All Things Mk5 > How to Guides / Troubleshooting

p0299 underboost

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cutchie:
Anyone ever seen this fault when it's not pcv, dv or intercooler pipes? According to some logs I ran demanded boost was 2000mbar and I was only producing 1300mbar? And for referance my maf reading is 130 g/s peak.

Car also has a decat downpipe and pops and bangs loads but stopped when I disconnected the maf.

Can anyone help I'm dying to get the car mapped to the stage 2 that I've got the bolt on mods to hit

pudding:
Going by those numbers that's 4psi and 162hp.  It must feel pretty sluggish?

It's either a massive boost leak or an N75 / wastegate problem I'd suggest.

cutchie:
Well my last car was an in between car, 1.8tds fiesta so anything would be quicker but yea it feels like it's holding back! I can't find a boost leak, I may change the intercooler to the s3 type to rule that out, I might try and replace the n75 valve but I hear it's a nightmare thanks for the reply.

pudding:
I'd expect to see a fault code for the N75 though.  "Set point not reached" or something like that.  They do fail though, so might be worth changing, and yeah, it is a pig!

cutchie:
The fact that it's popping so much makes Me think it could be the  wastegate (but I'm no expert) it could literally pop 10 Times on over run! Sounds good but it's Defo not right lol

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