some running problems and MAF sensor 7A

[djpeck]

Drive it, it needs to learn.

Okk, lets see what happen using it, thanks!

[newsh]

Does this car have an idle switch on the throttle body?
If so, maybe it’s not closing.

[djpeck]

Does this car have an idle switch on the throttle body?
If so, maybe it’s not closing.

Yes, I checked it and it is working correctly.

I used the car during this weeks and it works without changes. It is still increassing revs etc.

I would like to know if it is possible to swap ISV valve from old one to later one

• Early 1990 cars (CQ VIN <= 13610) have the Hitachi unit shown on the left -- Audi P/N 034 133 455 A
• Later 1990 cars (CQ VIN > 13610) and all 1991 cars have the Bosch unit shown on the right -- Audi P/N 034 133 455 B

A later one is easier to find it. So I would like to try it.

[Lago Blue]

Although when serviceable the two ISV types would both likely respond equally to signal, I don't think they share the same hose or mounting arrangement.

Another way to discern whether there is a vacuum leak somewhere, is to temporarily attach a vacuum gauge (such as a simple MityVac) to the I/M for starters, to read the inches of water column and run the engine till it is warmed up and your issue appears.

It might be that there is a vac leak that wasn't revealed by the smoke test, such as CCV hose from crankcase to the I/M, the oil fill cap and/or dipstick seal(s). or maybe the 3rd fuel line (the vent line) back to the tank or the gas fill cap seal? Edit: Almost forgot, the hose back to the diff lock and the vac reservoir there too.

[djpeck]

Although when serviceable the two ISV types would both likely respond equally to signal, I don't think they share the same hose or mounting arrangement.

Another way to discern whether there is a vacuum leak somewhere, is to temporarily attach a vacuum gauge (such as a simple MityVac) to the I/M for starters, to read the inches of water column and run the engine till it is warmed up and your issue appears.

It might be that there is a vac leak that wasn't revealed by the smoke test, such as CCV hose from crankcase to the I/M, the oil fill cap and/or dipstick seal(s). or maybe the 3rd fuel line (the vent line) back to the tank or the gas fill cap seal? Edit: Almost forgot, the hose back to the diff lock and the vac reservoir there too.

Hello, I don´t think ISV mounting could be a problem. My doubt is if it has the same electric values.

Regarding Vacuum leaks, yes... Maybe I have to check again...

Maybe the problem comes from the I/M or collector assambly, and leak appear whith metal dilation...
Or maybe it could be the ecu, or any sensor that goes out of values whith hit....


It is a shame that I couldn´t connect VAGCOM in this early 7As...
Maybe is eassier to swap ECU to 4 connector

[Bowie69]

One is a hitachi valve, and one Bosch, so likely very very different. Most other bosch valves seem to work for me, when I tried it. Volvo is a possible source, I think?

[Lago Blue]

I wouldn't fret over not being able to do Vagcom if as you say there are no blink codes to pull (i.e.: you received a 4444 code (meaning no faults stored) on your code pull, correct?). There are certainly instances when there is something amiss that is beneath the fault detection threshold, and the path forward is simply traditional trouble-shooting, not buying and replacing components on just suspicion. A DMM and a vac pump and gauge are your friends here.

With a simple hand-operated Mityvac tool, one can apply vacuum to the various branches of the vac. system individually to prove they are sealed to negative pressure (unlike what a smoke-test might reveal), and they can also be left under vacuum say overnight, to prove they do not leak down over time. Audi famously used often short lengths of a fabric-covered rubber hose for a good deal of the small bore vac system connectors (for the various hard plastic vac lines throughout the vehicle) which will all now be leaking vac. It takes about 3m of good BMW stiff synthetic thick-wall vac hose to replace it all.

That your idle issue does not appear until after warm-up may suggest that the issue is not the ICV, but is of a magnitude that the ICV simply cannot respond sufficiently to cancel it out. For instance, it may be that the fuel tank vent is not connected to the I/M; until after warm-up. If that vent line (or any other break in that system) where broken upstream of the vent solenoid valve, will then after warm-up you may have a switched on vac leak.

[Mikes2]

Have you verified the fuel pressure is correct or have you tried a different fuel pressure regulator ?

[Obli]

On my 90 20v, I found two splits in the intake hose. I only saw the second split when I removed the hose.

I also found a Y piece connector (from inlet manifold to charcoal canister cut out valve) with a leak. As my car isn't a quattro and doesn't have a vac connection to diff, the Y piece was capped off but the plastic cap had deteriorated and had a hole in it. From your image, it looks OK (no Y piece on yours but a direct connection).