94 R1100 Idle too low

My idle is always low. Planning a long trip I took my R1100 to the dealer and had my choke and throttle cables replaced since they were original. On the visit I asked to have the throttle bodies synced and requested the idle be set up around 1100 where it belongs. Everything was fine on the 100 mile drive home with the choke off. On the next outing the idle fell down around 500 again. I have been in the habit of setting the choke high until the engine temp rises. Then, to avoid the having the engine kill at stop lights I've left the choke on the first notch to keep the revs up around 1000.
Here is the question: Both before and after the cable replacements and adjustments the bike never held idle at 1000 or above without setting the choke partially on. Does this hurt anything? I tried setting the idle with the adjuster screws and could not make a noticeable change in RPM by turning the adjuster screws. I gave up and put the screws back at their original places and went back to keeping the choke partially on. I'm not happy with the thought of a 200 mile round trip to the dealer just to get the idle up when it should have been done on the last visit.
Any advise would be appreciated.
Thanks.

That idle speed ought to be stable and consistent once warmed up. Since it has dropped off again and adjusting the big brass screws (BBS) seems not to make a difference I'd say the air bypass passages controlled by the big brass screws are clogged - thus not allowing the air needed to maintain that higher idle.

Using the fast idle (choke) lever to speed up the idle won't hurt anything but it is a kludge.

If that were my bike I would carefully turn the BBS in until just making closed contact and write down how many turns and fractional turns. Then I would remove the BBS and clean their tips. They spray carb cleaner (I prefer Gumout brand) and compressed air to clean the air passages.

Then reinstall the BBS and put the screws back where you found them. See what the idle is. If low then you need to further adjust and resynchronize the throttle bodies at idle.

A friend has an Oilhead that was doing exactly what you are experiencing. He did just what Paul suggested, including the throttle body sync, and it solved the problem.

Sound advice

Thank you gentlemen. I'll clean the BBS passages, but I don't have confidence in the throttle body balancing since I don't have vacuum gauges. I'll probably take it back to the dealer, tell them where they went wrong, have them redo the work they said they did and suggest they cut me a break on my bill.
I'll come back to this thread when I can post the final result.

An incorrectly adjusted throttle position sensor (TPS) can also cause a high or low idle condition. Something else to consider/check.

...as could valves that are too tight, especially the intake valves (low and/or erratic idle). Sounds like your dealer does most of your maintenance? If so, then they set it to the Facktory spec, and that is too tight.

Also note that tight valves make it much more difficult to get a good balance between the two throttle bodies.

Dirty Idle Port

Thanks for all your help gentlemen. It took a while to get some garage time, but I finally did exactly what Paul suggested and the idle came up a few hundred RPMs. There was also a carbon coating on the idle screws, so I gave them a bath in the Gumout. I even took the time to make a Manometer and check the balance. As Paul said, they needed to be rebalanced. Unseasonably warm here and the grandchildren are all at school so I had some quality time with the beemer.

When I fix one thing, I always see something else that needs attention. The joining cable is too slack. I don't know if that is a problem. But for today, the idle problem was an easy fix and I am pleased.

Thanks again.

New owner

Hello everyone,

Reviving an old thread here. I am 90% confident that my bike is the one the OP posted about. I bought it a little over a year ago.

Anyways, I’ve tried everything I can think of to raise the idle on this bike (94 R1100RS). TB’s are synced. Valves are adjusted. I removed the TB’s and cleaned them with throttle body cleaner spray. I squirt the crap out of the BBS ports. When I put it all together I easily got the idle to 1200 with only 1 turn out. But it seems the very next time I go to ride it resets and idle slow again. Also when it idles low it stumbles or hiccups every once in a while. I can see this on my carb stick when it’s hooked up (mercury disappears during the hiccup). Any ideas?

Denny

dennyd said:

Hello everyone,

Reviving an old thread here. I am 90% confident that my bike is the one the OP posted about. I bought it a little over a year ago.

Anyways, I’ve tried everything I can think of to raise the idle on this bike (94 R1100RS). TB’s are synced. Valves are adjusted. I removed the TB’s and cleaned them with throttle body cleaner spray. I squirt the crap out of the BBS ports. When I put it all together I easily got the idle to 1200 with only 1 turn out. But it seems the very next time I go to ride it resets and idle slow again. Also when it idles low it stumbles or hiccups every once in a while. I can see this on my carb stick when it’s hooked up (mercury disappears during the hiccup). Any ideas?

Denny

Click to expand...

Cables too tight, Air leak, or someone did a zero=zero procedure on it. If z=z was performed you can fix it.

Hope you get that sorted out, and sure you will the more you get familiar with the bike.

I do question what RPM you are trying to set at idle? 1200 is too high and often the lower range when using the "choke" fast idle lever. Most our Oilheads and newer idle closer to 1000-1050ish

Thanks Roger, I did attempt a zero-zero on it last summer. Maybe I need to try again? I used the R1100 maintenance manual that was put together by alot of different folks.

Hen, I hope to figure it out as well. The bike runs great except the idle which has me very frustrated. Otherwise it's a fantastic bike to ride and prefer to ride it on long trips over my R1100S.

Update:

I performed Rob Lentini’s zero-zero TOS reset and the synced throttle bodies again. And... idles perfect at 1200. There’s still a little stumble every once in a while which I noticed was worse today while riding in the rain. So must be a separate issue. Maybe the Hall effect sensor is finally going out?

Denny,
If you end up making further adjustments, the z=z procedure is out of date. Use the z=250 procedure that I’ve posted in another thread.

Also, the correct hot idle speed is 1100 +/-50 rpm.

The details are important in that the Motronic expects the TB, TPS and cables to adjusted to certain specs.

You can find an outline of z=250 (along with the rational) in this thread: https://forums.bmwmoa.org/showthrea...nd-Zero-Zero&p=1091142&viewfull=1#post1091142