Car is an S5 NA GXL, 5 speed.

Here is the problem. When I connect the body harness in the ECU and put the key to ignition, the headlights pop-up. If the revs go lower than 800 rpm the lights go down but when I hit the gas they pop up again...Also, as soon as the secondary injectors come on, the car ''burns" the ecu and after that it wont go past +/-3800rpms, just like as if the pressure sensor was shot. We noticed this when we swapped an ECU form another S5. The car ran great for 2 seconds above 3800rpms and then started doing the same problem. When we put back the ecu in the other S5 it wouldn't go past 3800rpms either.

I dont know what was done to the car beforehand also. I got it that way.

Any ideas?

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hmm. Does the Check engine light come on? Does the ECU actually burn up? What is the current postion of you headlight switch, and how many miles are on the car?
I'm leaning towards you lost your OMP, when the electronic S5 one goes bad, alot of times it will burn out the ECU as well, and it doesn't throw a code right away(Check the OMP per the FSM, because if it is bad, it can keep burning up ECU's, and that Bad ECU will sometimes burn up a new OMP).

But I don't know Where the funky headlights would fall into that.
Check the voltage coming off you alternator and see how much it changes over the wholke process.

 

I had already tried with another OMP and no change. And its not limp mode either. Its really exactly like as if the pressure sensor was shot. Could it be the relays where the harnesses meet up?

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so you have no history on the car? no clue what has been done to the electricals prior to you owning it?

is it a swap? sounds like maybe some of the pins on the harness are in the wrong spot... or there is a short somewhere.

worst case scenario would be having to swap the harnesses to known good ones.