hi,
yeah, the radio reception in the KA is the worst...

Regarding the MAP sensor, you don't need any specialized tools to change it. The sensor is located at the left-hand side of the intake manifold and is secured by a single Torx screw. It takes only two minutes from start to finish to replace it. I got a new sensor from Bosch. It cost me about 15€, shipping included.

Best regards
Sam