EGR Valve woes.

The tax man

Poorly running engines seem to be a common theme today on Motors.:D

Anyways if anyone could shed any light on this problem I'd be grateful.
I've a MK4 Ibiza 1.4 petrol engine (BBZ). Engine check light has been lit up on the dash for quite a while now. Dropped into my mechanic just to check the cause and the diagnostic code reader showed an EGR valve fault. He cleared the light and said it'll probably come back on soon,which it did 2-3 days later.
Car was in for a service two weeks later and he said he'd try and clean any carbon build up. At worst it'll need replacing. After service and valve clean out, check light was off but car ran a bit rough and before I was home the light was back on. Next day car was running smooth again so knew it wasn't a major fault just the valve needed replacing.
No issues with my mechanic,he was straight up with me,if trying to clean any carbon build up didn't sort it,the valve itself could be faulty. Seems it's a common issue on the Ibiza.
Left it at that for a couple of weeks,car was running grand just the damn engine light was annoying me. Got a diagnostic reader myself (not Vag-Com) and cleared the EGR fault code. Engine started running rough at idle but over 2,000rpm was ok.
Went for a short drive just to see if the engine light would come back on but it didn't. The next day I started the engine and it was running even rougher so stuck the diagnostic reader back onto the car and now I've a misfire on cylinder #1.
Since getting the misfire code I've replaced the EGR valve,was planning to anyway and while it ticks over at idle a bit smoother it's still misfiring at any rpm. I haven't driven the car at all since the misfire started just in case.
Sorry for the long background story but I'm wondering why clearing the EGR fault code(before replacing the valve) could have caused the misfire,it's been cleared twice before I did it and nothing like this happened.
I haven't checked the plugs yet due to lack of correct size sockets and torx bits but I presume that's the next port of call.Some sort of build up on one of the plugs? Can EGR faults go on to cause misfires?

Thanks for reading.

Mr.Diagnostic

Firstly, not all egr codes are caused by the egr valve. In your case it probably is the egr valve as it is such a common problem on that engine.
The car would run rough after the codes are cleared because the management system adapts to try and make up for some faults and this adaption is cleared along with the codes.
The misfire problem is probably not connected to the egr fault at all. It is either just a coincidence or you disturbed something while fitting the new egr.

The tax man

The car would run rough after the codes are cleared because the management system adapts to try and make up for some faults and this adaption is cleared along with the codes.

Yeah was told that alright hence the short drive after clearing the code but the system didn't seem to re-adjust itself.

I got the misfire before changing the valve so I don't think I disturbed anything. If plugs look ok or change of same does nothing,would it be wiser to stick the car on a trailer rather then drive 3 miles to my mechanic just in case the cause of the misfire is a bit more serious and not connected to the EGR end of things?

Was hoping to get a reply from yourself Mr.Diagnostic and you were in like I light. Cheers.;)

Mr.Diagnostic

The tax man wrote: »

I got the misfire before changing the valve so I don't think I disturbed anything. If plugs look ok or change of same does nothing,would it be wiser to stick the car on a trailer rather then drive 3 miles to my mechanic just in case the cause of the misfire is a bit more serious and not connected to the EGR end of things?

Sorry, I misread that. I thought the misfire had occurred after the new valve was fitted.

You mentioned it was serviced. Did it get new plugs then? Maybe check they are the correct ones. Misfire codes on these are usually a coil. Simply swap the coil from the cyl with the code with any other and see if the fault moves too. It is also possible to get a faulty new plug. If moving the coil does not cause the fault to move then swap two plugs around.

You are correct to not continue to drive it but it should be ok to drive it 3 miles to your mechanic.

There are a number of possible egr codes. Mostly on your engine the code is for egr position. The ecu can monitor the actual position of the egr versus the position it has commanded. This code is 99.99% caused by a faulty egr valve (Not all egr valves have this feedback facility). Other egr fault codes can be caused by outside influences and would require further investigation.

The tax man

No plugs changed on the service just gone.
I'll try that swap on the coils and plugs to see if it moves the misfire to another cylinder,if not it's garage time.
Thanks again Mr.D