1Z 00575: Low Intake Manifold Pressure - Troubleshooting

Dear DIY community,

Another one searching for the causes of a mysterious "00575"...

In my case, the actual intake manifold pressure is too low; it's consistently several hundred millibars below the target pressure under load (unfortunately, I don't have a web space where I can upload the log file for you to download).
The intake manifold appears to be sealing properly, with no oil leaks.
"I can consistently reproduce the error (00575) described here when driving uphill on the highway under heavy load. Around 140 km/h going uphill, the power drops off. My assumption is that the difference between the actual and target intake manifold pressure becomes too large (instead of 1850 mbar, only about 1330 mbar are achieved), causing the engine control unit to cut fuel supply."

I can think of two possible causes: 1. The wastegate is stuck in a semi-open position. 2. The pressure sensor is providing incorrect readings. Since the car accelerates normally and responds as usual, I'd like to check the pressure sensor. I have a Passat from 06/95 with a 1Z engine. I assume this is the engine version where the pressure sensor is integrated into the engine control unit (ECU), and there's a hose running from the ECU to the intake manifold or intercooler. Embarrassingly, I haven't been able to locate either the engine ECU or the thin hose that should be connected somewhere to the intake manifold or intercooler. I'd like to check if this hose is dirty or misplaced. Could you tell me where I can find the hose and the engine control unit? (Yes, it's embarrassing...)

Regarding hoses: Another thin hose, which is NOT for the EGR valve, also branches off from the vacuum pump and then goes through a solenoid valve located above the intake manifold in the left fender, towards the bundle of cables/hoses at the top of the rear firewall of the engine compartment. It's a white, thin plastic hose. Does anyone know what it's used for? It seems like some other component still needs vacuum pressure.

The visual and functional inspection of the pressure sensor/wastegate lever is still pending. I will, of course, report the results.

Here's another question for the specialists: In my log, the duty cycle of the pressure control valve in idle is approximately 90%, and under load it drops to 40%. I think that if the target and actual pressures are close together, the ECU opens the wastegate via the control valve (90% duty cycle -> valve closed, no atmospheric pressure, gate opens earlier). In a loaded condition, when the target and actual pressures continue to diverge, the ECU tries to keep the wastegate closed in order to increase the actual pressure (40% duty cycle -> valve open, atmospheric pressure is mixed with the turbocharger pressure, the gate remains closed at higher boost pressure). Am I understanding this correctly? Where are the 1Z gurus ?

Thank you.
Greetings from Salzburg.
Michael.

Hello,

Here's the resolution of the story, under the motto:
Sh... engine cover or why we didn't need diagnostic programs back then...

In the wiring diagrams in the appendix of "How it's done," the location of the engine control unit (ECU) is indicated as "water reservoir on the right." This means "remove the plastic cover, which I had already fiddled with before, but I hadn't wanted to just randomly poke around there yet." Underneath this cover are the pollen filter and, lo and behold, the ECU with the medium-thickness fabric hose for the intake manifold pressure sensor. I traced the hose, which disappears under that ridiculous engine cover. Reaching underneath, I immediately felt it: The hose is torn at the nipple and kinked. So, it's indeed the pressure sensor/hose that's causing the problem, just as I suspected...
A mechanic friend of mine once said, "What's the point of the cover? It just blocks the view of the engine." He was right; without the cover, I would have immediately seen the cracked hose. And that was it. Now, according to VAGCOM, the boost pressure is correct, and the turbocharger boost control starts regulating at 1900 mbar.
And the moral of the story: What are engine covers for? Well, I now know quite a bit about VAGCom thanks to this, and I finally know where my engine control unit (ECU) is located...

It might be that this case is trivial for seasoned mechanics, but I think the example might still be helpful to some people.

Greetings.
Michael.

miguelito wrote:

It might be that this case is trivial for seasoned mechanics, but I think the example might still be helpful to some people.

Nice that you're sharing the solution with us.

Although the matter itself is actually quite trivial, sometimes you can't think of something as stupid as life throws obstacles (or hindrances) in your way. Therefore, it's okay for me .

Ah.

So, you're driving a Passat ?

Because the cover on the 1Z in the Golf 3 is so small that you can see everything .
Only the 1Z Passat had the large cover like the AFN engine.

Okay, please provide the German text you would like me to translate into English. I will only provide the translation.

Hi Ulf,

Okay, as I said, I wanted to carefully check all the points described in the numerous posts of this really good forum before asking any questions. But even though I've enjoyed working on cars for a long time, I was temporarily overwhelmed by locating the intake manifold pressure sensor connection/ECU. It's just another example of how you can use VAGCom to narrow down the cause of the problem.

"@dieselmartin - I used to have a TD III, and the connection for the intake manifold pressure (which was directly connected to the wastegate actuator on the TD) was located in roughly the same place (at the bend of the intake pipe just before it enters the intake manifold). When I had the cover off, I immediately remembered this picture, and I could have kicked myself. In that case, I would have preferred a smaller cover as well..."

Nevertheless: Passat forever!!

Best regards.
Michael.