1.8 A4 intermittant engine fault, worsening, HELP!

**bannedbiker** · 27-07-2010,09:20 AM

Hi guys,
I've got a P reg A4 avant, the 1.8 normally asperated and I've got a problem with it missing.
It started about a month ago, it would only do it when cruizing the motorway and would just slightly stutter now and then. This has got progressivly worse and it has now started missing properly.
I've had the plugs out and they all look a nice tan colour, although 3 and 4 look nicer than 1 and 2!
My plan is to go through and replace the plugs, coils and leads as well as checking through the air system.
I was just wondering if this was at all a common problem and whether there was a good order of replacing things without spending a fortune?!

Cheers

**iwaters** · 27-07-2010,09:35 AM

It would be usefull to get the engine fault codes read first as these may help you to pin point the problem. Do you know anyone with a fault code reader or VAG-Com who can do this? If you don't it might be worth getting a local garage to read them for you for £50, or even better buy your own code reader from Ebay. The cheap ones aren't great but will do. Post any error codes you get here and someone will be able to help.

Other than that, your plugs sound ok, but they only cost £1.50 each so if they haven't been changed in a while start there. Next inspect the leads for signs of the insulation cracking or spliting, also where the leads run together or close to the head check for signs of arching, this will show as a shiny glazed spot on the leads. If you spot any of this then change them.

I wouldn't start replacing coils or anything like that unless you are sure they are faulty as that could get very expensive.

**bannedbiker** · 27-07-2010,01:42 PM

Hey dude, cheers for the response.

I dont know anyone with a fault reader. Is it worth picking up a cheap one off ebay? how little could i get away with spending on one?!

Yeah, I was planning on doing the plugs first as they're nice n cheap. As far as the coils and leads go, mine are integrated. The coils sit above plugs 1 & 2 & then the leads come out for 3 & 4. This kinda put me off the track of and electrical fault as it was 3 & 4 plugs that looked the worst!

Where would I find out which engine code mine is? I've had a quick look around the engine bay for the VIN plate expecting it to be on there but I dont appear to have one, my chassis no is under my windscreen!
I looked at the prices of coil packs on the GSF website, it's either gonna be £21 or £118! If its only £21 I dont mind changing it to eliminate it being a possibility.

Again, thanks for the help.

**iwaters** · 27-07-2010,02:00 PM

The best diagnostic software is called VAG-Com. There is actually a shareware version which is free which will probably suit your needs. You need to buy a cable but there are cheapie jobs on Ebay for about £14, you will need a laptop or a very long USB lead! The shareware version lacks some functions but you should be ok, if you want the full version you can upgrade for £50. Look at http://www.ross-tech.com/

If you don't have a laptop you can get a hand held one. This one is £27

http://cgi.ebay.co.uk/VW-AUDI-Diagno...item45f174fa16

Most garages will charge more than that to read them once!

The engine code is stamped on the engine somewhere, I am not sure where it is on the 1.8, otherwise where the spare tire is in the boot there should be a white sticker, this will have the engine code on it near the top. It is a 3 letter code, e.g. AML.

**bannedbiker** · 27-07-2010,02:30 PM

Cheers dude, you're a legend!

I do have a laptop but only have access to the net here at work, downloading things aint possible so I'm gonna buy the handheld one you suggested, a lot of my friends and family have VAG cars so I'll start charging them in beer to read their faults!

I'll go have another look for my engine code in a while.

I'll probably be back in a few days with some fault codes for you to advise me on!
Thanks muchly, well helpful!

**bannedbiker** · 28-07-2010,08:55 AM

I found my engine code exactly where you said in the boot last night, I have an ADR engine, unsurprisingly enough the coil pack for mine is £118 not the £21 one!

I'm kinda hazarding a guess that its gonna be something in the air system now though because the problem seems to be worse when the weather is at it's hottest (the oxygen content at its lowest).

Ah well, hopefully find out in a day or two when my fault code reader arrives!

**bannedbiker** · 29-07-2010,09:16 AM

Right then guys, advice time again!
I got my fault code reader last night and the results are as follows:

ABS: No codes
A/T: Linking Error (does A/T stand for atuomatic transmission?)
SRS: 00532 - Supply Voltage (B+)
Eng: 16507 - Throttle position sensor A circuit-High voltage input AND 17978 - not listed in my book of faults!

So, the way I look at it is that my TPS is knackered in a kinda closed circuit way. The 16507 fault is telling me that the TPS is giving a higher voltage than expected and the 00532 fault is telling me that a sensor is giving a higher voltage than expected (the TPS).
Is that right?!

What is the fault 17978?
I do have an "Insp 1" indication on my dashboard as when I bought the car it was serviced for me, around 1.5k miles before it was due, so as it ticked over to 80k it reckons it needs a service its already had! Is this the code to reset the inspection indicator?!

Thanks in advance for the help!

**iwaters** · 29-07-2010,10:05 AM

17978 is Engine start blocked by immobilizer. Don't think it is anything to worry about, it just means at some point the immobilizer cut the engine out, could of been years ago if the codes have never been cleared. I get the fault code up occasionaly.

The Service indicator can be reset manaully. I think (from memory) you press and hold the button on the left had side of the dash (the clock adjust) whilst turning on the ignition, it should now display OIL, then pull the right hand button until the service prompt clears. If that doesn't work try it the other way round: With the ignition off, push the right button
Turn the ignition on and then pull the left button.

The 00532 code looks like it relates to the airbag system, it usual indicates a problem with the wiring to or from the control module. I personally wouldn't touch anything to do with the air bag system.

Now on to the Throttle position sensor A circuit-High voltage input error. This is probably what is causing your rough idling. Again this is likely to be caused by a problem with the wiring. Check all the wiring and connectors to and from the TPS. Check for breaks or it rubbing against other components. If you have a multimeter you could test the voltage at the TPS (ignition on, not engine). It should be less than 4.5 V and should be steady. It is going to mean a lot of crawling around under the dash and in the engine bay. Look closely at where the wiring comes through the firewall into the engine bay, check the connectors for corrosion.

If you don't see anything wrong with the wiring then it could be a duff TPS, but I think you need to confirm the wiring is good before shelling out for a replacement.

**bannedbiker** · 29-07-2010,10:14 AM

You guys and this forum rules!

Thankyou muchly, I'll go through the wiring this week end.
Am I right in thinking the TPS is just a simple potentiometer? So therefore i could not only check the voltage with the igition on/off, but also disocnnect it and chack the resistance across it and that it cahnges with the position of the throttle?

**iwaters** · 29-07-2010,10:17 AM

Yes worth checking the resitance across it with changes. Also check the resitance and then give it a little shake. If there is any shorts or loose wiring then the resitance will change as it is being shaken