Intermittent severe loss of power A4 B5 1.8 normally aspirated Avant.

[rod955i]

Hoping someone can help with a problem I have with my year 2000 1.8 normally aspirated Audi A4. Severe loss of power occurs intermittently on any short journey, it is as if there is insufficient fuel or air getting into the engine.
I have connected VCDS up and there are no fault codes.
I had replaced the Intake Manifold flap a few weeks before the power issue occurred as that was broken, vcds output tests confirm good operation of the replacement. At lease I assume they do as the actuator moves during the test and there are no fault codes thrown.
I have replaced the fuel filter.
I have replaced the MAF with a new Bosch unit - same as Audi use but not badged.
I have replaced the spark plugs.

When the issue is particularly bad foot to the floor throttle will result in a strangled response from the engine and revs wont rise above 2000 rpm.

Stopping the engine by turning the ignition off and then starting it again once or multiple times temporarily clears the issue, otherwise it sometimes clears on it own only to re-appear at a random interval later.

Car is due to go to garage on 5th May and have asked for smoke test to test vacuum hoses and hopefully some diagnostic steer on what it might be.

Any ideas anyone?

Thanks

Rod

[Crasher]

I would fit a genuine VAG dealer supplied AMM and go from there. I have never known an ADR engine to go limpy, we've got one the same as a customer battering ram, sorry loan car, and it's bloody strong-needs to be!

[rod955i]

Thanks Crasher - this is the second MAF unit I have fitted, first one was an Ebay £29 Chinese knock off - no reason to suspect that the genuine Bosch item is bad. As I said this unit is exactly what Audi supply but with an Audi sticker. Looking around the web and others with the wont rev symptoms candidates are vacuum leak or possible lambda oxygen sensor but as there are no error codes thrown not sure lambda would be likely. Engine is APT code.

[rod955i]

Sorry Crasher just realized you were recommending replacing the AMM lambda sensor not questioning the veracity of the MAF - will look at replacing the AMM doing that.

[Crasher]

No, the AMM, MAF (Mass Air Flow) is a nasty Americanism for an Air Mass Meter, both myself and thousands of other people have had problems with non genuine AMM's-even Bosch, well labeled Bosch anyway. With no codes and no having anyone with experience on them to actually work on the car there is not a lot else to suggest, you have done the most common one, the manifold flap. We did have problems with the coil pack unit on ours, it fell to bits and a new one was simply daft money so I bought a pattern one but that also fell to bits so I had to rebuild it. You have made sure this works haven't you?

[rod955i]

OK thanks Crasher that makes sense.
I will go ahead and replace the front Lambda sensor as the symptoms kind of add up (there is also a history of this car destroying CATS which the garage thought was caused by the inlet manifold flap failure). The engine has low revs with no misfire and overheats suggesting very lean mixture, this happened when the fault occurred climbing a particularly steep hill. If that does not fix it I will get the garage to do a vacuum smoke test and if that comes up clean will ask them to replace the MAF with genuine VAG item. Will post back whatever hopefully fixes it. As the car is not worth anything to anyone else, a few hundred pounds at most and if none of the above work, I will call time on it and it can go to the great re-cycler in the sky.

The Inlet manifold flap operates when doing the output tests and no codes are thrown - it moves back and forwards a couple of times then goes to full extension for the rest of the test. Not sure if this is the correct behaviour or not but seems to be as others have said it should do something like that.

thanks again.

Rod

[Crasher]

I have had non genuine lambda sensors, even Bosch, act up on this engine but they do leave a code when causing trouble. The problem is down to the current drain monitoring for the heater.