CEL Flickering
 

Hi guys,

So over the weekend I took my S5 NA for a cruise. When I started the car and left my driveway I noticed that the CEL would flicker as I went through the gears (noticeably over 3k rpm). If I kept the throttle steady it wouldn't flicker anymore but as soon as I accelerated the CEL would flicker. Please note the CEL light would never stay on permanently ever. After about 10min the flickering would go away and I could accelerate through the rev range without the CEL flickering. This is a new issue. That last thing I did was installed HIDs to the FC with appropriate relays but they are wired up directly to the battery. I'm thinking maybe Sparkplugs or O2 Sensor (about 30k+ miles on it) Any input would be appreciated.

Best place to start would be by pulling the trouble codes. Here's a link that explains how to pull codes: 89-91 CPU Trouble Codes

So I ran the codes and got 13, 30, and 33. From the details of the codes I don't understand why the flickering CEL would go away after a few minutes of driving.

13 - Pressure Sensor (Intake Manifold Pressure) = Fixed at 29.9 inHg
30 - Solenoid, Relief Valve
33 - Solenoid, Port Air Valve

i would reset those, and see if it comes back. i might also look at the pressure sensor connector, make sure its clean and plugged in

my friends FD would overboost, and when it hit boost higher than what the pressure sensor would read, the CEL would come on. (it would boost ~20psi on the first turbo, pressure sensor only reads to 17 or so)

I would assume the solenoids are triggering because I'm doing the VDI air pump mod since I deleted the smog pump on my S5 NA Motor. Where is the pressure sensor connector?

The MAP sensor is located on the front side of the passenger shock tower in the engine bay. It is a 4 prong connector. This sensor has a vacuum line running to the intake manifold. Some have a restrictor pellet in that vacuum line.

Edit: I would disconnect the solenoids as well, remove them, clean them and their contacts and put them back in just to try and eliminate them from the equation. The FSM has tips on testing all these components and their operation. I don't think the ECU has any way of "sensing" that you did an air pump mod. It just runs the solenoids regardless of whether there's air to redirect.