Hey all.

My 1999 mk4 golf gti-turbo (agu engine) has had a fault since I’ve had it and myself, or the dealer have been unable to rectify it. To give you a brief idea of the fault, the engine power violently cuts (like fuel cut) when it’s either under load, ie; a hill start or quick get away from standing, or as you back off the throttle when over taking etc. The vehicle also seems to be underpowered and a boost guage shows no more than 5psi which drops off to almost 0psi at about 5000rpm. The fault code it keeps coming up with on vagcom is “manifold absolute pressure limit exceeded”. Now being a fully trained technician and having it looked by a friend who is a master tech at V.W, we have been totally baffled by the cause after testing and replacing the following;

• New K03s turbo (old unit had a large crack through to wastegate)
• New airflow meter and wiring checked as far back as possible.
• Tested N75 boost valve (Originally had no power to it, found the feed off the fuel pump to be faulty – repaired, problem still present.)
• New water temperature sensor.
• Replacement E.C.U fitted and coded.
• New exhaust system including De-cat, in case cat blocked.
• New Forge re-circulating dump valve.
• Removed complete boost system and intercooler and checked for splits/breaks/damage etc – no faults found.
• Fuel system/pressure checked and new 4bar pressure regulator fitted.
• Checked for map sensor and wiring, but no map sensor fitted to vehicles of this age.

 If you guys have any ideas I’d be extremely grateful, however I’m also considering having a 225 bhp TT conversion done on it and was wondering if anyone knew of any major problems that would urinate on mt bonfire!!!

Thanks in advance peeps.

Also, would anyone with an early agu engined mk4 be able to take a pic of the correct plumbing for the dump valve and n75 valve please? I know i'm a pain dudes but i really want the car right and if it's a simple pipe on the wrong way it saves alot of hassle.

Thanks again peeps.

 The big nipple from the N75 will be fitted inside the intake hose.

the opposite to the big one, will be to the wastegate.

 Thanks for that mate, appreciate it.

You could swap out the ignition amplifier with a known good one, if you can, when mine was dying it caused no end of odd running issues.

Vag-Com sas the following on their wiki concerning issues about that error (three links come up in the search depening on the type of fault, have a look at each)

http://wiki.ross-tech.com/index.php/Special:Search?search=manifold+absolute+pressure

EDIT: I didn't think MAP sensors were on AGU engines?!

 Thanks fellas.

 AGU engine's don't have a MAP sensor, so you best check your engine code, you must be wrong some where. If you have got the wrong engine code, perhaps swapping out the MAP sensor is a good starting point.

No, i meant i looked for a map sensor but then found out the early agu's didn't use one so that side of things must be fine.

Thanks again dude.

 So are you getting any errors via vagcom now?

 I use to get a very very similar problem with mine, but it went away on it's own!!!! As did pope on here, and again, his just dissapeared!! Hope you get it sorted mate.

One thing that has been known to cause a similar fault though is the wire loom to the coil packs shorting somewhere. Might be worth removing the insulation and re-wrapping them IMO.

Andy

 Cheers guys.

I have checked the coil pack wiring but i think i'll go further back now that you've said it andy. Vagcom just keeps coming up with manifold absolute pressure limit exceeded. It's a very strange fault that doesn't make a hell of alot of sense and it will probably turn out to be something daft, but thanks for the reply's, they are appreciated.

 That's the same code mine was throwing up. I wish I could be more use as I know how annoying it is.

Did you do anything to trigger it? e.g. remp, replaced something? Random as it seems have you tried cleaning your throttle body?

Andy

 Nothing at all no. To be honest with you, the car had the problem when i came across it and i was convinced it was because there was no power to the n75. How wrong could i have been ............................................

Throttle body has been removed, cleaned and reset yes. The biggest sh1tter about this is that i'd just put the money in place to have it fully painted and uprated as i love the car to bits, but there's no point if this problem isn't going to show itself. The only other option is to convert it to a 225bhp lump and replace the loom too. Alot of work which i don't particularly have the time for at the moment tho.

Having done some reading around forums (out of curiousity), it seems the AGU might well have a Barometric pressure sensor (BARO) instead of a MAP sensor, this along with data from the MAF and intake temperature allows the ECU to calculate manifold pressure.

Are you chaps using a shareware version of VAG-COM or an upto date version? It's possible the older one gives the wrong details for the error code, maybe a newer version is more acurate.... (note: clutching at straws ;) )

 Yeah, i think it's the unit on the bulk head to the right of the air box. I haven't actually replaced this, so i may try one if i can get hold of one. I've been using vagcom at my local dealer as i used to work there so assuming the techs are carrying out the updates, then it should be up to the minute.

Thanks again Matt.

Vag-com will refer to it as a "Manifold / Barometric Pressure Sensor (G71) / (F96)", MAP(G71) sensor and BARO(F96) respectively, I think lol. I'm sure the dealer is correct then, just wondering as I'm no expert at all :D

Barometric Pressure Sensor
VAG: 853 919 562 
Bosch: 0 280 101 001

 Top man!

To be honest, i'm not convinced the dealer is sure as it's a long time since they've loked at one of these early ones. I have a mate locally who has loads of vw experience and all the diagnostic kit known to man it would seem so it's off to him for the final effort.

Thanks for all the help dudes, it's nice to see people still help each other out - respect is due!!!

 hi. i have a 2000 1.8t. i've just installed a dump valve and a full induction kit. now when stood ticking over the engine hunts like mad, the rev counter bounces up and down and when i stop the engine stalls. please can anyone help???

 ^^ might be worth making a new thread with your problem in buddy :)

 sounds stupid but are you sure its not a pin hole in a boost hole or the intercooler damged sounds like its boosting then just letting go of the preasure ?

 All boost pipes and intercooler have been pressure tested gricey.

Bit of an update though, problem may, just may be sorted. After reading up on the barometric pressure sensor, i decided to dismantle it and found that someone had been in there and totally screwed the workings up. I made a tempory repair and the problem is now 97% fixed. New part ordered for tuesday, fingers/legs/and all other limbs are crossed!!!

Oooooo Pics! :D

 This is some seriously usefull info, as that's now the first thing I'll check if my problem raises it's ugly head again. If I can remember what the heck it's called and figure out where the heck it is lol.

Andy