Ranson

Hello fellow Audi Lovers. I have 2 A4s and I think they are great cars. A B6 with 230K miles and a B5 with 137K. Late last year, the B5 (my Son's Car) started using oil and I couldn't figure out why. Cut to many months later, the engine seized due to lack of oil. No idiot light either. The info screen had also recently stopped displaying critical status. I sourced an engine from a 1999 Passat. Same engine codes (AEB Head with 058 Block), same transmission type. I installed the used engine. That is a story in itself but in short I replaced just about everything one should replace as I had planned to keep this car for myself. Oil pan was removed to ensure no sludge and oil pickup screen was clear. All new sensors, new injector seals, new PCV system hoses by 034, all new vaccum hoses and check valves, new clutch, new cam chain tensioner and new timing belt kit. There are other parts that are too mundane and too numerous to list. The car started up almost right away upon reassembly and I notice a rough sounding idle. No big deal, I'll just inspect the hoses and find some air leak that needs attention. There were a few places that were remedied for the air leaks, however, I have not been able to find the main source of the problem. The car throws a code of P0300 (Random misfire) then eventually throws a code for the individual cylinders. There are no other codes that would indicate a source for the misfires or air leak. The car runs fine once the RPM is up and accelerating. It does not misfire while driving on the highway, it only misfires during idle. It is a lean condition (usually due to unmetered air getting into the intake) that causes the engine management system to add more fuel to compensate. The lean condition isn't noticed by the computer once RPMs are above 1500. I took it to three reputable different mechanics. All my hoses are correct and no air leaks detected. The Audi mechanic smoke tested the vaccuum system, pressure tested the air intake sysyem and tested fuel pressure. They tested the compression and were surprised at the eveness and high compression of all cylinders and asked many questions I could not answer regarding the history of the engine. We could see the fuel maps and how the engine was detecting excess air. The Audi mechanic suspected the engine or the head had been previously reworked. Of course, they wanted to continue to work on my car at a rate of $135 per hour. It doesn't take a genius to figure out a 17 year old car isn't going to be worth that kind of labor rate for very long. I left the dealership disgusted and trying to decide whether to sell it or continue to drive it as is and let it be a source of frustration as I continue to throw money at it. One important note. The original engine did not have an idle problem, just a oil usage problem due to the PCV system hoses being cracked and broken. I believe the idle problem came with the used engine. Assuming the idle problem is internal to the engine, what could cause it internally? Could the best Audi had to offer have simply missed an external air leak? I plan to check ground continuity on all grounds. I have not swapped the turbo over from the original engine. The used engine came with Intake including Throttle body. The exhaust was also attached with the turbo. I chose to leave the exhaust side in tact as I was concerned the lack of oil may have compromised the original turbo. However, I have completely reworked the intake side to include the original fuel rail and intake maniflod.

I'm desperate to find the source of this idle problem. I've sprayed several cans of carb cleaner on all hose and junction points looking for a change in idle. I've pinched hoses, disconnected the MAF. All the usual stuff to locate air leaks.