Rough Idle / Poor Initial Pickup New MY17 Stelvio NTX

[TommyR]

Hello all,

This may be "old hat" but I`m still working out how to search past threads to find input on this topic.

My new MY2017 Stelvio idles really roughly, often simply missing a beat and almost stalling before it picks back up and keeps idling. Then when I jump on and open the throttle to take off, there is a momentary total drop-out of the engine as it almost stalls, before picking back up and running "ok". The issue seems much worse at cold start. It sort of feels like it might be a bad vacuum hose connection or something dodgy in the airbox. Has anyone any experience with this?

Thanks - Tom

[guzzisteve]

If it's new I would take it back for it's PDI, sounds like they(dealer) just put gas in it & 'out the door'. Otherwise, get it tuned at a shop.
I read the other thread.
Could need to have things synced & set after having the bike apart for oil leak. Check in Service Manual for hose routing & such.

[randy yocum]

I had the same problem with the 2012 NTX I bought 3 years ago.I learned through the Wildgoose forum how to balance the throttle bodies and reset the TPS (throttle position sensor),After that my Stelvio has run sweet,it starts great hot or cold, runs beautifully right through the rpm range,no more stalling or hick ups.You can find out how to do all this here, just run some searches.

[TommyR]

Thanks Randy, that sounds like the issue...I`ll do the searches and see what I find in T-B balance & TPS calibration.
Tom

[pete roper]

If the poor thing has been apart to have the rear main flange leak sorted and then wasn't tuned afterwards or it was tuned wrongly then it will run poorly.

Have a look at the throttle stop screw on the LH throttle body. Is it still sealed with paint or has the paint been dug out so the screw can be moved? Hopefully not as that screw should never be touched. Likewise the ball joint lock nuts on the throttle linkage. These too should be sealed with paint.

Now to progress further you will need to buy a couple of cables and download Guzzidiag, (Or find someone local to you who already uses it to give you a hand.). After connecting to the bike you will be able to check the calibration of the Throttle Position Sensor, (TPS.).

Now this should sit at 4.8* give or take 0.1 or 0.2 degrees. As long as the throttle stop screw hasn't been molested it should be in this range and shouldn't be touched. If it appears it has been moved get a 3mm Allen key and turn the stop screw until the TPS reads 4.8* again. If the paint on the stop screw is still intact? Leave it alone! As stated above that screw should never be touched.

If the paint on the screw is still intact connect a manometer to the ports on the throttlebodies, close both the air bleeds, start the motor and once warm hold the revs at 3,500/4,000 rpm and using the screw on the bell crank that controls the linkage balance the manifold depression.

Allow the throttle to snap closed and kill the engine with the kill switch, (Not the key.). Snap the throttle closed again and check the TPS reading. If you have moved the bell crank screw the TPS value will of changed and it will need recalibrating with Guzzidiag. Once this is done re-set the trims, again using Guzzidiag, and then re-start the motor. Whichever side, (If either.) has the higher manifold depression at idle, open the air bleed on that throttlebody until the depression is equal on both sides.

Disconnect manometer and reconnect charcoal canister lines, (If fitted.). Disconnect cable for laptop.

Job done.

To me it sounds like one or both of the lines from the charcoal canister may be disconnected or leaking but it probably needs a tune as well.

Pete

[Kent in Upstate NY]

Plug caps? My Stelvio has been flawless but that is most likely that Moto International set it up.

[TommyR]

Hah! You guys are gonna love this.

First thing I did was check the valve clearances....as set by the Guzzi factory. Exhaust valves were around 0.1mm clearance(should be 0.15mm) and inlet valves were at 0.08mm clearance (should be 0.1mm). I reset all those. Plug caps we're good, plugs good.
Next I checked the airbox. Hmm, air filter was in upside down and the rubber intake horn was mis-seated to the back face of the airbox. Corrected these items....and hey presto, the bike already runs WAAAY better. WTF? Thank you Moto Guzzi for my RTV less rear flange, my short circuiting riding light, my ridiculously tight valves and my misassembled airbox. What's next I wonder??

[pete roper]

You don't really have to worry too much about the slight discrepancy in the valve clearances,they open up when the motor heats up so no harm will of been done. The air filter thing is weird. I didn't think you could put it in upside down? The paper vanes should be upwards. Yes? Likewise the snorkel on the airbox. If it's installed upside down it would make it difficult to get the seat on surely.

After setting the valves it is a good idea to clear the fuel trims. If you don't have Guzzidiag yet you can either disconnect the battery or pull the main 30A fuse to achieve this. You'll need to re-set the clock afterwards.

Pete

[TommyR]

Thanks everyone for your contributions. Only 4000 miles done. The saga of rough idle, rough pick-up and constant stalling on opening the throttle continues. Took the bike to the dealer who plugged in his Guzzi diagnostic - no issues found but he did reset the Throttle Position Sensor. The throttle butterflies are mechanically linked by a rod-arm and it's still set to factory [yellow paint marks all align] spec.


So why on cold start does the engine stall and die after 5 seconds? I have to do multiple restarts and as it begins to warm up the problem seems to lessen to just very rough idle. On cold start when it fires up, if I open the throttle even gently the engine instantly stalls and dies. When eventually a little warm, the bike runs well above about 2800rpm but as rough as hell below 2800rpm. It sounds and instinctively feels like a vacuum hose problem so this weekend I`m going to pull the tank and airbox and spend a happy morning poking about to see if I can find anything. Does anyone have any pointers?

With thanks - Tom

[pete roper]

Why didn't they sync the TB's? It takes ten bloody minutes! Not much point in recalibrating the TPS if the sync is out the arse. Don't they know how to do it?

Look, before you do anything else just tune it properly. Valves set to 4 thou inlet, 6 thou exhaust, balance the TB's properly and make sure the stepper motor is working properly. If the engine has been over-filled with oil both TB's and stepper may be clogged with oily mank. Check your airbox and make sure it's not full of oil and run the engine oil level half way between the full and add marks on the stick, no higher.

Pete

[Huzo]

Given that most of the drama occurs at the bottom of the rev range and sort of goes “ok” above fast idle, is it worth investigating the stepper and ensuring that it is not being commanded to vary the fuel/air ratio at the wrong times ?
Or the command is ok but the (stepper) motor is reacting wildly ?
Please don’t tell me it doesn’t run a stepper...