how much intake buildup before overboosting?

Almost titled this "the tale of two limping unicorns"
I have two nearly identical cars with the same problem (overboosting). Both pass MAF, N75 tests, vacuum tests and VNT start/stop pressures (one is a little slow to move at first, but returns quickly).
Both will overboost at higher RPMs, especially in 4th gear.

My buddy and I both have 2003 Reflex Silver ALH 5sp GLS wagons - only differences is his has black leather and traction control with 225k miles, mine has grey leather with 304k miles.

I had him come over last weekend to diagnose his limp mode. I figured something would come up quick, but everything passed the tests. I searched for the lesser known causes to overboosting and came across clogged intake or exhaust. I almost ruled them out.... I put a new downpipe/cat on his car maybe 30k ago. I also did the last timing belt and a full intake cleaning (including the ports in the head and EGR) maybe 40k ago.

I pulled the EGR and there was maybe a little over 1/4" of buildup, but figured I'd clean it while I was in there. I reached in with a bent over screwdriver while vacuuming and cleaned what I could and reassembled.
I could not get it to overboost again. I did a full throttle 1st through 4th blast on the highway in the exact same manner/place as when I was logging it and easily caused limp mode.

If this was enough to cause the problem, I can only imagine what mine looks like!!! (Purchased with 303k, in limp from bad MAF - I did the last 2 timing belts but never cleaned the intake. VW rebuilt the motor around 100k when the timing belt broke so maybe it was cleaned 200k ago?)

I would think VW would have put on a clean intake, but then again, I would not be surprised if they didn't.
What strikes me odd is I've read anecdotes that a dime-sized hole through the crud should still be "OK". Not that I'd want to drive like that.
At any rate, 1/4" over 40k seems like some pretty dirty fuel, OR at least sub-optimal combustion?
That's a head scratcher.
I'd be interested to see what yours looks like myself lol

STDOUBT said:

I would think VW would have put on a clean intake, but then again, I would not be surprised if they didn't.
What strikes me odd is I've read anecdotes that a dime-sized hole through the crud should still be "OK". Not that I'd want to drive like that.
At any rate, 1/4" over 40k seems like some pretty dirty fuel, OR at least sub-optimal combustion?
That's a head scratcher.
I'd be interested to see what yours looks like myself lol

Click to expand...

The owner of that car drives it like a grandma - I keep telling him to beat on it more! It might be a good reason to delete the EGR for him. Right now it's bone stock.

The one with a dime sized opening was so underpowered it wasn't funny - like dangerously underpowered. I thought I was going to die driving it home in commuter traffic! Needed a MAF too so maybe it wasn't trying to make any boost anyway. That owner had just picked it up and rescued it from it's last owner.

As far as VW cleaning or replacing the intake on mine - I'm not sure. It only had a little over 100k when the timing belt broke. He showed me the receipts when I did the second replacement around 180k and I don't remember any mention (it's been a while). I know it had pistons and a head installed and was around a $5k bill.

I will definitely take pictures of mine I did the torch method on the last couple I cleaned but that one I mentioned was so clogged I couldn't get any enough airflow through it to keep it burning!