Why are modern cars so complicated?

My car (BMW 520d) got me to France and back without incident, another 1600 miles on the clock, but it has not been running right for about six months.

It’s in the garage now to try to sort out a problem where it will sometimes almost stall when pulling away or fail to pick up when you put your foot down.

It’s had new glow-plugs, the particulate filter checked and now may need a throttle position sensor or mass air-flow sensor replacing (we’re not sure which, both or neither).

Older cars were less reliable but more resilient – instead of a throttle position sensor, you’d have a cable connecting the pedal to the carburettor; now it’s a drive by wire connection to the fuel-injection system.

When something goes wrong, it’s a holy mess trying to find out the cause and, instead of a £15 throttle cable, it’s probably a £200 sensor.

I’m getting to the stage with this BMW that, if it’s not sorted out soon, I feel like just scrapping the bloody thing. This is its fifth day in the garage this year and it’s still there – six days tomorrow!

Update (20.2.14): Still not sorted, but four sensors on order - throttle position sensor, mass air sensor, engine temperature sensor and outside temperature sensor. They should be delivered tomorrow or Saturday and the car is back in next Tuesday to have them fitted.

Update 2 (6.3.14): Hooray, the car is back to normal. All the parts arrived last week, so Andy Bunyan took the car on Monday to fit them. There was a slight hitch with the wrong throttle position sensor being supplied, but the correct one was re-ordered and arrived the next day. I now have the car back and it's running perfectly. I haven't had the bill yet, but it's looking around £600 (if I'd taken it to a BMW garage, it would be more like £1,600).

Update 3 (24.3.14): The car is back with Andy. After it came back, the radio wasn't working. I thought it was a disturbed wire under the bonnet. Andy says it is a broken wire running into the tailgate, which is why the rear wiper, rear window catch and reversing light are also not working (the radio aerial is the heated rear window). Apparently this broken wire is a common problem on BMW Touring models (estates). It's a simple fix (new bit of wire) but it's a right royal bugger to get to.

Update 4 (28.3.14): Andy Bunyan replaced the wiring and I now have working rear wiper, etc. However, the central locking isn't working and the car won't open without using the key. This means that to unlock the car you have to dismantle the key fob, pull out the hard key, open the door (which sets off the alarm), then push the key into the ignition (which silences the alarm). Andy wondered if the battery might be out in the fob, but I know that something funny is going on because the on-board computer resets itself every time your start up.

Update 5 (31.3.14): So to give Andy the benefit of the doubt, I thought I'd replace the battery in the key fob. Now, you wouldn't think something like a battery could be so complicated! Google BMW key fob battery and you get back a mass of contradictory advice - some people say you can replace the battery, others say it's a sealed unit and it recharges itself automatically. I found a video on YouTube where a man replaces the battery in a 5-Series. It looked easy and the battery was the same as I'd just bought for the kitchen scales, but when I tried to follow the instructions, it was clear that our key fobs (although they looked identical) were different. His had a replaceable battery and would come apart; mine was a sealed unit. BMW UK and BMW USA obviously have different batteries. I called the parts department at Sycamore (the Peterborough BMW dealer). These are always pretty good (in fact the whole garage is pretty good, just massively expensive) and they said the key fob is sealed, it does recharge in the car, but they could supply a replacement key fob for £150.

Update 6 (2.4.14): The key was there next day and I had to take along my passport and registration document in order to get the key. It didn't work. The parts man called one of the engineers, who said it looked as if the central locking unit, which was sited near the tailgate, had been damaged. He said they sometimes suffered from water damage on estate models.

Update 7 (9.4.14): Have we finally made it? Andy took the car back. He said the central locking unit was water damaged. He repaired it and resealed it and it now works. The computer is also not resetting itself every time. Fingers crossed!