1991 Audi 90 Quattro 20V Idle/Power Loss

[NinetyQ]

I'm having a problem right now with two symptoms that started at the same time. When the engine is cold, it will start but only stay running if I keep my foot on the gas and keep the RPMs above 1k. Once the coolant temperature gauge rises to the second marking, and only when it reaches that same point each time, it will run on its own.

On its own, you'd think it would be the coolant temperature sensor or something like that. But the other problem that began at the same time as this one is a loss of high RPM power. Under normal circumstances, the engine pulls decently to 3500 RPM and then really surges in power above that, but since my problem began, there has been no higher rpm surge, and above 5000 RPM it simply runs out of power. It's to the point where it will rev higher, but as soon as you go into the next gear and the revs drop back down, there's actually a surge of power as if there's more horsepower lower down in the revs than in the upper power band.

So to sum up, these two problems began at the same time. The symptoms are that the engine will not idle on its own until warmed up and runs out of power between about 4 and 7k RPM (though this seems to vary slightly depending on the day, but it is never "normal").

I've also ordered a new high pressure hydraulic hose which will hopefully cure or at least help pinpoint my hydraulic issues. I currently have a lack of steering assist and the brake pedal is stiff on the first stop or two and loosens up suddenly.

[Ruffiano]

you have a vacuum leak. find it.

the brake problem sounds like a failing "bomb", you would need to swap a new one or recharge the old one. Generally the way to test is a couple of pumps on the brake pedal, see how quickly your "brake" light comes on.

[NinetyQ]

you have a vacuum leak. find it.

the brake problem sounds like a failing "bomb", you would need to swap a new one or recharge the old one. Generally the way to test is a couple of pumps on the brake pedal, see how quickly your "brake" light comes on.

Thanks for the help! I can't check into it more right now since the car is 120 miles away, but I did check to make sure the fuel pressure regulator had vacuum, and it seemed good. I'll look into it more thoroughly next time I'm home.

As for the brake bomb, would that affect the power steering?

[NinetyQ]

Also, the brake light often comes on and stays on when you start the car. And then occasionally while driving along, it will go off, but then almost always come back on as soon as you apply the brakes.

[NinetyQ]

Alright, I finally got around to checking the codes. I just bought a 12V LED from radioshack and used a scrap piece of wire for the ground, and it worked! I got five codes:

2232 - Air Mass Sensor
2212 - Throttle valve potentiometer
2342 - Oxygen Sensor
4343 - Carbon Canister Solenoid Valve, valve 1
4331 - Carbon Canister Solenoid Valve, valve 2

Those are the codes and their meaning according to 20V.org.

[NinetyQ]

I took stuff apart today and cleaned the MAF sensor, throttle body, and electrical connectors. Everything but the throttle body looked fine before I even began, and even the throttle body wasn't bad. Just needed some minor cleaning. No difference in the way it ran though when I put it back together.

With the codes I've already listed, and with the cleaning not making any differences, do you guys have any suggestions? I kind of hate to just start throwing more parts at it until it runs right.

To review, the car does not idle on its own before it is warmed up. If it's a warm day like it has been, sometimes the idle will seem like it levels off but it's never for more than a couple seconds before it starts to stumble and stall unless I intervene and give it some gas. The car also runs out of power at higher rpm. I haven't actually taken the car on a drive since I cleaned everything, but I'd strongly suspect that's still the case.

Thoughts?

[AudiCoupeGT]

Haven't worked on these cars before but...
have you checked the coolant temp sensor and O2 sensor? Perhaps checked the connection resistance values and check the state of the sensors. Also, if you haven't yet, check for vac leaks. They can definitely cause major running issues.

[NinetyQ]

Haven't worked on these cars before but...
have you checked the coolant temp sensor and O2 sensor? Perhaps checked the connection resistance values and check the state of the sensors. Also, if you haven't yet, check for vac leaks. They can definitely cause major running issues.

I agree, they can cause problems. However, the problems a vacuum leak would cause would disappear at higher rpms. Also, my problems (cold idle/high rpm power loss) showed up at the same time. And I didn't get codes for the coolant temp sensor, but if I can't figure it out with the stuff that I actually got a code for, then I'll check it.

[Ruffiano]

k the last two codes tell you your evap system has openings which means YOU HAVE VACUUM LEAKS. so get in there and start replacing vac hoses.

and YES the p/s pump gives power to the hydro brake system(the bomb) so those problems are most likely related. the brake light taht stays on is telling you your bomb isn't working properly, or your ebrake is on.

[NinetyQ]

My question was not whether the systems were interconnected; it was whether a bad bomb would affect the power steering.

Also, I never said I didn't have vacuum leaks, only that they are not my main issue. Whatever is causing the high rpm power loss is what I want to fix first, and that would not be a vacuum leak. I don't have money to just throw parts at it until it's fixed. As it is, and from what I have heard from others I've talked to, it sounds like the MAF sensor is likely the biggest problem. The other stuff needs fixed too, but for now, I'm trying to focus on what will make the biggest difference. My monthly costs exceed my monthly income right now, so I'm trying to do this as economically as possible.

[JGarrigan]

check the intake housing between the MAF and your throttle body. They tend to get cranks in them(usually on the bottom where you can't see without taking off) from people fighting with them when they change the air filter or simply are just taking them off, i've also seen the pipe that connects to the bottom of that same piece not in place properly. Goodluck!

[NinetyQ]

Well these definitely aren't the same. Is the new one actually supposed to be missing the connection next to the base of the wire? All the options on RockAuto show the same kind of thing, but it clearly doesn't exactly match the stock part.

Also, thanks guys for helping out! I checked the hose when I took everything off and didn't find any thing that looked like it could be leaky. Minor surface cracking, but nothing deep enough to go all the way through.

[NinetyQ]

Well this problem ended up being embarrassingly simple to fix: the #27 and 28 fuses were missing completely. I don't know how I overlooked it for so long. I just wanted to end this thread with a solution so others coming along looking for help can find it or at least know what ended up happening in my case.