Hello,

These past couple months have been a real headache on my R53. Coming home from work one day, it started misfiring while idling as I pulled into my driveway. Right away I checked codes, and got P0301, P0172, P0222, P0123, P1477, P1498, and P0420. I previously had P1477 and P1498 from an unfound vacuum leak. So I borrowed a car for a week or two and worked through my list of maintenance items. I replaced: spark plugs, air filter, fuel filter, broken vacuum lines, intake gaskets, front MAP sensor, timing chain tensioner, intercooler boots, and the rubber intake tube running from the airbox to the throttle body. This got rid of most of the codes, but I still had that rough chugging idle on cold start. Took it for a test drive after it levelled out, and got the following codes: P0171, P1498, and P1477.

One day last week I did a fuel pressure test to confirm the fuel rail is holding pressure - all is well there. When I started it back up for a test drive, all the codes and lights were gone. I had the battery unplugged for half the day while I did that, so I'm assuming that's why. Runs better, still chugs a little on startup, but not terrible and evens out after about 10 seconds. Now today on the way to work, it dropped into that rough chugging idle at a stoplight. I checked the codes when I pulled in to work and got: P0131, P0420, and P0171.

At this point after replacing and checking so much I'm starting to run out of ideas. Could it be the bank 1 o2 sensor? I have logs of my drives the past few days, and my fuel trims are going crazy. Close to 0 when driving, then up to 30% when I let off the throttle. My o2 sensor voltage also seems to be dropping all the way to 0 when I let off the throttle. I should also mention it has no catalytic converter (the guy I bought it from took it off and replaced with a test pipe that came with the headers).

 

This is a finicky issue, due to deleting the CAT its almost guaranteed to throw 02 related codes. Unless the car has been tuned to not adjust to 02 readings. If you know for sure that fuel trim adjustment from 02s has been disabled, its likely not going to help throwing new 02s at it.

Best advice i could give,
- Put a CAT back on so the ECU can adjust fuel accordingly
- Find a tuner familiar with minis, who can disable the 02s trim adapting
- live with rough idle

Lastly, P1498... the plague of R53s. This code is a bugger, and does not always show up. My R53 for example likes to throw this after extended periods at idle, but could cruise at speed for a year without throwing the code. When an air leak becomes bad enough you'll end up with misfires, especially around the charge pipe. If the car is continually hunting around at idle you have a vacuum leak that can and would cause chugging, BUT seeing as the test pipe is questionable i would be concerned about that over anything.

Best of luck

 

im not a tuner but I don't think you can disable both O2 sensors. you would disable the post cat sensor if you do not have a cat or did not want a reading there.

I'm going to take a guess. just a guess after dealing with two mini's (r50 and r53) for years now.

you have a sensor problem. probably the tmap. but maybe others also.

just start replacing them, one at a time. OE SENSORS ONLY. do not try and save money here

tmap, map, o2, crank, cam

or you can learn how to test each sensor. Something I have read about and seen but never learned how to do

 

I like this, glad we came to the same overall consensus. I think your right to start with the vacuum related parts, I'm just confused how the cars acting not being able to adapt fuel trim correctly.

I'd also suggest to let the car idle for 10 mins, again my car will not throw 1498 above idle. But if I idle for 5-10mins 1498 comes back along with the EML. I also have the random idle hunting but it doesn't "chug" so have not looked further yet personally, and don't care until its an issue.

Hope the OP can find a solution, but the no cat thing is sketchy to me unless your full blown racecar!

 

Just ordered replacements for both O2 sensors, tmap sensor, and a PCV valve. I've driven it probably 10 times since I made this post and the issue hasn't gotten worse or better. It sounds feels like an older carbourated engine when it's not getting the correct air fuel ratio for the first 20-30 seconds, then evens out. Only codes I'm consistently getting are P0420 and P0171 (cat converter efficiency under threshold, and system too lean). Would it make sense to look at the fuel pump? I don't have any issues past the initial startup idle, so I'm inclined to agree that it's a sensor issue.

 

you could check fuel pressure

the fuel pump would be my next move if the sensors dont solve this.

dollars to donuts the sensors fix your issue

 

Alright, I replaced the PCV valve and map sensors (did the intake side earlier this year when the issue started, and thermostat side today). When I started it up, I didn’t have as bad of a chug, but still a rough idle. When I tap the throttle it hesitates at first. When I let off it almost stalls out. I shut it off and restarted it once, and it acted about the same. I have the replacement o2 sensors, but have to wait for a non-rainy day to swap those out.

I did get a new code upon replacing the thermostat side map sensor: P1239 Speed fuel pump positive feed fault. And still have the P0171 and P0420 codes for lean mixture and cat converter system bank 1 efficiency below threshold.

I’m hoping to throw in the new o2 sensors one day this week if rain permits.

 

Almost forgot to add - after I swapped the map sensors my logs showed that the short term fuel trim lowered to a more reasonable level, ranging from -10 to +10%, but long term is still around -35%. Idled it for 10 minutes then shut it off and started it back up again, and short term fuel trims shot back up to +30%, with long term staying around -35 to -25%. I’m at a loss.

I’m gonna stop thinking too much about it until I can swap out the o2 sensors.

 

short term at -10 through 10 some would say is normal

dont forget to reset adaptations after you replace each sensor

 

Didn't think about resetting adaptations. Good call. I'll post an update once I have the o2 sensors in and find out if that changes anything. Someone on reddit said it would be worth checking fuses and relays for the fuel pump too since that P1239 code popped up.

 

Replaced the 02 sensors and reset the ECU - no changes. I checked out fuses and relays and didn't see any issues. Even swapped the fuel relay for another proven good one, without any changes of course. Tearing my hair out over this, as I've been driving my mother's spare car for almost 3 months now.

I'm beginning to think it's vacuum related though, since it only happens during idle. No issues once throttle is triggered. And logs reflect that too, showing that fuel trims drop to normal levels when the engine's at higher rpm than idle. It seems I'm going to be going over the whole intake system again.

 

bummer to hear. time for a smoke test?

 

I believe so. It's hard to tell what's going on without.

It sounded like the fuel pump was struggling to prime at the first keyturn when cold, so I installed a new pump and housing since the other was at 170k miles and 20 years old. I drove it to get a new tank of gas thinking it might have been a reaction to switching to the summer blend this Spring. It ran fine and pulled like normal, then I got the same chugging misfire when I started it back up at the gas station.

The P1239 code seemed to be related to the non-oem MAP sensor I installed, so I put the old back in and cleared codes. Hasn't come back. My p0171 lean mixture code hasn't come back yet, surprisingly, even though logs show that short term fuel trims are still spiking to 30% shortly after letting off the throttle. I'm half tempted to just drive it for a while and see if it goes away, but the idea of running it with such a lean mixture doesn't sound safe.

This issue is an enigma.