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Discussion Starter · #1 ·
As stated in the title, I've fixed one problem after another on my vacuum system, and each time the car has felt like its HP has jumped by 15-20, with particular improvement in the mid-RPM range. But then, after a few days, it goes back to feeling...not impotent, but not vigorous like it had been right after the repair. Interestingly, the exhaust note also changes for the better at first, and then returns to normal.

So, since I'm obviously changing the airflow and air pressure characteristics by patching holes and replacing broken stuff, what does this increase in power followed by a return to prior performance say about my engine? Am I running too rich normally? Too lean? Are my air sensors (MAF, o2, who knows what else) malfunctioning? Or is this to be expected? At any rate, what can I do to keep that extra oomph the next time I fix something on my air intake?

For the record, my engine is an AEB.
 

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If you are resetting your codes or disconnecting the battery, it will do that until the ECU figures out something is wrong. After fixing all of my vacuum leaks I was still have the same problems. I discovered that I was given a bad MAF.
 

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Assuming that all the vacuum line are good, and the MAF is bad. Is there any chance of hearing the pssshhhh leaking noise? I am having the exactly problem as the orginal poster. I've no CEl, and used a VAGCOM to scanned with no code found.
 

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Where are you hearing the noise from. You can take a mechanics stethescope and put it on the hoses. You'll find a leak that way or at least pinpoint the area of the noise.
 

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Discussion Starter · #7 ·
Since more detail is needed:

- I've cleared the DTCs every few months, but it's never had any effect on the way the car has performed, mostly because only once were there any codes to begin with.

- I have only once disconnected the battery when working on my car (I prefer the "be careful" approach except when performing electrical work), and the car idled like shit for a couple of days. During the first test drive, the engine stalled a couple of times when coming to a stop. The next two days saw the engine revs drop to 500 for a split second before stabilizing at 800 when coming to a stop. Then, on the third day, it suddenly went away.

- Neither of the two things I mentioned above have any direct bearing on my question (though they may have a common cause), because I never disconnected the battery or reset the DTCs when repairing the vacuum system.

I have no idea what my fuel trims are. I don't own a VAG-COM yet, though I do plan to get one at some point. Ross-Tech says that both the serial-port and the USB-port versions of the cable have a built-in license hardlock; considering most computers (especially my old laptop) still have serial ports, will I really be losing anything if I buy the serial port cable?
 
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