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Discussion Starter · #1 ·
89K miles. ALH engine. Problem: reduced power.
VAG codes:
P1549 Boost Pressure Regulation Valve (N75) - Open or Short Circuit to Ground - Intermittent
P1441 EGR Valve (N18) - Open Circuit or Short to Ground - Intermittent
P1144 Mass Air Flow Sensor - Open or Short to Ground
P1252 Commencement of Injection Valve (N108) - Open of Short to Ground - Intermittent
P1550 Charge Pressure Control - Control Deviation - Intermittent

This is not limp mode behavior. The VAG behavior when accelerating and watching the MAF function is exactly what indicates that the MAF was bad (suggested air flow ~800 actual air flow will not go over 400). So I replaced the MAF. When I cleared all the codes with the VAG-tool they did not come back but the power did not come back and the air flow values did not change. I guess the approach is to clean/replace all the tubes and then it is clean the intake manifold. How do I proceed here?
 

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Discussion Starter · #3 ·
I installed a new intake manifold, cleaned the very dirty EGR valve and replaced half or more of the tubing. The car ('99 TDI Beetle) then ran fine. I was able to get the air flow mass reading from the VAGCOM software up to 620 at around 3000 rpm. Before the work it wouldn't pass 475. There was only one code error code now, a glow plug error (high-resistance/bad connection). 4 or 5 test runs of a few miles were comleted with only the glow-plug error. I took the car to the emission station 20 miles from me and it passed the test. Starting the car to drive home, the code light came on again and upon arriving home I used the VAGCOM and the P1550 error was back along with the glow plug error. When I went to repeat the 3000rpm road test, air flow mass would go no higher than 525...better but the code was there. Does this mean I need to have cleaned the head? The ports were not very dirty and I had cleaned crudely the outer inch or so and vacuumed up the junk. Aside from re-checking my tubing connections, which I redid and checked carefully already, what can I do? I want to sell the car and will need to get rid of the 2 codes. Drivability is fine. There doesn't seem to be a whole lot of turbo boost, but acceleration is good by my test. I checked for uniform 0.7 ohm resistance on the glow plugs and that was good, so for this I just have to dig into the wiring a little. I suppose the N18/N75 valves could be bad, though they did not seem to be factors in the initial diagnosis. What now?
 

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Tray swapping the N75 and N18 valves. Your first post indicated an issue with the N75 (not sure why that was overlooked).

The MAF issues "could" be related to the turbo issue (N75) and you're in some sort of limp mode. In general, with a good MAF you should be able to run your RPMs to full (in neutral/park); if not, then the MAF is suspect (unless one gets a quality MAF there's a good chance of getting a crappy one- and, well, every manufacturer is going to put out a bad part here or there, so one cannot assume a new part is NOT bad).

I'd also check your turbo actuator to see if it's working properly.
 
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