1999 R1100RT Inconsistent Idle speed....sometime dies at the Stoplight.

This is my son's bike. He bought it last winter...got it for a good price. Needed a tune up and a little brake work. 56k miles. I did the valve adjustment and throttle body sync. It ran great. Idled smoothly on the lift at 1100rpm.

However there is a sort of nagging problem. After riding up to a stop light for instance and letting off the throttle, the rpms will drop down to maybe 700...and sometimes it drops so low that it will die at the stop. If you pay attention to it and keep up the revs gently, after about 2 seconds, the idle recovers and it's running smoothly back at 1100rpms. Even at the brief lower rpms it doesn't seem to run rough or lumpy...it just takes a second or two to recover.

I should add that I took it to the local dealership a couple of months ago and had them confirm that the throttle body sync, etc. was good.

Thoughts?

I'm no expert but I'd check all the common electrical stuff -- Hall Effect Sensor and its wiring, check the ignition coil to see if it's got any cracks in its case, check the spark plugs and test the plug wires with a multimeter, and read the Motronic for fault codes.

What else was done during the tune-up? How recently has the fuel filter been replaced?

senseamidmadness said:

I'm no expert but I'd check all the common electrical stuff -- Hall Effect Sensor and its wiring, check the ignition coil to see if it's got any cracks in its case, check the spark plugs and test the plug wires with a multimeter, and read the Motronic for fault codes.

What else was done during the tune-up? How recently has the fuel filter been replaced?

Click to expand...

The "tune-up basically consisted of a valve adjust and throttle body sync. It might be time to go in deeper. I did not change the fuel filter. I posted this before riding it, going on my son's account. I took it out and my impression is that it runs smoothly and pulls strongly above 4000rpm but with light throttle and suburban riding, it just seems a bit off. Off idle acceleration is kind of ho-hum

banzaibob said:

The "tune-up basically consisted of a valve adjust and throttle body sync. It might be time to go in deeper. I did not change the fuel filter. I posted this before riding it, going on my son's account. I took it out and my impression is that it runs smoothly and pulls strongly above 4000rpm but with light throttle and suburban riding, it just seems a bit off. Off idle acceleration is kind of ho-hum

Click to expand...

Spark plugs?

Injector cleaner?

A gasser that stalls after hot, usually means lean.

Injectors, possible. Don't forget, they have itsy bitsy teenie weenie filters in them.

I might be inclined to review the cold idle with a view to looking for an air leak.

All of the above (plugs: Autolite AP3923), and two more things to look at:

Tight valves will cause a poor idle, especially when hot. The holy Faktory spec is a bit too tight.

Pull the BBSs (Big Brass Screws)(after carefully noting their position) and clean off their tips; these accumulate dirt/carbon junk. Additionally, use a Q-Tip with either alcohol or gas on it to clean out the bottom of that orifice. This path directly affects your idle. If you use a spray cleaner down that hole, protect your eyes.

Pauls1150 said:

All of the above (plugs: Autolite AP3923), and two more things to look at:

Tight valves will cause a poor idle, especially when hot. The holy Faktory spec is a bit too tight.

Pull the BBSs (Big Brass Screws)(after carefully noting their position) and clean off their tips; these accumulate dirt/carbon junk. Additionally, use a Q-Tip with either alcohol or gas on it to clean out the bottom of that orifice. This path directly affects your idle. If you use a spray cleaner down that hole, protect your eyes.

Click to expand...

+1 on the above. Especially the BBS's.

Pauls1150 said:

All of the above (plugs: Autolite AP3923), and two more things to look at:

Tight valves will cause a poor idle, especially when hot. The holy Faktory spec is a bit too tight.

Pull the BBSs (Big Brass Screws)(after carefully noting their position) and clean off their tips; these accumulate dirt/carbon junk. Additionally, use a Q-Tip with either alcohol or gas on it to clean out the bottom of that orifice. This path directly affects your idle. If you use a spray cleaner down that hole, protect your eyes.

Click to expand...

That is very good advice.

I disagree that the factory spec is too tight. After doing valve sets on prolly 10,000 engines in my career, 0.006" intake an 0.012" on exhaust is almost a standard.

I do agree that tight valves will cause a poor hot idle.

But, I'm not an rocket surgeon so what the OE tells me, I believe it to be gospel. I also believe in Santa Clause and the Easter Bunny and that elected officials think that the electorate comes first.

Keep two things in mind, though - it's an air-cooled engine, and will run a little hotter than a "more modern" water-cooled design (or most cars and trucks); and that as the oilhead valve train wears, it closes the clearance downward.
I'm not talking about a "big" change from spec; I run about .007 intake clearance and .013-014 exhaust clearance. Seems to work quite well.

And the Tooth fairy sez the Easter Bunny doesn't exist... I read it on the internet...

Here's where I am at with this:

I also posted this question over at advrider. Got some interesting ideas. One was to unplug the "cat code plug" relay which is the big yellow relay in the middle of the fuse box. My understanding (correct me if I'm wrong) is that it basically no longer reads the O2 sensor and subsequently runs richer. It therefore fuels much better at lower rpms. I did this and I must say that it appears that the ho-hum off-idle acceleration is gone. Low-end response is now sharp and strong.

However......

The low idle problem was still there. So here's where I'm at:

I pulled all of the body panels off and took it out for a warm up ride. I returned and got to work syncing the idle settings on the throttle bodies. First thing I did was to remove the "big brass screws". They appeared to be a bit dirty so I cleaned them with carb cleaner and got them shiny. I pulled the hoses off of the manifold nipples and basically used the BBS to adjust the idle. Turning them out appears to raise the idle on that specific TB. Am I to understand that turning them out leans the idle mixture? Anyway I finally got a good smooth idle at about 1200rpm. I plugged the hoses back in. (Question: those hoses only run the EVAP system, right?) Put the body panels on and went for a ride.

On the ride the idle again fell on its face. Even though it was idling fine on the bench the idle now was between 600 and 800. As it warmed up on the interstate...the idle did not improve.

Took it back to the shop. Pulled the panels off again. Turned the BBS out even more. This time however, I did not plug the hoses to what I guess is the EVAP/Charcoal canister back on. I left them off but instead used rubber sync-port caps, basically sealing them off. Took it back out for a test ride, this time without the body panels. The idle finally seemed to stay up around 1100. Mind you, chopping the throttle from 4000rpm still creates a little fluctuation but not nearly as bad it seems.

What I'm going to do is take it out tomorrow morning after it has cooled down overnight to see if it performs consistently. If the idle stay up, I'm good.

Any thoughts?

Ah, the dreaded charcoal canister.

If you don't live in California, you should pull that thing off your bike ASAP and keep the vacuum ports capped. It sounds like you had a vacuum leak in those lines under the throttle bodies, and by capping them you fixed it.

Over time, the exposure to gasoline breaks down the charcoal in the canister, and the gasoline-soaked charcoal makes its way into the throttle bodies through those vacuum ports. When I popped open my own throttle bodies at just 35,000 miles they had lots of black charcoal residue all over the bores. Plus all the rubber lines for that system end up cracking from age and causing vacuum problems.

Here's a question that I have, it will hopefully give me a greater understand of how the system works:

At idle, the throttle body butterflies are against their stops which are the screw and lock nut on the interior side of the throttle bodies. Can you raise and lower the idle via these screws or is that not procedurally correct? Do the "big brass screws" adjust the bypass air or do they adjust the air/fuel idle mixture? If they adjust the fuel/air mixture wouldn't that lean it out, potentially causing erratic idle? OR....does it control the amount of air that bypasses the butterflies creating a fine adjustment for idle and the engine computer mixes the fuel/air mixture correctly?

Also keep in mind that I like the way that it runs WITHOUT the Cap coding plug so I've removed it.

The BBSs control only the air at idle, since the computer is responsible for adjusting the actual mixture (by controlling the length of time that the injectors are open). Backing them out allows more airflow (up until maybe 5 or 6 turns out, after which it becomes useless).

When the throttle stops are properly set, there is only a tiny margin of butterfly opening at idle; you can see this if you look down into the throttle body. It's also important that the butterfly itself is mounted properly, but that's another thread...
Complete instructions for adjusting the entire setup can be viewed by Advanced-seaching this forum specifically in the Oilheads section and look for posts by Roger04RT; he's done some great stuff. More info can also be found on the Internet BMW Riders site https://ibmwr.org/index.php/oilhead-r-bike-tech-articles/ but this is "older" information and won't exactly match what Roger has written up. He's also done a write-up on the cat-code plugs; which plug is installed depends on not only which engine, but which country and what intake and exhaust setup it has. Removing the plug completely may help at certain RPM, but will be detrimental at other RPM, as it affects the computer's "adaptability".

I agreed that the [silly] charcoal canister should be deleted completely, and the vacuum ports on the throttle bodies must be securely capped off - any air entering thru there is completely unfiltered, and will also affect your sync efforts.

Pauls1150 said:

The BBSs control only the air at idle, since the computer is responsible for adjusting the actual mixture (by controlling the length of time that the injectors are open). Backing them out allows more airflow (up until maybe 5 or 6 turns out, after which it becomes useless).

When the throttle stops are properly set, there is only a tiny margin of butterfly opening at idle; you can see this if you look down into the throttle body. It's also important that the butterfly itself is mounted properly, but that's another thread...
Complete instructions for adjusting the entire setup can be viewed by Advanced-seaching this forum specifically in the Oilheads section and look for posts by Roger04RT; he's done some great stuff. More info can also be found on the Internet BMW Riders site https://ibmwr.org/index.php/oilhead-r-bike-tech-articles/ but this is "older" information and won't exactly match what Roger has written up. He's also done a write-up on the cat-code plugs; which plug is installed depends on not only which engine, but which country and what intake and exhaust setup it has. Removing the plug completely may help at certain RPM, but will be detrimental at other RPM, as it affects the computer's "adaptability".

I agreed that the [silly] charcoal canister should be deleted completely, and the vacuum ports on the throttle bodies must be securely capped off - any air entering thru there is completely unfiltered, and will also affect your sync efforts.

Click to expand...

This is where I'm at right now. I've gotten the thing to idle on the bench (lift) at about 1200 rpm fully warmed (5 bars showing on the temp gauge). Taking it out and riding it; without the coding plug it REALLY runs nice, especially in the lower rpm range. In the higher rpm range I don't really notice a change. Basically ride-ability is all good. However the idle....with it fully warm and doing the "throttle chop" like pulling up to a stop light, the rpms drop down to maybe 950rpm or so. The good news is that the idle is very smooth and it does not die. After about 3-4 seconds, it picks back up to a very smooth idle of about 1100. At this point, as long as the thing doesn't stall I'm kinda good with it. I'm almost of a mind that this is tolerable and whatever is causing the idle to dip under these conditions is something perhaps for another day.

The only thing I guess I'm concerned with now is running the bike without the cat coding plug. From everything I've read (including some of the posts from Roger04RT) running without it means 1) about a 10% or so drop in fuel mileage. Since it gets about 45mpg, 40 mpg is tolerable. 2) Potential damage to the catalytic convertor. Is this really a big deal? Other than a blockage? Couldn't I get an aftermarket exhaust? I don't live in California.

Am I to understand that there are other plugs/fuel maps available? How do I determine which one to use? Where would I get them? Couldn't I disconnect the battery for 5 minutes and reset the fuel map...and THEN re-install the plug? Am I overthinking this?

banzaibob said:

Here's a question that I have, it will hopefully give me a greater understand of how the system works:

At idle, the throttle body butterflies are against their stops which are the screw and lock nut on the interior side of the throttle bodies. Can you raise and lower the idle via these screws or is that not procedurally correct? Do the "big brass screws" adjust the bypass air or do they adjust the air/fuel idle mixture? If they adjust the fuel/air mixture wouldn't that lean it out, potentially causing erratic idle? OR....does it control the amount of air that bypasses the butterflies creating a fine adjustment for idle and the engine computer mixes the fuel/air mixture correctly?

Also keep in mind that I like the way that it runs WITHOUT the Cap coding plug so I've removed it.

Click to expand...

I'm following this topic since I am experiencing a similar issue. My 1100RT runs wonderfully, except that occasionally at closed throttle there is a "miss" and the idle drops below 1,000 rpm and sometimes stalls. I have worked with a friends 1100R and my own RT regarding MUCH WORSE running issues with poor idle, and surging. One thing that I would strongly recommend that you check; that is the throttle position sensor (TPS) idle setting. Check the voltage of your TPS, bike ignition turned ON, but not running. Typically, you might see the closed throttle voltage in the range of 340-360 mv - note that thousandth of a volt - you have to use the lowest voltage setting on your DVM. Adjust the TPS closed throttle voltage to 380-385 mv. You have to stay below 400. Increasing this setting will INCREASE the amount of fuel at idle. It will make the idle richer, which improves idle/off-idle performance. I still have this "miss" so I will check for air leaks the next time the fairings come off.

Aftermarket exhausts for an RT are pretty rare; Staintune used to have one but it's NLA. Be advised that most of the restriction and sound reduction is in the catalytic converter; that's also where a too-rich fuel mix would clog things up.

(Side note: I'm in CA... While the present law clearly states that the exhaust system must have the EPA approval pressed in to it, no police officer would bother anybody whose bike is not "offensive", as long as no other criminal activity is involved - they have better things to do.)

There are maybe 8 (?) different CAT-Code plugs of different colors; they are available at your friendly local dealer. There's a list somewhere of which plug is intended for which bike, but I can't find it now, dang it.

Yes, over-thinking... The computer adapts its fueling map over time, and it has "rough" settings and "fine tuning" that all get tweaked. If you want to re-set the Motronic, it's easier to pull fuse #5 (guys - is this correct for a '99?) for AT LEAST ten minutes than to disconnect the battery.

Well......I guess that I'm just about ready to call this done. Here's what I know:

I took it out yesterday afternoon for a hard test ride. During that time I did quite a few of those "throttle chops" where I accelerate hard at highway speeds, quickly cut the throttle and pull in the clutch. The result was that yes, the rpm would dip down to 700-800 or so. A couple of times it would even stall. I parked it at the grocery store for about 10-15 minutes and came back out and started it up. It idled at about 1500rpm. At this point I'm confused and disillusioned.

This morning I decided to remove fuse #5 for about 15 minutes and let the Motronics reset itself. I then took it out for a normal, sensible ride; no throttle chops, no abrupt inputs. After the engine temp got to 5 bars it would idle normally at about 1200 rpm. I actually went for 2 rides, a 30 mile country/2 lane ride and a 35 miles high speed interstate ride. On both rides I rode normally with normal acceleration and stops. The result was that during this normal operation, on stops, the rpm might SOMETIMES dip a little to just under 1000rpm but it returns to 1200 within 3-4 seconds. I cannot tell you if this means that the problem is "fixed"....but to me it is something I can live with.

Also I wanted to check the fuel mileage since one of the stated problems that might occur from not having the cat coding plug installed was reduced mpg. It appears to get around 42mpg...that is WELL within acceptable limits.

Thank you everyone for all the good advice. I'll keep you posted if anything changes.

Pauls1150 said:

The BBSs control only the air at idle, since the computer is responsible for adjusting the actual mixture (by controlling the length of time that the injectors are open). Backing them out allows more airflow (up until maybe 5 or 6 turns out, after which it becomes useless).

When the throttle stops are properly set, there is only a tiny margin of butterfly opening at idle; you can see this if you look down into the throttle body. It's also important that the butterfly itself is mounted properly, but that's another thread...
Complete instructions for adjusting the entire setup can be viewed by Advanced-seaching this forum specifically in the Oilheads section and look for posts by Roger04RT; he's done some great stuff. More info can also be found on the Internet BMW Riders site https://ibmwr.org/index.php/oilhead-r-bike-tech-articles/ but this is "older" information and won't exactly match what Roger has written up. He's also done a write-up on the cat-code plugs; which plug is installed depends on not only which engine, but which country and what intake and exhaust setup it has. Removing the plug completely may help at certain RPM, but will be detrimental at other RPM, as it affects the computer's "adaptability".

I agreed that the [silly] charcoal canister should be deleted completely, and the vacuum ports on the throttle bodies must be securely capped off - any air entering thru there is completely unfiltered, and will also affect your sync efforts.

Click to expand...

Pauls1150,

Not to hijack the thread, but I would be interested in your comment about properly mounted butterfly plates. I rebuilt my 2004 throttle bodies a few years ago and on the first unit I did not pay too close of attention to the orientation of how it came out nor went back in. On the second unit I was more conscientious to reinstall it in the same orientation as it come out. Not sure if the plate has ever so slightly beveled edges, top or bottom, frontside and backside? I did use feeler gages to get the slight gap equal all around. I did a simple and quick search on the forum and did not find anything that discussed the throttle body butterfly plate installation.

Thanks,

If these are the ones that you recently posted pictures of in another thread (before & after cleaning), looks like you got it right. It is possible to mount them and not have the plates plus screws centered in the bore.

If you back off the throttle stop screw and see that the plate is sitting concentric in the bore, that's good;
If you set/sync the screw and cables so that you see a very slim, smooth and even arc around the perimeter, that's also good.

Back around July of 2018, BeemerMyke had a worn butterfly to replace.

I don't know if they're beveled, or have a front and back, or a top and bottom ... Anybody?

BTW, in the airheads' Bing carbs, those actually do have a "shape" that must be adhered to when installing.

> PM sent.

Google Dan Cata.
He supplies the throttle shaft kits.
He has a comprehensive how to procedure available. https://www.advrider.com/f/threads/r-1100-1150-gs-rt-rs-r-s-throttle-body-repair-kit.630335/
Correct alignment in the bore is critical
This vid is also helpful https://www.youtube.com/watch?v=eRR5LMQzDGk&ab_channel=AlsmotorradBmw

Roger 04RT has the calibrating procedure for the TPS.
https://forums.bmwmoa.org/showthread.php?73962-TPS-Alignment-Idle-Speed-Adjustment-Beyond-Zero-Zero


Butterfly is not beveled