Should you leave the car engine in idle for a while before turning it off after a long drive?
Its true for a turbocharged vehicle , because most diesel turbocharged vehicles use oil for cooling as well as lubrication.A turbo charger spins at very higher RPM 1,00,000 ( still greater in certain applications ) and the temperature will be greater than 800 Celsius. The bearing is mostly a sleeve type bearing which is hydrodynamic type. Since it is a hydrodynamic , oil pressure ( 3–4 bars ) is required to keep two metal from touching each there.So if there is no oil pressure ( engine switched off ) there will be metal contact.Key pointAfter a cruising journey in a high way or streets , we used to park the car in a restaurant or house and leave the car without giving some time for turbo to settle.The turbocharger will be exposed to a lot of heat while the vehicle was running , which is cooled contiously by oil. If the car is switched off suddenly, the oil film between the bearings gets superheated and loses its lubricating capactiy. So a lot of residual heat is still present in the bearings which reduces the life of turbocharger.As others have pointed the turbo ( diesels ) wont be cooled by oil as engine oil cools the turbo ( engine is shut down ). This kind of temperature difference between turbocharger and ambient results in rapid cooling this can result in cracked turbo housings.What to do then ?If the stopping point is drive the vehicle at less RPM cause this will reduce the Turbo spools RPM or idle the car some time , you can spend this time checking tires , cleaning the seats , floor mats etc.Dont raise RPM like what lorry drivers do while shutting off their truck cause you accelerate the turbos again.Petrol powered carsTurbocharged petrol car use water to cool the turbo . they share cooling circuit with engine . Thermostat control this cooling circuit so cooling isn't a concern. But still oil is needed for lubrication may be the idling time for petrol car can be less .Check owners manual for the idling time , its pointed out in all owners manual , if isn't mentioned the car might be equipped with enough technology to prevent bearing failure or its might be water cooled even in certain diesels.
What are the symptoms of a bad transmission speed sensor?
On some vehicles, there are sensors that function specifically for certain parts of the vehicle. Sometimes a bad speed sensor will mess up the function of the ABS brakes (causing them to overreact or not kick in at all, which usually creates a light on the dash), other times it can cause erratic speedometer readings and/or (for auto transmissions) cause inconsistent shifts and it shifting completely out of gear into neutral at random. Some vehicles it will do all of these things at once, but you should get a CEL (check engine light) or ABS light to show up on the dash if one of these things are becoming problematic enough to cause issues.