idling problem

[davisjj]

I suddenly started having idling problems with my 2002 K1200RS w/36K miles. It starts fine cold and idles normally until I ride it 10 or 15 minutes. Then it dies immediately when I release the throttle. I can only keep it running at a stop light, etc. by keeping the throttle open, and then it smells like it is running rich. It seems to be running perfectly at highway speeds. Is there anything obvious I can check before I take it in to the dealer?

[ShovelStrokeEd]

Vacuum line going from the throttle bodies to the fuel pressure regulator. I'm working with way out of date information here as the last K I had my hands in was my K100 turbo. There used to be one though and its function was to lean out the motor under idle, higher vacuum = less fuel pressure. If yours has cracked or fallen off, that could be the issue. Sure sounds like it.

[Dennis Andress]

I'm still learning my K12 but the vacuum lines are quite different from a K100. All the same, Look for lose or broken vacuum lines around the throttle bodies. Follow the lines to the charcol canister.

[ELP_JC]

-Did it start happening all of a sudden, or did your idle deteriorate progressively until motor died?

-Do you have a dash light?

-What altitude are you at?

 

Well, let's analyze the situation with the information at hand. It's not the pressure regulator since it doesn't have a vacuum input (mixture changes are done by ECU), and bike is working fine otherwise. We can also eliminate injectors, fuel filter, fuel quality, plugs, coils, etc. A vacuum line leak results in a high idle (1.5K rpm); another common problem, but not yours.

 

Next. Bike runs fine cold, then dies when hot. We know our bikes run in 'open loop' when cold, meaning the ECU takes data from all sensors except the O2 one, and calculates air/fuel ratios based on a map (like all other FI bikes without an O2 sensor). Since bike idles fine when cold, that means all other sensors are fine. At operating temperature, the ECU starts operating in 'closed loop' mode, calculating air/fuel mixtures based on data from the O2 sensor, and that's when your problem pops up.

There're only 2 options IMO: bad O2 sensor (cheap), or bad ECU (expensive).

 

I've never heard of a KRS dying due to a bad O2 sensor (doesn't mean it can't happen), but on the other hand, many owners report O2 sensor life of around 24K miles, and you have 36K. My bet is on the sensor.

 

My solution. Based on the above fact, and that you're out of warranty, I'd replace the sensor before starting paying troubleshooting fees of $70+/hr; it's overdue anyway, and quite cheap if you change it yourself. A lot of people are replacing it with a Bosch one, which is half the cost of a BMW (probably made by bosch anyway). Do a search on the i-bmw site. Don't touch it with your hands, and screw/unscrew it with the cable disconnected so you don't damage the wires by twisting them. The only bad news is the connector is under the tank. It's not a complicated procedure; just time consuming. Find a buddy to help you if not up to the task.

 

In the remote case it was the ECU, since there was a 'campaign' (the silent type, BMW style) for bad ECUs (I got mine replaced on my '03), I'd ask for a 'good will' warranty once a dealer identifies it as the problem, but am almost sure a new O2 sensor will solve your problem (cross your fingers). Hope this helps.

Good luck, and keep us posted.

[davisjj]

Do you think the O2 sensor could fail suddenly? My problem cropped up overnight.

[ShovelStrokeEd]

JC,

 

No matter the engine temperature, the bike will remain open loop at idle. It does bring up another point though. The throttle position sensor might be bad here and not allowing the bike to return to idle mode. There used to be a switch on the earlier models that actually told the bike to go to idle but I think that's gone in favor of just the TPS now.

 

It is also possible that the same coolant temperature sensor has gone haywire. Simple to check with a pan of hot water and an ohmmeter.

 

PS, just checked the MAX BMW parts fische and it seems there is still a small limit switch associated with the throttle linkage. I'm not sure of its function as its in a different place but it sure looks like it is contacted by the throttle linkage on return to idle. Might be good to have a look.

[davisjj]

I have put a little over 500 miles on the bike since I first reported this problem, and I may have narrowed it down a bit, although I still don't know how to fix it. The dealer had it for a week, and it ran and idled fine the entire time (figures). After getting it back, I put nearly 400 miles on it last weekend, running two tankfuls of gas w/Chevron fuel injector cleaner through it. It ran and idled fine then too, EXCEPT FOR THE FIRST 15 OR 20 MILES AFTER I FILLED THE TANK. Both times after gassing up it would die immediately whenever I let off the throttle. After riding for a little while it idled smoothly again, and continued to do so until I filled up again. I also noticed that when opening the gas cap to fuel up, I heard a definite "whoosh" of air into the tank. It has never done that before, and I can't help but think it is somehow related to the idling problem. The tank is not venting as it should, and I think that has something to do with the idle problem. Does all that give anyone some ideas?

[ShovelStrokeEd]

Could be a tank venting problem but, I doubt it is the cause of the idle problem. If the tank was building vacuum it would restrict the flow of fuel but not very much.

 

Start the bike with the fuel cap open and see if the problem goes away. If not, you might, through over filling, have flooded the charcol cannister and, when the vent valve is opened after the motor warms up, it is dumping that stuff back into the vacuum lines.

 

I don't have access to the plumbing diagram complete for your bike but you should find out how to remove the charcol cannister and reroute the lines, plugging as needed. I don't think your dealer can legally do this for you but the mechanic might be able to provide some insight.

[JerryMather]

Could be a tank venting problem but, I doubt it is the cause of the idle problem. If the tank was building vacuum it would restrict the flow of fuel but not very much.

 

Start the bike with the fuel cap open and see if the problem goes away. If not, you might, through over filling, have flooded the charcol cannister and, when the vent valve is opened after the motor warms up, it is dumping that stuff back into the vacuum lines.

 

I don't have access to the plumbing diagram complete for your bike but you should find out how to remove the charcol cannister and reroute the lines, plugging as needed. I don't think your dealer can legally do this for you but the mechanic might be able to provide some insight.

The charcoal cannister has three lines on it. Two at the top and one on the bottom. One is coming from the gas tank and the other is coming from the engine area. The single one is a vent line located at the opposite end of the cannister.

Can't we just disconnect the two lines on the top of the cannister, to remove it from the system? And/or connect the three lines together with a "Y" connection and remove the cannister?

FYI: The cannister is located under the tool tray on my '98 KRS, yours is probably there too.

[ELP_JC]

I removed the system entirely (only required in CA). The line that goes to the solenoid disappears, and I recommend you remove the solenoid and associated vacuum lines as well, which clutter the engine compartment, and can cause vacuum leaks (reason I removed it in the first place, since hoses were too big as a result of new supplier in '03, and worked loose more often than not).

Anyway, you'd just have to join the 2 remaining hoses with a simple plastic in-line hose connector. In other words, your tank would vent straight down your torque arm. You'll need to cut one of the hoses some, but it's an easy job. I think I have a pic of my engine after the solenoid is removed (see attachment).