I replaced the supercharger and added a 15% pulley on my 2004 Mini S this weekend. The idle is now going up to 1500 rpm and then drops to normal idle and repeats. I am getting codes P1109 and P1242 which Bentley says is: manifold pressure too high in deceleration and secondary upstream manifold air pressure sensor too high in deceleration. I have reset the ECU and the codes keep returning. What should I look for? Thanks for any help!!
Ed Burberry

 

By-pass valve may be sticking or is stuck. Dont know if you messed with anything on that end, but might be worth the gander. Do you hear any vacuum leaks maybe ?

 

Sound to me like there is a leak somewhere or a sensor wasn't reconnected.

 

sounds like a sensor to me. Did the car ever throw you into limp mode?

 

No limp mode, it was one of the intercooler boots.

 

i just started my car with the intercooler removed. it made awful sounds so i turned it off right away. i replaced everything the way it should be and now its not idling properly. its very sputtery and low toned and bouncing up and down around 1k rpms. any ideas?

 

Check the rubber boots on the intercooler, they may have slipped when you tighten them causing an air leak. Hope this helps
Ed

 

Yep and you'll see soon enough if one of the intercooler boot isn't properly seated, the manifold will turn bright red

 

just took down and rebuilt everything, double checking as i went. everything is def sealed now and having the same problem. the engine light came on, blinked a few times, then stayed on. i dont have a scanner so i dont know the codes.

 

yes! just cleared the codes and its back to normal. dont know how or why that fixed it, but it did. what a relief!

 

Yup, either you corrected a problem that wasn't obvious or the ECU tried some radical compensation for the "start w/o I/C" & just took a little to go back to normal.

 

Did you undo the battery during install?

 

no i did not.

 

Try that. Undo battery and wait 30 minutes. Also I found that if I mix fuel grade I.e. 91 and 93 I get idle bounce. Try sticking to one or the other should smooth it out a bit more of the batter unplug doesn't work

Edit: guess you fixed it