Alfa GT JTD Power Loss Traced to Manifold Sensor

Having some experience with these engines, I faced a very similar issue with my 2009 Alfa 159 1.9 JTD. The symptoms you describe match exactly what I encountered, poor engine performance, higher fuel consumption, and throttle response issues. Initial diagnosis suggested a MAP sensor problem, but when I took it to the workshop, they discovered a significant vacuum leak affecting the manifold pressure readings. The leak was causing incorrect pressure sensor readings, making the engine management system receive faulty data. The total repair cost was 235 Euro, which included diagnostics, parts, and labor. After fixing the vacuum leak, the engine performance returned to normal and fuel consumption improved significantly. Before jumping to conclusions about the MAP sensor itself, you might want to have the entire intake system checked for leaks. In many cases, the automotive sensor is working correctly, but external factors like vacuum leaks can cause similar symptoms. To provide more specific advice, could you share: Any specific error codes from the diagnostic? Have you noticed any unusual sounds from the engine bay? When did these symptoms first appear, gradually or suddenly? Has any recent maintenance been performed on the intake system? This information would help determine if your issue matches what I experienced with my vehicle.

Thanks for the feedback. I get DTC P0105 error code from my diagnostic tool. The symptoms appeared gradually over the last 2 weeks. I performed regular service at 91524 KM and everything was fine then. No strange sounds from the engine bay, just the poor engine performance and higher fuel consumption as mentioned. I checked for vacuum leaks but found nothing obvious. The intake manifold and surrounding connections appear intact. Based on the manifold sensor readings in my diagnostic tool, the values are inconsistent with normal operating parameters, strongly suggesting sensor failure rather than a vacuum issue.

Thanks for the additional details. Your case seems different from what I experienced with my Alfa 159. While my issue was caused by a vacuum leak, your diagnostic data pointing to inconsistent MAP sensor readings and the P0105 code directly indicate a faulty manifold sensor. The car sensors in these engines are quite sensitive, and after checking your mileage, it makes sense the MAP sensor might be failing. The gradual onset of symptoms and inconsistent readings are typical indicators of a degrading automotive sensor rather than a sudden vacuum leak. In my case, after fixing the vacuum leak, I still ended up replacing the MAP sensor a year later when it actually failed. The sensor replacement was straightforward and cost about 180 Euro including labor. The engine performance improvement was immediate after the new manifold sensor was installed. A few tips from my experience: Ensure the electrical connector is thoroughly cleaned before installing the new sensor, Double check the sensor is properly seated to prevent false readings, Clear the engine codes after replacement, Allow the engine management system to relearn for optimal performance Given your diagnostic results and the absence of vacuum leaks, replacing the MAP sensor should resolve your engine performance issues and bring fuel consumption back to normal levels.

Thanks for all the detailed insight. I will proceed with replacing the MAP sensor since all signs point to this being the culprit. The error code P0105 and inconsistent manifold pressure readings seem conclusive, especially with no vacuum leaks found. Your experience with sensor replacement is quite helpful. The 180 Euro cost seems reasonable and I appreciate the installation tips about cleaning connections and proper seating. Good to know the engine performance improvement was immediate after fixing your manifold sensor. Will get the parts ordered and have this sorted soon. The degraded engine performance and high fuel consumption have gone on long enough. Will report back once the repair is complete in case others face similar sensor failure issues in the future.