Neon MAP Sensor Issues Causing Major Power Loss

As an intermediate DIY mechanic, I had a very similar issue with a Shadow that showed identical symptoms. The pressure sensor readings were all over the place and the intake manifold was losing pressure due to a significant vacuum leak. After multiple attempts to diagnose, the workshop found cracks in the intake manifold gasket and deteriorated vacuum lines. The manifold sensor was actually fine, but was reporting incorrect readings due to the leak. They performed a smoke test which clearly revealed the leak points. The full repair included: Replacing all vacuum lines, New intake manifold gasket, Cleaning the MAP sensor, Computer reset Total cost was 235€ and it completely resolved the performance issues and check engine light. To better assist with your case, could you share: Engine size and year, Any recent repairs, Specific error codes from the check engine light, Whether you notice any unusual sounds or whistling, If performance issues are worse at idle or under load The symptoms you describe are classic signs of either a failing manifold sensor or vacuum leaks affecting sensor readings. A proper diagnosis with specialized equipment is essential since these issues can be tricky to pinpoint.

Thanks for the detailed feedback. My latest service was just 2 months ago at 112500 KM. The engine sensor readings from my diagnostic tool show P0105 which points to the MAP sensor circuit. Based on what you shared about the vacuum leak possibility, I will have them check both the manifold sensor and do a smoke test. The performance issues are definitely worse under load, especially when accelerating. The engine performance drops significantly when trying to pass other vehicles on highways.

Had the exact same P0105 code on my Shadow too. After my earlier repair experience, I can confirm that error code alone isnt enough to determine if the MAP sensor itself is bad. The automotive sensor might be reporting accurately but getting incorrect manifold pressure readings due to vacuum issues. Since your issues are worse under load, this strongly matches the vacuum leak pattern. Under acceleration, the intake manifold requires proper pressure regulation, and any leaks become more apparent. My engine performance was similarly affected during highway passing. Quick tip from my repair experience, have them verify the electrical connections to the MAP sensor first. Sometimes corrosion or loose wiring can trigger that code. In my case, the intake manifold gasket was the main culprit affecting engine performance, but I have seen cases where both issues exist simultaneously. The smoke test is definitely the right move. When they did mine, it immediately revealed the leak points that were causing the erratic sensor behavior. Just ensure they check all vacuum lines connected to the manifold pressure system, not just the main gasket. Would you mind sharing what the fuel consumption increase has been? Mine jumped about 20% before the repair.

Thanks, your experience with the smoke test results is really helpful. My fuel consumption has actually increased by about 25% compared to normal, jumping from 7.8 to nearly 10 liters per 100km. That matches what you saw with yours. I will have them do a complete check of the manifold sensor circuit and all vacuum lines. The performance loss during highway passing is getting dangerous, so I need to get this fixed ASAP. Based on your repair cost breakdown, I am budgeting around 300€ in case they find multiple issues like you did. Will update once the workshop completes their diagnosis. Really hoping its just vacuum lines and not a completely failed MAP sensor or damaged intake manifold. The fact that the problems get worse under load does seem to point toward vacuum leaks like in your case.