What's wrong with my VW Polo? The engine management light keeps flashing.?

I took it to a local garage twice who could not work it out, they said its a random misfire but couldn't work out why it was misfiring. They changed spark plugs and leads and managed to get the light out. When I started driving it came back on so I took it to VW. They said same thing and throttle body dirty causing a fault so they cleaned it and said my exhaust is blowing (will cost £200+). My light was out again until when driving home it started flashing again. Would this flash because of exhaust or what else can it be? If a local garage and a VW dealer do not know what is wrong what else advice does anyone else have for me? Any help whatsoever is appreciated, especially from mechanics etc.

Answers:
Sorry I don't know how old or how many miles your car has done but here are a few tips anyway:

If you are misfiring then there are only three basic things that can cause it.
1)Lack of fuel
2)lack of compression
3)lack of ignition ie spark.

Blowing exhaust won't cause any of these three but will cause loss of power and efficiency.

If your car is multi point injection and has at least one injector in each cylinder, which I guess it has, then I would check that the injector is connected and working properly. Injectors do tend to stop working on occasions especially with high mileage, but doesn't have to be high mileage.

Lack of compression can be due to damaged valves, bad tappets/valve clearances, or bad cam shaft timing. If you haven't had your cylinder head worked on or had a timing belt breakage/change then these most probably aren't causing the problem.

Another cause of lack of compression in old or high mileage engines could be a damaged or worn head gasket. If your head gasket has gone and is causing lack of compression then there may be a "blowing" sound from the cylinder head area and may also be waxy oil deposits in your coolant water, and/or smoky exhaust fumes.

Did they change the distributor cap and rotor arm if your engine has one? Look inside your distributor cap, if the electrical terminals are black and pitted then its time for a new one as well as a rotor arm.

I would also check the electrical connections around the engine to make sure they are not damp, damaged or corroded. Especially the ones associated with the Engine Management Unit.

If all that fails then I would suspect the EMU itself is not working right. and probably needs replacing.
If its still running alright, the old saying goes, if it ain't broke, don't fix it
I had the same problem with my renault clio. the engine management system light kept comming on and causing the imobiliser to activate. i took it to renault and after testing they found broken wires leading to the EMS. that would explain the intermitant fault, cost me £280 most of that was the diagnostic tests. get someone to look at the cars electrics.

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