2005 Fabia VRS. 70K miles. Original ASZ engine was replaced with new ASZ base engine, turbo, EGR, intercooler in 2007 - these bits have done 43K miles.

Engine runs ok but CEL light on.

My son has the car in Lowestoft now and took it to a local garage there.

Diagnostics say :

Fault 19551; valve for intake manifold flap N23 open or short to ground - sporadic fault.

Fault 17664; sender for coolant temp G6 short to earth - sporadic fault.

Today I checked all electrical connections and they seem clean and OK.

Engine runs with temp just over 90 centigrade

Engine idles at 900rpm. This seems slightly high to me. Could it be due to a coolant temp sender fault ?

I cant find valve N23. There are no electrical connections to the combined EGR/anti-shudder(changeover) valve , only to the vacuum distribution block.

I pulled off the vacuum hose connector block so I could then apply suction to each hose . The actuator for the anti-shudder valve (which I presume is equivlaent to N23) moves fully when I suck on it but it doesnt move when I stop the engine with the key. The valve seems seems to be open all the time - is this correct ? I dont think it is.

The EGR valve further inside the same housing moves a few mm when suction with a 50ml syringe is applied to its hose. Its all pretty gummed up around there with the usual thick black sludge. Should it move more than a few mm ?

I also note that the electrical connection to the vacuum distribution block are not matching - the vacuum block must have been replaced at the same time as the engine but with a newer unit requiring a plug of slightly different shape as the original still on the car.It fits but Ive had to cut a bit of plastic off so that the retaining clip works. I presume the electrical connections for this vacuum block are same as the original one. Is this correct ? I hope so its been running like this for 4 years ! But I must admit when I think about it the replacement didnt stop as quietly as the first engine - but not like something is terribly wrong sort of thing though . Could failure to activate the anti-shudder valve have been there all this time ?

My plan is to replace the coolant sender unit.

But I think the ant-shudder valve is not working but the problem does not appear to be with the actuator. I will remove it and clean it out.

Anyone got any helpful suggestions ? Anyting will be gratefully received.

Edited 7 August, 201114 yr by Jules59

I suspect you need a new coolant temp sensor, and check the thermostat as well. Also a new EGR/ASV valve or a good clean of the current one, if the diaphragms are Ok and not leaking (can hold applied vacuum with no leak down).

As for the vacuum control box, if the plug doesn't match, it's the wrong box, yuo may have one for a BLT engine, and the internals are different.

The vacuum box actually contains three solenoids, n75, n118 and n23.

Thanks

Im beginning to think the Skoda dealer put the wrong vacuum box on 4 years ago and N23 isnt working and in fact never worked.

I'll pop into to a different dealership to check this out.

How much are these vacuum boxes ?

Does anyone have part numbers for the vacuum boxes for the ASZ and BLT engines ?

About £130.

Do the hoses have the same connections on both vacuum boxes or are they in different positions. I note the hoses are numbered.

All better now.

Replaced coolant temp sensor - very easy job once I had viewed it wit a mirror and worked out how it was held in place with the plastic U clip.

I replaced the vacuum box with a new one. when I picked it up (£160 inc VAT) I questioned the Skoda dealer about the possibility of the wrong one being installed 4 years ago. He was adamant that the vacuum boxes were all the same. I couldnt be bothered to argue. There is an obvious difference in the electrical connections of these 2 boxes (new one on the right). Part Nos are different too.

And guess what, the changeover valve works. The way the engine now stops without a judder confirms this has never been working since the Dealer engine transplant.

Whilst I was as it,I dismantled and cleaned the the EGR valve/changeover valve assembly.