Hello all,
I have been trying to diagnose an intermittent high idle problem in my TII that cropped up after I blew a heater hose and overheated a few weeks ago. After replacing all the hoses and flushing/replacing the old coolant I am plagued by an intermittent high idle. Upon startup the car runs through its 2800rpm 2200rpm 1600 cycle, but sometimes it sticks at 1600 or 1400 and wont go any lower. Then randomly it will go to normal 850-900 idle, then sometimes 1100. Ive also noticed that the car is not as powerful and not making as much boost when the idle goes screwy. When the idle is normal, I get normal boost and power. The vacuum gauge sits at -200mmHg when at (higher than normal) idle (I believe this is normal, but Im a noob at turbo's, this is my first one) and then will approach zero around 4000rpms, then goes to about +200mmHg, at 7000RPMs. When the idle is normal (850-900) it will start to boost at about 2000RPMs and generate +300mmHg by 5000RPMs.

I have checked for vacuum leaks by spraying starting fluid on all the vacuum lines with no change in engine sound. Ive replaced the spark plugs, replaced the airfilter with a K&N, and tried burping the coolant system 3 times, so I dont think there is any air in the thermowax system. I tried adjusting the idle at the BAC and the lowest it will go is 1400RPMs, then when the idle goes back to normal the thing drops to 600rpm and I have to turn it back up. Im at a loss as to what to do next, any advice would be greatly appreciated. I really dont want to have to replace the BAC, as those are like 500-600 bucks.

 

i would look for a vac leak. adjust tps, bac and (rich/lean adjustment -s4 only)

also check the adjustment of the cold startup cam,