My ford focus 1.8 turbo diesel (yr 2000) with intercooler suddenly slows down to idle speed. I cannot accelerate anymore. At the same moment the orange warning light ''preheating'' alluminates. When I switch the contact off and on I can accelerate again for a while. Can anybody help me with this?

check for hole in the intercooler and cooler seams
check for loose turbo hoses
check for seizes turbo actuator and control arm
check for failed hose to actuator

check for a blown turbo intercooler hose or split in the intercooler
have the fault codes read as it may not be the turbo at all

check if the fuel filter needs replacing

Sounds like a seal leaking in the turbo, does the car sit at more than 2000 RPM on the motorway?

Have a look at the intercooler pipes if the expand once you press accelerator if they do very little you need to check if there is no oil build up inside, if there is than you will have to get your intercooler and pipes cleaned or replaced.

I assume its the 6.0L diesel...If so sigh......double sigh.. I had one of these...triple sigh. I need a bit more clarification. How many km on the engine/vehicle. Also, you say that it blows black smoke while running at a constant speed at 2600 rpm, or while you are accelerating to 2600 rpm. Also, when you say the boost goes down, does it decrease by itself, or when the throttle is let off. The boost naturally goes down when the throttle is released (not trying to be a ****, i dont know how much you know). However, if the boost is going down by itself, while the engine is under load (its not supposed to, it should stay constant) it could be a couple of things, which "can" contribute to black smoke. If there is a leak anywhere from the turbo to the intake of the engine, it will cause the engine to get less boost, which means less air into the cylinders, which means black smoke. Check all of the connectors/tubing coming from the turbo to the intercooler, and from the intercooler to the intake manifold and see if there are any problems. The more costly problems which results in boost going down, and black smoke, deals with a problem with the wastegate on the turbo (controls how much boost is produced, and when too much is being made, it will bleed off excess pressure). So if your wastegate is malfunctioning, your boost will go down and you will get black smoke cause the engine is not getting enough air. also, around 160km...80mi, the injectors "can" start to go on the 6.0L diesels....I would check the turbo for leaks, the tubing for leaks, and the intercooler for leaks (a big rock can punch a hole in radiators and intercoolers...intercooler will be in front of the radiator). I hope this helps

DOES THE ENGINE MIL WARNING LIGHT COME ON? WITH OUT MORE INFO YOU NEED TO CHECK MOTOR ON A CODE READER FOR STORED FAULTS, CHECK ALL AIR LINES TO EMMISION CONTROL, , SOUNDS LIKE YOU HAVE GONE INTO SAFE MODE, A SPLIT OR LEAKING PIPE ON THE INTERCOOLER IS A COMON FAULT ON THESE, IF YOU SWITCH ENGINE OF AND BACK ON QUICKLY WITH MOTOR RUNNING WITH OUT STALLING MOTOR AND IT CLEARS THEN IT IS PROBERLY THE SAFE MODE CUTING IN MEANING A FAULT HAS BEEN SEEN BY PCM

try changing the fuel filter also check fuel quality,water may be in fuel, is it turbo charged? IF SO check for leaking induction components

could have intercooler leak or have blown gasket in turbo air system these will both cause your problem

Check out the throttle sensor.If its ok then you have a injection pump problem.IF you cannot turrn the engine of when the car starts reving then its running on its own oil.