Its a mostly stock S7 and everything is fine unless the engine idles for approx 4 seconds or more then it appears to go into limp mode, although I'm not so sure it is limp mode as the ECU will still allow 2 or 3psi of boost pressure instead of the usual 0hg. The problem is just like limp mode e.g map activated, not rpm activated, and the usual popping/backfiring/banging.

If I turn off the engine and start it again it runs fine until it idles for 4 seconds or so, so it must be something that resets by switching off the engine. If I keep revving or blipping the throttle as soon as I start the engine it revs and drives fine, but as soon as I let it idle for 4 sec or so it goes back into the same mode. Idle quality and off-boost response doesn't change. There are no error codes present and I've changed the map/boost sensor. This happens like clockwork and is always at 2-3psi so it must be electrical.

Airpump, EGR and cat have been removed. Engine has a mild port.

I've noticed in the past that when FD's drop back to idle after free-revving there is a solenoid somewhere in the engine bay that clicks a few seconds after idle speed is reached. Does anyone know what it does?

Thanks!

 

Are you using the stock ECU? If so, have you check for the ECU storing any codes?

 

Yes the ECU is stock and no there are no codes present. I wish there were so knew where to start looking.

 

Are you judging that on the fact that you don't see a check engine light, or you actually checked for codes and none came up?

 

I've checked for codes several times and none are present. I can induce codes by unplugging sensors.

 

if you have access to another ecu, i would try that.

 

I thought that the stock ECU couldnt handle much, i think running without a cat would definitely cause problems on stock ECU. Especially if your running some other mods and the car is JDM without a pre-cat.

 

SOLVED

As the car is JDM there is no check engine light so I tried checking for error codes with the engine running and bingo, code 27 OMP. I plugged in another OMP and no more limp mode. This is the first time I've seen an error code that wasn't stored in the ECU. As soon as the car was switched off, then on again (without starting), there was no code. This code was only present with the engine running.

 

Good deal. That's what I was getting at when I asked if you were seeing a check engine light or not. Glad is all fixed. Enjoy the car!