I had a new issue pop up on my R53 this week. When I was coming home from work the other day, I noticed my idle was rougher than usual. When I got home, I shut it off and restarted it, and got a misfire so bad it almost stalled out, as well as a bunch of codes pointing to a misfire on cylinder 1, rich mixture, the throttle position sensors. Today I took apart the throttle side of the intake system and tested the sensors, no issues there. When I put it back together, cleared the codes and restarted it, the only code that came back was P1498. I took off the intercooler and resituated the boots a little, but that didn't help anything. It sounds like it's about to misfire and has a faint gas smell if I hold the throttle around 2000, and also makes a light jingle or metal rattle sound when slowly going up to this rpm. What's making me nervous is that there's a lot more vibration than usual, and it sounds like something is roaring somewhere (almost like a wheel bearing would).

While I was digging around more, I did find that the top of the fuel vapor purge canister next to the belt tensioner was bent and cracked where the top vacuum line runs out. I have a new one on the way, along with a new PCV valve and hose. I replaced the throttle body gasket and supercharger inlet gasket when I rebuilt a few years ago, so I'd assume those are fine still. Is there anything else I should look at while I'm at it?

 

Misfire on Cyl 1 - I had that. Found a thread on this site - the cat is partly press fit. As they get old, the press fit comes apart. This causes random misfire codes. I had it welded - as per the thread. Misfire gone

 

Ah, I didn't realize an exhaust leak could cause misfire. This car's cat was removed by the previous owner and I haven't replaced it. Could that add to the issue?

 

no codes?

 

I seem to have fixed most of the issue. The codes for the misfire, rich mixture, and throttle position all went away after I took off and put back the throttle body, but then I still had a decent misfire that didn't bring up any new codes. The 1498 and 1477 codes were tied to three vacuum leaks. The fuel vapor purge solenoid was cracked at the top where the vacuum line running to the throttle body connects. Also, that splitoff nipple a few inches from the vapor solenoid was broken off. I went ahead and swapped out a few maintenance items while I had a loaner car: intercooler ducts, fuel filter, timing chain tensioner.

Starting it up got me a little nervous. It took a good 4 restarts and 10 or so minutes of idling in the garage before the misfire went away. Cleared all the codes once I got it to level out and nothing's come back after test driving it for 20 minutes (with a few pulls up to around 4500rpm). Only issue I've noticed now is that when I let off the throttle, it struggles to hold idle for the first second, then bounces back up. It's more noticeable if I'm low rpm. The engine doesn't stall, but drops to around 400rpm before I hear it turning over again. Other than that, it sounds and pulls better than it has in a long time (possible since I've owned it).

 

good work. its really hard to say without codes. I might have said this before but it sounds like sensor issues. map and tmap. but that a guess