The Yo-Yo Chronicles

Yo-Yo: Vehicle exhibits a characteristic where the throttle body is oscillating, causing audible and sometimes physical "lurching" or "wavering". The Yo-Yo is applicable to the MINI Cooper S only, a vehicle that is supercharged, drive-by-wire, EGR-less, and returnless fuel delivery. Yo-Yo is found sporadically throughout all software versions from 31 to 36, however most prevalent with MY04's.

My MY04 MCS Case:
-Vehicle has exhibited Yo-Yo since delivery
-Yo-Yo is more prominent when engine is cold, however prevalent at all times
-Yo-Yo does not alter with the modification of: CAI, cat-back, supercharger pulley ratio, spark plugs, coil pack, ECU mapping, V35 vs. V36 algorithms, wheel/tire combo, and suspension configuration, or engine oil.
-Yo-Yo changes characteristic when MAP sensor is unplugged, changing from low frequency high-displacement throttle-butterfly oscillating and subsequent intake pressure oscillation to high frequency oscillation and low-displacement throttle-butterfly oscillation. When MAP is plugged back in (regardless of resetting the ECU), high frequency characteristic maintains with reduced magnitude, accompanying low frequency oscillation.
-Since Yo-Yo amplitude is engine temperature related, concept of poor O^2 sensor is ruled out due to open-loop mode during warm up cycle.
-With MAP sensor plugged in, Yo-Yo only occurs near zero vacuum and positive boost, part throttle, and medium load. Yo-Yo does not occur during non-boosted acceleration or 80%+ “WOT” open-loop running, nor does Yo-Yo occur above 4k RPM in any gear.
-With MAP sensor unplugged, Yo-Yo occurs in any gear and any RPM from low vacuum to any boost, with exception being high vacuum “coasting” and 80%+ “WOT”.
-Since the system maintains the Yo-Yo regardless of MAP involvement; MAP seems not to be the problem. The change in characteristic due to the MAP being in the circuit could be the result of the ECU trying to adapt via the throttle body according to the correct but poor data read by the MAP sensor via the initial oscillation by the throttle body, creating a vicious circle.

Hypotheses include bad throttle body solid-state components, servo may be incorrectly responding to logic outputs, or outputs may be processing incorrectly. Probability of servo working incorrectly for only a portion of the bandwidth (especially in the middle!) seems unlikely, suggesting the throttle body logic is in err.

Thank you for reading. MINI Division please respond!
Regards,
Ryan

 

Good work Ryan, good work!

Do you know if there is a way to find out (or if you already knew) if the yo-yo is a result of throttle butterfly movement, or is a result of fuel injection fluctuation? I know we have both noticed that yo-yo is audible in the intake/supercharger noise, and this leads me to believe the throttle butterfly actually moves. If it is the throttle butterfly that is actually pulsing, this info may help MINI in fixing this problem.....

 

Good info and accurate descriptions. Is there any way to examine the butterfly in action, say on a dyno?

_________________
Chris
'04 MCS: 1,2,3, aux guages, aux input, dk slvr, blk/lapis blue - delivered 12/22/03

 

Does anybody know if the yo-yo changes with the introduction of a large bore throttle body? And if it does, how does it change.

Inquireing minds want to know.

Cheers,

JD

 

---> Katana, I'm almost positive the Yo-Yo is not related to the fuel injection system. If it were the culprit, the characteristics would be much different (kicking and sputtering, with non-ideal looking spark plugs), and would definitely not cause such obvious induction fluctuation noise. A fuel problem would also not cause such a high frequency pulsing in engine response. Last time I checked my spark plugs, all four looked perfect, which makes me think the fuel system is working correctly.

---> Stew, A dyno is the perfect place to examine the butterfly "in action", since the Yo-Yo only occurs under engine loading. You'd have to remove the induction system in order to expose the throttle body, but this won't be a problem in the "clean-room-esque" dyno facility

---> JD, If the Yo-Yo were indeed the throttle-body fluctuating, a larger-bore would amplify the Yo-Yo due to the higher delta in airflow. Of course, if the throttle-body electronics were the problem, a new throttle body would get rid of the Yo-Yo, thus making the higher airflow potential not a problem. If I was an aftermarket throttle-body manufacturer right now, I'd be making sure my core's didn't come from a "Yo-Yo equipped" MCS!

I'm going to try to pull some teeth at Motor City MINI tomorrow; either the ECU is physcially whacked or the throttle body electronics are screwed. Does anyone with solid engine management background have any other ideas or tests?

 

Does the MCS also use a TPS to track the throttle plate angle?

What if the TPS reads that the throttle-actuation servo has overshot its target position? The ECM would bring the throttle back until the TPS voltage was within its specified range, correct? Now what if the TPS or the throttle servo aren't sufficiently high enough resolution to bring the throttle plate back to its specified range and it undershoots is target? You can see how this could set up a throttle fluctuation.

I only bring this up because this is how '88-'98 Chevy/GMC trucks work the HVAC controls, through a motor that uses a potentiometer to report shaft angle. The actuators fluctuate back and forth for several minutes, overshooting and undershooting the target setting, before eventually settling out.

Maybe I'm talking bollocks. At the least, if there's a TPS, it's easy enough to tap a scopemeter into the wiring, set it up as a flight recorder, and see what happens to throttle angle during the yo-yo.

 

Yes Parklife, the MCS uses a TPS to monitor the servo action in the throttle body - it's all in one sealed unit. Your proposed situation is highly possible, though why it only occurs in a small percentage of mostly '04's can only come down to production tolerance error, it seems. Thanks for your insight!

 

can we narrow down to perhaps a range of build dates for '04s?

where is the build data located? on car or window sticker? I'll look tonight and maybe if we can nail it down to a certain month that may help Mini --- at the end of the day we may end up solving this problem for them.

 

FWIW...my May '03 does it.

 

I think yo-yo has been present for as long as the stumble. Since the stumble is much more dangerous, people pay a lot more attention to it. Now that the stumble seems to have been solved, it is time for MINI to look into the yo-yo.

My guess is that there is either not enough damping somewhere in the system, or there is too much of a delay somewhere in the control loop. This could be a hardware issue, or this could be a software issue..... I really wish we still have mechanical throttles -- it would at least eliminate the yo-yo......

 

To night Ryan and I took apart out cars and switched throttle bodies. We both had V36 added to our cars and I had a big stumble problem that it took care of. The car feels much smoother now, but I had not felt the yo-yo in a while so I thought maybe it was gone. After switching T.B.'s his car still had the yo-yo, a bit different than the other yo-yo with his T.B., but still there. So we put mine back on my car and he took my car for a drive. He was able to produce the yo-yo in the lower gears at lower RPM's. I guess I never notice it because I drive the car a bit faster than he was driving. When I started to think about it I only notice it when I have guests in the car or I have a heavy load in the back forcing me to drive slower so I do not throw people/things around inside the car. And that requires me to give it less gas and shift a bit lower. When I drive the car more like an old man. So my cure is to drive as fast as I can (and on a bone stock car that is not too fast)…lol. But really he is the tech guy so I leave the thinking to him, and I am the wrench since he is not allowed to use the screwdrivers any more. Hope the thumb heals quickly!

 

Chad - I took the bandage off tonight - my thumb looks yukkie

There are only a handful of components that are even involved around the throttle body action. To refresh quickly, the throttle butterfly is what I can hear oscillating, and "see" with my boost/vacuum gauge via intake manifold pressure fluctuations:
The Throttle body assembly (butterfly, servo, logic, TPS), MAP sensor, ECU, associated wiring harnesses, induction system (air filter and hoses), Bypass valve, supercharger, and intercooler.

It's not the induction system; neither the stock nor my ALTA w/tube affected Yo-Yo
It's not the MAP due to known-good parts swapping
The throttle body isn't likely, though both vehicles tested have the Yo-Yo
Supercharger or intercooler isn't likely, due to temperature-related and narrow-band character of the Yo-Yo.
Wiring harnesses not likely - would cause less predictable results and/or cause faults and related error codes
ECU possible - physical fault possible, software not as likely due to multiple types of algorithms and maps.
Bypass valve - possible, vacuum operated nature could account for rhythmic and predictable nature, one of the few parts not ruled out.

Hmm, I have a feeling it's the bypass valve now. I'll work on this tomorrow.
Until next time,
Ryan

P.S. I had Mark Ferguson forward this thread to the product manager at MINIUSA. Hopefully this will help expedite a solution!
P.P.S. My '04 MCS is a 10/03 build - one of the last that was loaded in Oxford with V35.

 

I wanted to add the following:
The condition that causes yo-yo in my car is very specific. It occurs at partial throttle (around 30% pedal travel I'd guess, not WOT) with load (passengers, or going slightly uphill). There is this small hill between the highway and my house, and my car yo-yos everytime it climbs that hill. It is very reproducable. It is not there in 1st gear, but present in 2nd thru 6th gear.

My gut feeling is that it is another software issue. The gain setting to control the throttle butterfly needs to be tweaked is my guess......

 

Ryephile: I'm with you on the bypass valve. My bet is its leaking or not going all the way closed.

 

I didn't get a chance to test my bypass valve today, though my peers feel it's most likely the ECU programming - an instability in the code that MINI has not discovered yet. Why it occurs in some and not others is still a mystery.

---> Katana, you can get it to yo-yo in all gears including 1st. Most of the time you spend so little time in 1st, and it's under such relative low engine load, that you don't feel it. It's easiest to feel it in 1st with a bone-stock MCS.

 

I am on the thought train that it is related to the supercharger bypass valve!

 

>>---> Katana, you can get it to yo-yo in all gears including 1st. Most of the time you spend so little time in 1st, and it's under such relative low engine load, that you don't feel it. It's easiest to feel it in 1st with a bone-stock MCS.

I've never gotten it to yo-yo in first gear..... I guess I just haven't discovered the "right condition" yet...
Time to go drive more...... :smile:

 

Hello all. FYI. I'm a 12/03 MCS with the yo-yo in 1st and second. Mainly with passengers and mostly around 2900 rpm, if memory serves me. I also have the latest software version 36 and it was great for the first few hours and then...business as usual. I'm thinking about changing vehicles soon if MINI doesn't come up with some reasonable solution. I was going to look into an M3, but I might be soured on all things BMW. Please, MINI take notice. I can spend my money in many places...even more expensive vehicles, but I love my car and don't want to have to get rid of it, but I also don't want to keep dealing with this sub-standard quality. It wold be one thing if the MINI had only been out for a few months, but that is not the case. PPLLLLLEAAASSEEE, somebody help and listen.

Fhew! Sorry about that. I feel better now.

I'm interested to see what all the brains on NAM.com come up with, since it may be my only hope. Thanks for all the input.

Best,

J.

 

Dropped mine off this morning for v36. It appears that this will not help the yo-yo, as some other people have reported.

The interesting thing to me was they gave me a 2004 Pontiac Grand Prix to drive. I was looking at this car when I decided to get the MINI.

I guess I am getting old. The squeak free interior, stumble free take offs, and the yo-yo less part throttle acceleration really have me second guessing my decision. Like I said, I must be getting old.


The blow off valve was told to me by my dealer to be the cause of th yo-yo. The service advisor also told me it goes away after 3,000 miles, which is obviously not the case.

I had pm'd Ryan earlier with a half baked idea that belt slippage could be what we are feeling since it occurs at about the time load is increased on the pulley, and boost is visibaly effected. I came to this wild notion because I witnessed a car that had reportedly never yo-yo'd in 50,000, suddenly develop it after the belt had been removed and reinstalled, on a exteremely cold day. Ryan was nice enough to reply. His investigations were much more scientific, and I felt that the belt problem would most likely be a known problem by now.

Last months Sport Compact Car had a article on a EVO they were adding mods too. They showed a dyno of the modded car and pointed out how uneven the power was up top. The said this was due to the knock sensors telling the ECU to reduce timing. The ECU would, then give it back, then have to take it back. I would be curious to see how the dyno pull of a yo-yo car would look, while at part throttle. The AFR measurements during a yo-yo would also be interesting.
I wonder if it's possible the car is doing, or thinks it doing what it needs to do to prevent knock.
It would explain why resetting the ECU seemed to make it worse on my car, since all previous data was lost. Winter fuel arrived here the same time frame as well.
Just a thought.

 

--->gmack, our service advisor Ilya must've told you that "bypass valve causes the yo-yo until 3k miles" line too. It makes no sense technically because the bypass valve is vacuum operated and had no bearing on mileage, be it 300 or 300,000!

I've been at the Press Conferences for the NAIAS for the past few days - so I haven't been able to even drive my MINI, let alone investigate. Seeing the new car releases and drooling over the concepts up close and in person have me not so excited to get back behind the wheel of my Yo-Yo'ing Mr.Motor2

 

well, add me to the "greener pastures" list. I actually went and retest drove the other car I didn't get and it was so smooth, quicker and softer over the bumps. Yes, I too am geting old.

We had a Subie WRX wagon press car this weekend and the factory short shift kit on this demo was so notchy it would be worse than the yo yo on a daily basis. ugh!

 

I had v36 loaded on my car. Got to meet Ilya, he treated me well. Spoke to Bill at MCM this too also very nice. My car was not ready. No fault of there own, a mouse has decided to make a nice winter home in my car and has helped himself to some lovely snacks. Non-waranty repairs of course. The parts are on order. MCM called the contact number I gave them, so I don't blame them. This was my first visit to the new building and I have to say it was pretty positive. :smile: They took it upon themselves to fix my sunroof rattles, eventhough I didn't ask them too. I guess they are showing off since there lessons learned on Christians car ? Thanks Christian, sorry you had to the guiney pig.

My car has a much improved yo-yo so far and no sign of a stumble. Every time I took off, I intentionally tried to make it yo-yo. Out 15-20 take offs, I succeded once, and only once. I am baffled why it hasn't improved it for everyone. If my car stays this way throughout next summer, it would be tolerable. I hope it stays this way and that the mouse in my garage dosen't suffer too much this evening.

 

Hey Rye, one of your November club buddies here to share my 04 MCS yo-yo experience.

Knock on wood, my yo-yo is very slight. It's most pronounced when the car is cold, especially first thing in the morning. It tends to appear above 2500 rpm in 1st and 2nd gears; no yo-yo in 3rd or higher. And it pretty much disappears after driving for 5-10 minutes. At least in my case, the phenomenon seems to be related to engine temperature.

My car is a 10/13 build, totally stock. Not sure which software version that would give me, but there's no stumble.

Keep up the good work. You're the Sherlock Holmes of Yo-Yo.

 

My car will yoyo only if it's not warmed up before take off and only in second gear. Once the car reaches it's normal operating temperature it's flawless :smile: I did have v36 installed over 1000 miles ago and I'm very happy. I always wait for the car to warm up because it's good for me and my car. Stumble and yoyo free, loving it. The yoyo felt like a flat spot on a badly jeted or maped motorcycle but not terrible, I would have had no problem living with it considering the fun factor driving this car vs. gremlins. My aprilia motorcycle is known for having a flat spot between 3000 and 4000 rpm, after modifications to the air box, exhaust and chip it is a lot better but not perfect. I would never sell that bike for the same reasons I keep my mini. They are fun machines even if they aren't perfect. I hope yoyo is your worst problem, good luck to you all.
:smile: :evil:
It's all good.

 

Just to clarify: According to Erik Luchsinger, MINI factory rep dude for the Southeast, ALL MCS's have the yo-yo.... it's just more noticable in some than in others. Mine is a June 2002 build and the yo-yo is severe.