S5 Turbo w/RB REV-II exhaust system, HKS intake and S-AFC II (currently disabled). Car professionally dyno-tuned previously and ran great prior to a recent track event.

Since the track event, I've been wrestling with a rough idle, actually engine shaking back and forth, with engine fully warmed up. Idle actually holds steady at 750-800 rpm. Checked all the suspected sources of the problem including TPS (new after previous CEL in May), swapped coil packs, tightened clamps on all intake piping, disabled S-AFC II to remove it from the equation, examined vac and air hoses for leaks but nothing obvious.

Sprayed engine starting fluid around the engine compartment to search for a vac or air leak. When spraying around the turbocharger, the engine smooths out nicely. Same results whether sprayed around the compressor air intake piping attachment point or the side of the turbo away from the piping. Clamps on all air intake piping have been tightened. Vac line to wastgate actuator replaced and zip tied.

Obviously, I will need to remove piping and vac lines, etc. to examine for leaks, but would welcome any other suggestions as to what to look for. I'm a little new to the turbo world, so all help is appreciated.

Larry

 

What about the metal hardline for the wastegate actuator? Is it loose or pressed in there tightly?

 

Do a damn leak down test. Go to home depot, buy a 2" cap, and put a compressor male end into it. Take off the tid, and put it on the inlet, use the regulator on the compressor and set at 10 psi. You should hear/feel the leak out. If not 15 psi.

 

^^ It would need to be a 3" cap to fit in the TID to AFM connection.

 

RR88: Good question. I'll check closely when I get the piping removed. Appreciate the idea.

2slow/1SWEET7: I'll give it a try. Are you talking about a plastic or rubber cap? Thanks.

 

I used a plastic 3" cap that has a little square on top then drilled a hole and inserted a tire valve stem.

 

yes the boost leak tester tools are very helpful. I have solved innumerable little leaks in my intake and turbo system using that method.

 

The turbo inlet is pretty small.. But 3" would work with a clamp.

 

The turbo inlet is about 2.25", 60mm if I remember correctly, but you just need to get a 3" to 2.25" reducer if you want to test from the turbo. I tested from the TID so I didn't need the reducer.

 

2slow4stock, you ARE da man! I pressurized the intake piping and immediately heard air rushing around in the area of the intercooler piping. The problem turned out to be a split in the short hose that connects the BAC valve to the OEM intercooler piping (see the attached image). Took awhile to find the leak even with the air flowing since the split was at the back of the pipe and not visible. Finally isolated the leak by feel, fixed it and the engine now idles as smooth as it has ever been and the boost level that had dropped off a couple of psi is back to "normal".

One caution to those doing the same sort of test procedure. After replacing the split hose and reinstalling all the associated piping, I pressurized the system again to make sure there were no more leaks. After about 5 seconds, the 3" plug I had rigged up for the TID blew out with some force, even at 10-15 psi. So stand out of the way if you do this with an intake system that may actually be sealed.

So many thanks to 2slow4stock, and the other posters, for your assist!

 

No problem. That's why I test on the turbo itself then the tid.