Misfiring v5 Bora

[Marshthedarsh]

Took it in to a VW specialist today, and he's not sure what's causing it either. Straight away he noted the horrible idle, said they were all a little rough - but this was too much.

He noted that it seems to only be misfiring at idle, and his vagcom wasn't getting a misfire - only the oxygen sensor, yet he says it will usually come up when you do a check. Car does drive quite nice when warm and in motion, but has a bad idle.

He said that the MAF seemed fine, and it probably wont be the ECU because if it's bad, then the car won't go at all.

Like you Crasher he said the first thing to do was get the pre-cat changed as it was the only code. I'm guessing if it's bad it will improve the idle and mileage, though I'm not sure it's gonna fix the misfire. If it only misfires at idle as he suspects - then does the ECU play any part in the issue?

His workshop is at the bottom of a steep hill - so from a standstill it's a very bumpy and squeaky ride up. No charge for all his troubles though.

[Crasher]

The mixture is set by the ECU at all times using information from, the lambda sensor so if that is FUBAR the ECU will not have a clue what is going on and may under or over fuel and that will make the engine run rough, he could have checked this with a simple tailpipe 4 gas emissions test to check the O2 level.

[Marshthedarsh]

Ordered a new Bosch Pre-Cat. Before getting the installation sorted, I went and scanned the codes again: still getting 00525 - but 00635 has been replaced with 00553. I believe that's relating to the MAF, and the code has come out of nowhere. Only two codes I get, and when I clear them they both come back after a short while.

When the car is idling and I unplug the MAF - there's a little judder but the car goes back to how it was when plugged in. Same when I plug it back in, so the car reacts to it plugging and unplugging - but each side of this the idle and engine is consistent.

I've read that the MAF could be bad if it runs better unplugged, but it just runs the same. Does that code mean the MAF neads cleaning/replacing - or is it strange that this code has appeared out of nowhere and 00635 has disappeared.

I'd still think the O2 sensor is bad though. Exhaust has a light chug chug, and is pushing out big puffs of invisible air.

Mileage I'm getting is pretty horrible too. Onboard display just changes all the time according to how hard I push the gas vs how far I'm going - but seems to settle at 4ish km per L every now and then = 10 MPG.

I'm only driving around backstreets to see how it goes, but from last "Please Refuel" to current "Please Refuel" - 13L got me about 50km.

[Crasher]

Stop unplugging the AMM and code 00553 should stay away! I have been trying (in vain) to stop people doing this for years. Unplugging it and what happens means nothing.......

[Marshthedarsh]

Cheers for that. I don't make a habit out of playing with the MAF - so the code must have come from when the guy was playing with it. Code hasn't come back.


UPDATE - So I bought a cheap Used ECU - and when I plugged it in I now get all 5 coils sparking. So I'm pretty sure we've found the problem.

Of course the car only starts for a second because of the immo - but it certainly sounds so much better than it did with the old ECU. All electronics working.

So is the process to get a new Transponder chip as simple as it would be to get a spare key? Or do we have to go through the Dealer because the ECU has been switched... Cheers.

[Crasher]

Here we have a mobile chap come round and do this for us in his van, if you do not have this facility it may be easier to take the car to a VW dealer and ask them to code it in.

[Marshthedarsh]

Managed to plug in VAG COM and reset the Immo to 00 so it matches the current key. Immobiliser light no longer flashing and car starts up just fine with present key. Will go for a proper drive in the morning and assess the 02 sensor then.

Cheers for all your help Crasher


For anyone reading this in the future for help:

Car had a dodgy Ignition Amp, that was the problem - so get a replacement. We made it worse by playing inside the Amp which damaged the ECU - and it only ran on 4 cylinders instead of 5.

What solved our additional problem was another ECU, then reset the code with VAG COM so the key matches.

[Crasher]

Re-matching the ECU like that hardly ever works for me, I can remember one was a Golf 4 1.6 AKL but later stuff, no chance. Admittedly it is not something I try very often as we hardly ever have to chnage ECU's.

[BravoMalaga]

Hello Crasher,
I own the same engine in a golf 2.3 and I am "glad" to see I am having exactly same troubles than you. How did you fix it?
I thought it was going to be the ignitions coils and I just order it before reading your post.
Will I need to change the ecu and program the ECU?
Thanks a million for your help

[Crasher]

What is the cars year and engine type code?