When you notice that your 'fender reaches 70, can you hear any change in engine note, or can you feel the engine vibrating more when you push the accelerator the last 1/4 of its travel? Is there excess smoke produced from the exhaust? If the ECU is responding to your throttle position and it is indeed giving the engine more fuel, you should notice one of the aforementioned characteristics. The first thing I would suggest is a good service. Replace your engine oil, fuel, air and oil filters; filling the fuel filter with injector cleaner before fitting. Turn the ignition on and quickly dab at the accelerator ten times until the fuel system begins self priming (you'll hear it whirring away). Take it for a good blast and observe the characteristics of the engine. If the service hasn't helped things along, you might want to take note of the exhaust in your wing mirror as you press the throttle right to the floor nearing 70mph. If you see black smoke, you might want to consider the air intake side of the engine. Check all hoses between the intake vent on the drivers side wing, to the boost pipe between the intercooler and the inlet manifold. Any internally collapsed or perished hoses anywhere along the air intake system will suck flat and prevent air from reaching the engine. The same applies to splits or loose jubilee clips on pipe work after the turbo, which will allow compressed air to escape to atmosphere. If there is white smoke or inconsistent puffs of smoke from the exhaust you should be looking along the fuel supply line. Air leaks, blocked fuel lines or a failing low pressure pump in the fuel tank are all be potential suspects.
A good TD5 should certainly achieve circa 85-90mph.
-Tom
