Corsa-B.uk - Vauxhall, Opel and Holden Corsa B Owners Club

I need some support, please. The engine warning light of my son's 1999 Corsa B 1.2 ecotec came on on the motorway. He had just bought it and we were driving home. It wouldn't rev properly and wouldn't go any faster than 55 mph in fifth gear. It was fine in city traffic, no warning light. We did notice a slight hesitation on accelleration when shifting gears. We got home fine after the AA guy we called pulled the MAF connector, the engine was seemingly running normal without the MAF connected. The engine light was now permanently on.
I decided to buy a diagnostic scantool to read the faultcodes. I re-attached the MAF connector and cleared the fault memory first. This is what the scan revealed:

Identifier: 0690

systemNameOrEngineType: X12XE
systemSupplierECUHardwareVersionNumber: 01
RepairShopCodeOrTesterSerialNumber: Not programmed
ProgrammingDate: 19990301
CalibrationDate: 300201

Total number of fault codes: 4

P0130 - O2 Sensor Circuit Voltage Low
(02) - Not present

P0403 - EGR Valve Open Circuit
(04) - Present

P0110 - Intake Air Temperature Voltage High
(01) - Not present

P0100 - Mass Air Flow Sensor Voltage Low
(02) - Not present

What exactly does this mean? I am puzzled by the "not present". Does that mean the sensor is not present or dead? How serious are these faults? I get the impression it's the sensors that are failing, not the engine itself

Thanks for the help!

The maf sensor is dead thats why the car drove better with it disconnected as that causes the ecu in to default settings,

The o2 sensor is the lambada but i wouldnt worry about it it as the dead maf will be throwing the readings off