Ursprünglicher Beitrag von: Martin Irving ,
Never trust any garage, after many years and many times of fixing peoples cars after garages have quoted exorbitant quotes for unnecessary work please take it from me as a qualified engineer in several disciplines that i hear that people trust their garages all the time. They want you to trust them, they need your custom. Ok… that being said try this first (it is the most common problem i have seen) and many people have returned from garages absolutely panicking about the quote given only to ask me. Pull off the plug from your airflow sensor (airflow sensors sometimes do not show up on diagnostic for a variety of reasons i shall not bore you with) this action will tell the ECU the sensor has completely failed and will put the ECU into a backup mode and the engine may run normally. Some cheapskates leave it disconnected which causes no harm but will have an affect on fuel consumption. Failing this i am unsure your car has a stepper motor for throttle control, but if it has it is worth swapping it… but before you do so all older engine management systems have a factory reset function, this is because the ECU learns someones driving style over a period of roughly 100 miles. If you are lucky you may find this reset procedure, being an older car, and this may help. It usually consists of something along the lines of turning your ignition on and off say three times, then in the on position pull off the fuel delivery wires, stepping on your accelerator pedal perhaps 6 times, then reconnecting the wire. Procedures are different for different cars but this will factory reset the ECU, clearing out any bugs. If your car runs roughly take it for a spin and it will settle down. However something tells me it may be this… Computerised cars are designed to cut petrol off from the engine at above the range your having your problem with when your foot is off the accelerator and the engine is running above roughly 1800 to 2200 rpm, it then cuts back in when it reaches the above range of revs to prevent stalling. This feature is to save petrol. Older cars usually have a switch, either on the accelerator like a brake light or at the end of the accelerator line (sometimes its just a microswitch) This can cause a cascade where your ECU tries to compensate. So it could be as simple as a sticking microswitch, Hence the intermittent nature of your problem. I can only offer these ideas without looking at your car, and remember, diagnostics don’t tell you everything, perhaps you have heard of planned obsolescence. Anyway good luck.