jpp19 Posted September 8, 2011 Report Share Posted September 8, 2011 (edited) My tdi is going in to limp mode very regularly, especially when it is cold on a morning. Once it has been running for about 10 minutes it doesn't do it much at all. I have checked all the pipes and there are no splits and I've replaced all the vacuum lines. I have also just replaced the sensor on the pipe from the top of the intercooler going into the inlet manifold. I have 2 n75 valves (neither are brand new) but one clicks when the ignition is on and the other doesn't, but neither makes any difference to the limp mode.I have also changed the maf with a brand new one, but I'm abit confused with that aswell. After reading the tdi forums I'm under the impression that if the maf sensor is bad, when you unplug it it will either make the car run better or not make any difference. If i unplugged both the old one and the new one, neither made any difference to the way the car drove or the limp mode.Any help is greatly appreciated, cheers edit: forgot to add that I put a new Turbo on when I first got the car aswell. Edited September 8, 2011 by jpp19 Quote Link to comment Share on other sites More sharing options...
georgen Posted September 8, 2011 Report Share Posted September 8, 2011 once came across something like this with another make of car, mainly did it when cold if booted, did it a couple of times when hot booted, in the end it was a semi blocked fuel filter, dont ask me how it affected it the way it did, but was changed and problem went. its cheap and worth a try if its been a while.George Quote Link to comment Share on other sites More sharing options...
jpp19 Posted September 8, 2011 Author Report Share Posted September 8, 2011 Cheers for the info, I gave it a full service about 500 miles ago so shouldn't be that but i might check all the fuel lines and that. It's really strange the limp mode, there's no consistancy to it at all, it sometimes goes in going down a hill, so not just under load like most cases : /Cheers Quote Link to comment Share on other sites More sharing options...
Derv Posted September 8, 2011 Report Share Posted September 8, 2011 If it is going into limp mode it show throw an error code. Quote Link to comment Share on other sites More sharing options...
Cannonball Posted September 8, 2011 Report Share Posted September 8, 2011 Yes, get the stored code read and go from there. If its a lottery I'd throw a wild guess at the Temp switch, but if you dont get the code read you will be chasing your tail for weeks looking at things. Quote Link to comment Share on other sites More sharing options...
jpp19 Posted September 9, 2011 Author Report Share Posted September 9, 2011 (edited) Yer I've stuck it on the Vagcom and when it is in limp mode it throws up p1556, charge pressure negative deviation. It doesn't log a code if I check it when it isn't in limp mode, and I've already changed the water temperature sensor, it didn't seem to make any difference . I'm thinking it must be a leak somewhere so I'll try and do a pressure test on Saturday see if that helps.Cheers : ) Edited September 9, 2011 by jpp19 Quote Link to comment Share on other sites More sharing options...
durb Posted September 10, 2011 Report Share Posted September 10, 2011 I know we are not VNT, however the following thread on another forum suggests it could be MAF.http://forums.tdiclub.com/showthread.php?t=215165Durb. Quote Link to comment Share on other sites More sharing options...
jpp19 Posted September 10, 2011 Author Report Share Posted September 10, 2011 Cheers for that mate, it's got me thinking I might have got a bad maf then, I've read about people getting duff ones before. I took all the Turbo and all the pipes off today and tested them and there are no leaks or anything. Could it also be the n75? I took the vacuum pipe off which goes to the wastgate, and that made no difference, still drove the same and didn't go into limp mode when hot. Surely it should just overboost if the wastegate won't open?Cheers Quote Link to comment Share on other sites More sharing options...
durb Posted September 11, 2011 Report Share Posted September 11, 2011 Would have thought that disconnecting the wastegate would result in overboost, and hence fault codes etc.From membership of another forum (non-VAG) sometimes if the MAF is utterly buggered, then it can have the same effect as unplugging it. hence no change by unplugging. could it be faulty wiring to the MAF? Quote Link to comment Share on other sites More sharing options...
jpp19 Posted September 12, 2011 Author Report Share Posted September 12, 2011 (edited) I know that's what I thought aswell, I know it's possible that's it could be a faulty maf, you just don't expect it from a new part. No i dont think its the wiring we have checked them all and it's getting power from the battery, and there's continuity between the wires from the ecu to the plug on the maf.I tried to get some maf and boost logs off Vagcom and either I'm not doing it right or it's showing the problem, as the graphs, especially the Turbo one looked nothing like it should, there was no spike it just seemed to gradually increase. I'll try and post them up later. I'm gonna check the cat tomorrow to make sure that's not blocked, cos I think that could affect boost, and there is also some smoke coming out the oil cap and dipstick when you take them off. Cheers. Edited September 12, 2011 by jpp19 Quote Link to comment Share on other sites More sharing options...
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