luckyI3

i'm just gonna tell you the whole story. my wife drives this car, the idle has always fluxed at least for a long while. she fueled it up with 92 bp as always (so she tells me). then it started like a half day later really surging from almost die to 900rpm but it doesn't do it all the time just when it feels like it. it will run fine and sit there and idle for 4 or 5 minutes then bam it starts surging. IT will surge for a minute or 2 then go back to regular flux idle. Also it will do it under load right around 2000rpm above 3000 it won't do it. thought bad fuel. so I ran alot of it out and put in some more from a different station back in. didn't help. I removed the tb cleaned all the gook out cleaned the intake hose replaced all the small fiber wraped vac lines and the larger plastic ones from vc with rubber hose and used a gasket sealer glue to seal them. alot of them were bad. put it all back together still has same problem. I bumped into maf when it was running fine and it started surging. so I do wiggle tests on connector and it does make it start surging. so I'm thinking maf is bad try unplugging it. That fixes it. runs great without it. codes tranny into safe mode, but runs good. so thats why I think its bad. also hooked vag-com up and watched it it pulls on average 5-7 g/s but will run all the way to 15-17 when it starts surging my tb angle is 2.8. rpm 740-800 the only thing that changes when it surges is o2, maf, spark retard, and injector delay. but what I don't know is if the maf is the problem or cure to whatever the real problem is. I wouldn't think wiggling the wires or jiggling the whole thing should make it surge like that. but I am being way more violent than anything it would see in service i.e. driving down a rough highway. the only codes it throws up are bank 1 and 2 too rich and knock sensors 1 and 2 too low or intermittent. it doesn't throw a code for the maf itself. could the knock sensors be bad? I doubt they both went kaput at the same time. this is a bone stock car. paper air filter and I run bosch p2 plugs everything is as it should be. does anyone know how to test the individual maf sensor with like a vom. I'm already tried cleaning the terminals and making sure there is a good connection with connector. could bad fuel have f'ed up something else? has anyone had this problem and if so what fixed it? what happened when your maf went bad? was it even close to this? I would rather not buy a (what do these cost) gazillion dollar maf if I don't need it. Please and thank you for your help.
also I did use a commerical maf meter cleaner on it and it seemed to improve it but it might be my inagation. Really I just need to know how to test a maf.

4Rings::G2 boosted::

Ok, first of all if moving the MAF wire is causing a change in the reading it's most likely a connection problem, it could be inside the plug but it also could be along the wire harness between the maf and the ecu. It might sound strange but I've seen cases where the MAF wires inside the harness would chafe against each other and expose the wires to the point where slight movement of the car would cause a change in the voltage reading. The only way to know for sure is to hook up a secondary set of wires bypassing the stock harness between the MAF and the ECU. It's only 3 wires so it's not hard to do, I can send you schematics that'd tell you which wires in the ecu harness to connect to.

Second thing to try is changing the MAF itself, you can get a reconditioned unit (new sensor in a used pipe) for around $75.

With MAF disconnected the ECU runs directly of the build-in maps. The fact that when the MAF is unplugged the problems go away is a good indication that the MAF or MAF wiring is your problem.

A health MAF should read around 5 g/s at idle and around 190 g/s (iirc) at redline with fully open throttle. You can log the maf readings with a vag to check if they are within these limits and also to ensure they rise linearly with rpm.

Good luck!

(Was this long enough of a reply? :P )

luckyI3

Yes this was plenty long, and I'm glad it was. who sells the reconditioned one. And please send me that wiring digram. Also is there a way to test the maf itself. Thanks for the info.

4Rings::G2 boosted::

log the maf with a vag if you want to test it<ul><li><a href="http://tomasz.data2net.org/audi.b5.wd.34.pdf">wiring diagram</a></li></ul>

luckyI3

I tested the wiring back to ecu and found a broken wire. fixed that but its still doing it not beeter or worse. I triple checked all the wiring again but cannot find any other problems. I have a new maf on the way and will be trying it tomorrow. I did log the maf with vag but it spikes when engine does just like I think it would considering the motor almost stalls then intakes a large volume of air to keep from dying. so that test seems pointless. I did notice that the singal wire ooutputs on idle around 1 volt it fluctates slightly but when the engine dies it still fluxes around just like when the engine is running. I'm pretty sure the maf is bad.

4Rings::G2 boosted::

this is particularly important if you unplugged the ECU recently.

The way to check the MAF readings is to log then as you accelarate to the redline in 2nd or (if you have the space and lack of cops) 3rd gear and graph the resulting log in excel. If you keep the throttle fully open during the accelaration the resulting line should be directly proportional to the RPMs.

luckyI3

got the new mass air flow and it's all better. The real tricky problem I was having is that even though I triple checked all the wires in maf harness for shorts the problem would persist when harness was wiggled. Installed new one and it wouldn't do that, so the maf sensor itself was acting like that way. But it really made it look like a wiring problem so beware of similar problems audi fans. I found the best way to test it without driving it around was to turn the key on and using a vom test from the signal wire (mines green) to ground and if you see it fluxating its probaly bad because the engine is not running so it should be constant. like the new one is it stayed right at .9 volts. It also helps if your vom has a min max record function so you can wiggle it and bang on without having to keep your eye glued to the screen. Thanks everyone for your input espically 4rings.

4Rings::G2 boosted::

good to hear. Sometimes the simplest explanation is the correct one.

audinutt

replace the MAF if your values are hitting 17 g/s at idle

neubert24

I'm running into the same problem where is the maf sensor located and is it possible to clean, any help would be appreciated, thanks.