I hope this guide might help someone else on the forum if their VAG diesel (or maybe petrol too?) won't start but the battery, starter motor, alternator and fuel pump are OK.

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My 2002 octavia wouldnt start the other day. AA came out. Car would try to turn over, and try to start. Cranking it for 10 seconds still wouldnt start, almost like it had no fuel or was actually flooded with fuel (ie. no compression in the cylinders)

AA chap looked it up in his computer. It was actually a very dirty throttle body, which had caused the throttle valve to stay shut when i had switched off the car. Therefore when trying to start the car, no air was getting into the engine and hence it wouldnt start.

He removed the whole throttle body (5 minutes), see picture 1. And he cleaned it with "carb & choke" cleaner (available at halfords etc).

Lots of black sticky gunk, oil mixed with soot from the EGR valve had caused it to sieze.

You can manually open the valve by pulling out the plunger on the left side in Picture 1, this opens the valve again and allows the engine to start.

So, if your diesel sounds like it has no compression, has an OK battery and is trying to turn over but will not start, check that the plunger is up, and try giving it a tug.

To fix, remove the throttle body (which is the whole metal valve body, about 6" long - not just the round EGR valve on the top!) and clean it with carb cleaner to remove the gunk. Ideally, you should submerge it in the cleaner for a few hours. Hope this helps someone!

Picture 1 = the throttle body, with the round EGR valve on the top.

Picture 2 = shows the gunk inside the throttle body when the EGR valve is removed.

N.B. this is Not my vehicle pictured, mine was no where near as bad as this car, but you get the idea!

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Edited 4 May, 200917 yr by Gunswick

Just happened to mine, wish I'd read this before I called out the RAC man though lol, I'd thought it was the blooming ring gear on the flywheel, as it was spinning so freely.

thanks

Neil