Volkswagen 1.6i Strange Problem - Fixed - ScannerDanner Forum

9 years 6 days ago - 8 years 7 months ago #5927 by Ash03 Volkswagen 1.6i strange problem - Fixed was created by Ash03 Hi guys. I have a problem with a customers car. Its a vw polo 1.6 8v. It has a Bosch Motronic MP9.0 ecu. It doesn't have much electronics seems to be a very simple system yet its confusing me. This car has a 8 pin TPS with a built in idle control stepper motor, 4 pin map sensor with a built in air temp sensor, 4 pin water temp sensor, 3 pin distributor and a 3 pin knock sensor. IT DOES NOT HAVE A CRANK AND CAM POSITION SENSOR. The car came in with a bearing knock, fluctuating idle and a bad over fueling issue. Before stripping the engine apart I scanned for dtcs and I found 2 Codes 1. Map sensor short to positive 2. Air intake temp sensor short to positive I cleared the codes. Overhauled the engine. Started the car up again with the same sensor and I got the same dtcs and symptoms (fluctuating idle and over fueling) So I unplugged the map sensor connector and did a few tests 1. Checked for 5v reference on the map and air temp wires - was good got 5.01v on both wires 2. Checked for ground - was good as well 3. Signal wire has 5v (i believe the voltage varies depending on sensor output) So basically the wiring is OK. I tested the sensor next. Sensors output value was the same irrespective on the vacuum applied to it (it also smells burnt) so I replaced the sensor with a new part. After fitting on the new map sensor the car is still behaving weirdly. The problem the car has now - it starts up and dies after a second. It cannot idle. It revs up as if starving for fuel and cannot rev unless the throttle is open wide (WOT) but it does not throw any dtcs. If the map sensor is unplugged, the car can start and idle the same as with the damaged sensor (fluctuating and over fueling) If the TPS is unplugged and map is plugged, the car will start rev up fine, no over fueling it just doesn't idle as the idle control is built into the TPS. So I decided to test the TPS and it also works 100% Now im starting to get worried as I don't know what's going on. I then decided to get an ecu pinout and test all wires from ecu plug to the specific component that's being fed by the ecu. All turned out 100% no open circuits or shorts in the wiring. The car has no vacuum leaks, the timing is 100%, has proper fuel pressure. Can somebody please help me any input will be greatly appreciated. Last edit: 8 years 7 months ago by Ash03.

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