The Project Pad

Hi Guys,
I guess I should start off by introducing myself a bit. I've been a lurker on a lot of forums. But I've been dedicated to this drivetrain since about 2009 when I got my 91 avant. I liked it so much I bought another, and then a Quattro with the same engine (albeit with some RS2 upgrades).

Anyways, I want to get more active on these forums, but since I'm in the hate part of my love/hate relationship with this car, I'm reluctant to be active. Maybe this post will help...

I have had this idle issue for a while now. Its about the only code I have, and its starting to wear me thin. Maybe there is a way to set the idle on motronic that I am not aware of, maybe its something really simple and stupid, but here it is.

Here is the code:
• 2231 (Blink Fault Code), 00533 VAG1551/2 Fault Code Number
Idle Speed Control Valve (N71)
Idle speed adaptation maximum limit exceeded or Minimum adaptation limit not reached
Sticky or binding ISV, Mass Air Flow Meter (G70) offset, additional air introduced between G70 and N71
Symptom: Idle speed too low, or too high, Add air leak.

Here is what I know about my particular situation.
-The car never idles at 700, its always at about 1000
-The CEL only comes on when intake temps are below freezing, I can sit in a garage all day and it will not come on, but the idle is still high.
-When its on, and the car is fully warmed up, I can shut the light off by loading the engine (holding the power window switches or turning on the lights).Once it hits about 700 rpm, the light goes off.
-What I think is happening is that the ISV is trying really hard to idle properly, but is getting a reading that there is too much or too little air. As it reaches its limit, the light turns on. Once I load the engine however, the isv has to work less, and it falls within range.
- When the CEL is off, the ISV acts exactly as it should, let off the trottle, it drops to 1200, then lowers itself down to idle. However, it only lowers to about 1000 rpm.
-Its driving me crazy that I can't get the idle to 700 even when the CEL is off.
-When the CEL is on, if I slowly apply throttle, from about 1200-2000 the RPMS surge very consistently, once I get past 2k, the rpms stop bouncing.
-I can keep the CEL off by keeping over 2k rpm at a stop light
-When the CEL is on, it runs like crap until about 2k, then its ok, but with less power.
-The thing takes longer to crank than it should too... I can't understand if this is related. Cold mornings after the car sits overnight, fires instantly. Any other time, it takes a lot of cranks.


Here is where I stand with parts.
-This is a fully built as new 3b with about 1000 miles on it. All sensors are new except for the MAF, TPS, and Intake air temp sensor. All new sensors are VW/Audi items. The wiring all checks out, i'll be giving the ground wires a cleaning today.
-The coil is old, but I'm not really getting any misfires
-The 3b before this had a similar issue. The problem could be in the wiring harness, but I have no idea where to start. All the continuity checks pass.
-I tested the MAF, resistance values are correct, and so are all the solder joints. I also swapped the MAF, same symptoms.
-I cracked open the TPS, and re-did all the solder joints. Nothing looked bad, and the potentiometer tested out fine.
-There just can't be any boost leaks. Everything is tight, no hissing, the boost gauge hits 1.8/1.9 bar (chipped), and drops to .3/.2 when you cut the throttle. Maybe im missing something and don't know how to check for leaks?
-The ISV is new, the wiring was fixed going to it.
-The PCV was put in backwards, i put a new one in, the right way.

Pic 4 Clicks

I have seen these kind of symptoms many times.

I am 90% sure that you DO have a vacuum leak. These leaks are very sneaky. If it was an AAN, I would start with checking the little rubber T piece under the IM that holds the PCV (one way valve). Those are prone to cracking in the joins and cause havoc with idle.

Another is the ISV itself. It could be leaking out the back. Where the plastic plate is with the connector. Once they get older, they can leak around this plate between the steel body and plate. BTDT. Get it sealed up with some JB Weld. Can't hurt.

Try to do another boost leak test where you test the whole system. You put the plug with nipple into the hose from the MAF, take out the PRV line (pancake valve) from the MAF to turbo hose, plug that hole. Then run the pressure up to about 15psi, SLOWLY! Close the air supply and listen. It will drop down slowly. From 15psi to 0 in about 10seconds.

If not the above, check out the coolant temp sensor.

Nice car, does the side of the block crankcase hose look ok the entire way around? Do they feel like they are they clogged on the inside if intact?

I would check again to see if those are the only codes you're getting, also check the wire connections by the ecu and especially through the firewall ... maybe even pull out the ecu connector a decent clean and plug it back in.