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Corsa 1.3 CDTi Life 2004 - Corsa 1.3CDTI low power, EML/emission lights on - shauncwalsh

Hi
I have a 2004 Corsa 1.3 CDTI 75HP, 140000 miles, which has the following fault.
Engine management light came on, engine low on power and would not rev over 3250rpm.
Turned engine off and on again, engine management light went off and emission control light came on.
This happened a few times, sometimes power was not affected, sometimes it was, now emission conrtrol light on more or less permanently and engine will not go over 3250rpm.
Took it to garage who read off fault code (no they didn't tell me the number) and said it was a turbo fault, quoted £500 to change it.
They said that the vanes were probably sticking, however I have been under the car and looked at the turbo and it appears to have a waste gate not variable vanes (as you would expect with the 75hp engine). The waste gate actuator moves when levered with a screwdriver and the pressure pipe looks intact.
Am I right in thinking that the turbo boost pressure is measured by the MAP sensor?
My thinking was that if the turbo looks OK then the MAP sensor could be faulty, I took it off, cleaned it and replaced it and disconected the battery for half an hour to clear any faults. Reconnected battery and no faut, engine runs fine.
Next day fault is back, my thought is to replace the MAP sensor, any other suggestions?
Thanks.

Corsa 1.3 CDTi Life 2004 - Corsa 1.3CDTI low power, EML/emission lights on - Railroad.

I would start by thoroughly checking the air intake system for leaks and security. Also check the EGR system, and if possible using a lamp look inside the inlet manifold downstream of the EGR valve and check for the build up of thick sludge which would restrict air flow. If everything is OK the next stage will be to get it hooked up to a suitable diagnostic tool and take some live data. Also the fault code should give you an idea of where to start looking. Don't do what everyone does and take the fault code as gospel. For example if the code says Mas Air Flow Sensor don't automatically assume that the sensor if at fault. The ECU cannot distinguish between a low mass air flow fault because of a faulty sensor, or a low mass air flow fault because of low mass air flow. Don't be fooled. Do the checks.