Strange limp mode

[danielintheuk]

Hi folks

I have done a search and read the limp mode topics.

However what confuses me is it seems to be speed that makes it go into limp mode rather than load or revs?

I can drive it hard in 1st and 2nd gear to the redline, and it is pulliing well, However if I get it on the motorway , and accelerate really really gently, it goes into limp mode somewhere between 60 & 70 mph .
I have read the stuff about EGR valves, and I have looked at mine and it didnt seem to be excessively dirty.I have no idea how to check the egr valve is working as it should, but I would expect if the egr was sticking it would cause problems at any speed , and would be more linked to load rather than speed, so i cant see that to be the problem.


I have checked the hoses from air going in , right up to the manifold, thats all secure. The vacuum pipes are all good.

I have read the stuff about n75 valves and understand this is something which controls boost curve, so i cant see that to be the problem as I can give it lots of work to do in the lower gears and its fine, whereas pulling gently in 4th or 5th gear, i`m not really using the turbo much so dont see how something that controls the boost curve would affect it?

Any more suggestions ?


Thanks

Dan

[danielintheuk]

Bought the basic hand scanner today from eshrules....easy to operate and comes with a book with the fault code descriptions. Also it clears the codes if you want it to

I now have the fault code ..its 00575 manifold absolute pressure sensor .

Not sure what to do next as i have looked on the forums and it seems to be either the maf, a blocked up cat, the sensor itself, the n75 valve, or sticking turbo vanes.

Any suggestions appreciated


Thanks

Dan

[danielintheuk]

Think I may have sorted it

Looked up a pic of the sensor in question so I could have a look and see if anything obviously worng, e.g not plugged in. All looked ok with the sensor, however I noticed a vacuum pipe not connected to anything ? Contorted myself into several different positions to look where this pipe is meant to go, and voila .....it plugs into the boost pipe. Not sure where the pipe comes from , but it seems to have done the trick.... i still have some air noise which i dont think should be there .... but the car is pulling a lot better, and also I have just been on the motorway, doing all possible to make it go into limp mode , but it insists on behaving and staying in "normal mode".

I can post some pics up if this is of use to anyone, for reference The boost pipe i`m talking about is the one at the back of the engine, parallel to the bulk head, goes from intercooler to the inlet manifold .

Happy to report did a further fault scan with my new toy ( courtesy of eshrules) and no fault codes .

[nige123]

hi, any chance of some pics of the said pipe, as i have a 98 passat tdi sport with keeps throwing up fault code 00575. the car goes into limp mode intermittantly whilst accelerating in 2nd or 3rd gear at about 2500rpm and doesn't return to normal until switch off and back on again. also it doesn't seem to play up once the engine is up to normal running temp.
any help would be greatly appreciated
thank
nige

[danielintheuk]

hi nige

Will sort the pics out in a few days ..... I`ll try and explain better where the pipe was.

From your intercooler you have a pipe coming out at the top , if you follow this, it goes to a hard pipe ( not rubber) which is at the back of the engine, at the start of this hard pipe, there is a rubber connecting piece , and then futher along there is something connected to the pipe on the underneath ( which I presume is the map sensor) . Between these 2 points there is a bit which sticks out from the hard pipe , which should have a vacuum pipe attached. The only problem being its almost impossible to see . My advice is to have a very close look around that area and see if any pipes are not connected.

The symptoms you describe are different to mine as mine wasnt affected by temperature, but its still worth having a look at this area just in case.

Good luck and let me know what happens

Dan

[nige123]

thanks for the reply dan, i will check this out at first chance. it may well happen at running temp as well, but it just hasn't yet. in about a month of having the car its probably done it about 7/8 times and at all other times no probs.
thanks
nige

[danielintheuk]

Hi Nige , hopefully there should be a pic here now , I have circled the area where this pipe was. Hope this helps

Dan

[nige123]

thanks for the pic dan, i have replaced the easy access pipes and will try to do the harder to reach ones at the weekend hopefully with good results. i will post any results i get.
thanks again
nige