Audi A4 B5 1.8 se 1999 - Running problem

[Petrolheed82]

Hi guys, i have just joined the site. I am looking for some help and advice regarding my A4 B5 1.8 20v SE. It's a 1999 model with the APT engine. The car has always felt very under powered and sluggish. It will hesitate badly when cold.

If you blip the throttle it will backfire, and you can hear popping in the air filter housing. When you attempt to rev the car it will hit about 5000rpm then start spluttering and won't rev any further, almost as if the rev limiter has been hit.

I got the codes read recently. P0130 was the only one. After the garage read the fault codes, he erased them. Immediately after this the car was running far worse than ever before. It would barely hit 4000rpm and would barely take any throttle.

I took the coil pack off and checked the condition, tested it, it was fine. I disconnected the injectors one by one and each of them made a distinctive difference to the running of the engine. This tells me that all cylinders are firing.

All plugs look similar and are evenly coloured. There is a little black soot which indicates that the engine is running rich. The recent emissions test confirms this with a CO reading of 0.18% against a maximum permissible reading of 0.20%.

The last thing i tried was disconnecting the MAF sensor. Voila! The engine is running perfectly without it! revving right through the range free as a bird! The car has more power than i ever knew it could have. It pulls like a train. It gets to 4000rpm and hits that well known 20 valve power band.

This would indicate that the MAF is at fault. The car idles perfectly with the MAF connected, but disconnected it will not idle at all. I have to rev it to keep it running. I am not 100% convinced though, because the posts i have read indicate that the car should still idle without the MAF connected.

Any thoughts on my situation would be much appreciated! Thanks, Al.

[mikeybutch]

Seems certain that the MAF is duff

[Petrolheed82]

Thanks mate, it definitely makes sense, it's reassuring to get a second opinion.

[zollaf]

certainly sounds like your AMM (maf) is duff, but p0130 is a code relating to the lambda sensor, or oxygen sensor. there are 2 codes, either the actual sensor or the heating element, but you would need to see the rest of the readout to know. a poorly AMM wont always throw a code or put the MIL on.

[Petrolheed82]

Hi Zollaf, I have some more info that may be of interest to you. I looked up the P0130 code when the codes were read. When i disconnected the MAF the Catalytic converter started stinking beyond belief! It was awful......Smelt like a Vauxhall Vectra from the late 90s!.

This led me to believe that the cat was bogged down with old unburned fuel deposits from the months of rough running. It cleared after a good blast out the back roads. Do you think the same deposits could have triggered the pre cat lambda fault code also?

The other thing that is causing slight concern is that there is no engine management light illuminated on the dash when i turn the ignition on. I don't remember ever seeing it on. Do you have any ideas as to what could be causing that?

I have checked the fuses and they are all present and functional. I read somewhere that the 99 A4 may not have a CEL, is this true?

[zollaf]

the mil light should come on with the ignition and if all is well go out once the ecu is happy their are no problems. my initial instinct is that the mil (malfunction indicator light or engine management light) has been disabled in order to sell a car with an illuminated mil , which is obviously quite difficult and will de value it. this is sometimes done by rogues to save spending money fixing a potentially expensive fault, or to hide a simple fault through ignorance. the unsuspecting buyer doesn't look for a light thats not there, so gets caught out. you need a more experienced technician to diagnose your car but it is indicative of a failed lambda sensor which may or may not have destroyed your cat, and possibly also you AMM , although disconnecting it in this case is no confirmation of it actually being faulty. as said, the amm wont always trigger the amm, but the p0130 lamda fault almost certainly will. most professional scanners will give the mil status though, i.e whether or not the mil light should be on, or not.

[Petrolheed82]

Thanks for the reply mate, so you think that the light being out is possibly indicative a of failed lambda sensor?

Do you think that replacing the lambda sensor (assuming that it is faulty) would re-enable the light?

[zollaf]

no, the light has been disabled and should be illuminnated at least with ign on and probably all the time. first thing to do is to get it working. i doubt the bulb has been removed or a wire cut as its a pcb and not easy to get to. i would remove and strip the dash and you may find the problem. its possible something has been used to obscure the light, such as tape. its not something i have ever or would ever do to a car, so difficult to tell you how a rogue would do it
incidentally, someone who does know how to do it isn't neccessarily a rogue, but more likely a good pro thats had the same problem and solved it.

[phil miller]

hmm not happy, i sold a perfectly good AFM for this engine on ebay today for 99p gutted

[Petrolheed82]

Hi Zollaf,

just wanted to give you an update on the status of my running problem on the A4. We took it on holiday to Haven on Monday. I left the air flow meter disconnected during the trip. The car performed very well all the way there with plenty of power.

The most annoying part was trying to keep it idling by revving it while braking on approach to roundabouts etc. One thing i noted, was that at various points the throttle was a bit like a switch, performing beautifully when open wide. However, at random points, when cruising with it only slightly open, the car would stutter and lose power. To overcome this i just pressed the throttle down further and it jumped back to life.

Due to my unfamiliar surroundings, when we reached our destination i reconnected the AFM, so that the car would idle when stopped at lights etc. As soon as i reconnected it the car would run horribly again, popping and misfiring. At one point it would barely pull itself up a hill in 1st gear with the foot to the floor! It gradually improved and was driveable again but severely lacking power.

On the motorway home, the car started losing power terribly, in 5th gear foot to the floor it was losing speed to below 60MPH. I dropped into 4th and floored it, the car just kept losing power. I thought to myself "This is going to break down altogether!"

I pulled onto the hard shoulder and disconnected the AFM again, and away it went. With plenty of power. Sorry to drag this out but, do you think that the oxygen sensor could be faulty as well as the AFM? The reason i was curious about this was due to the hesitation with the AFM disconnected. What do you think?