Modern Vespa

I brought my scoot into the dealer last week for a low idle issue. They said the Lambda sensor was tripping a code and that was causing the problem. They sold me the part and away I went. I swapped out the sensor with no problems and disconnected the battery for 15 min or so to clear the computer.
It still idles the same. It idles very low and sometimes stops if I don't catch it quick enough sitting at a light.
I have previously removed the emissions evap system and cleaned the air filter to no avail. So far nothing has made a difference. It has about 7000 miles on it.
I would bring it back to the dealer but they are not available to look at it until next week some time.
Any Ideas?

Tweak the idle stop?

Did it just start with last fill up or has this been happening over severy fill ups? Try using a water remover (or seafoam) in your fuel tank.
90% of the idling/stalling issues in our shop are a result of poor fuel.
The Piaggio diagnostic tester has 3 dots beside each function in the error code menu. If it only had 1 dot marked then it may have been triggered by poor fuel. One dot does not mean the O2 (lambda sensor) is faulty.
Make sure your battery is good also.

There is an idle adjustment for the GTS, but it should only be used if the bike is otherwise well maintained and the idle is consistent. If there is a dirty air filter, old spark plug etc, this adjustment should never be used to compensate. The spec for the idle is 1600-1700 rpm. Since you may not have the shop tool to get a specific reading, you can use the GTS tach. Take the idle up to 4 bars, then back it down just to 3. This should put it in the 1650 rpm range.

Four suggestions:

1. When you removed the Evap system, did you plug the hose that goes into the throttle body (the one that came from the canister)?

2. Battery could be low. Battery should be 12.7 to 13.2 volts when the scooter is off. When running at higher than idle, it should be 14.2-14.5 volts. If it's not, this is probably your problem.

3. As Vespa Burlington said, stale fuel? Put Seafoam or Chevron Techron fuel system cleaner in the tank and run it for 10-15 miles and see if that clears it up.

4. When you cleaned the air filter, did you re-oil it?

Hope you find your problem quickly.

Yes I plugged the hose, I don't believe the fuel is stale. I've been through a few tanks since this began and Yes I did re oil the filter.
I did not however check the battery. I will do that. Otherwise it is maintained very well so I may try the idle adjustment.
I have not looked for that screw yet. Is it obvious?

There is no screw. The throttle position sensor *can* be reset - but don't do this unless fitting a new throttle body - it explicitly SAYS SO in the manual, and I believe it for once.

I bet the throttle body has become oil-mist contaminated - see cheekythomas's posts over the last 24 hours, with full explanations therein.

The only other "idle adjustment" on the GTS is the threaded sleeve that takes up slack in the throttle cable.

True - Idle is controlled via TPS = Throttle position sensor and it can be reset as a last resort (reguardless what the manual says) only after all other checks are good eg..battery, fuel, spark plug and wire to the cap, emissions, O2, valve clearance, debris at throttle stop.

Your first step is to rule out bad fuel -add seafoam and report back

Will do

There actually is a screw at the throttle stop which holds the throttle open a tiny bit more. It has a very small allen key slot in it. Is this what drewteague is referring to?

If that needed to be opened up (it's to prevent the throttle being pulled hard shut by the return cable) then the bypass channel really would need attention!

What's a bypass channel?

See http://www.gtsownersclub.co.uk/forum/viewtopic.php?f=16&t=2188&start=10

Thanks for the informative link, Jim! Thanks to Cheeky Thomas, too!

Cheers,

Bob

Jim, that was the best bit of reading I've done in awhile. So good I've got it bookmarked. Thanks again. And to Tom.

OK...this makes sense now. In a previous post in this thread you said:

"see cheekythomas's posts over the last 24 hours, with full explanations therein."

I searched THIS forum but never did find anything.

Incidentally I think my idle problem was the battery. When I tested it I got the proper voltage at idle but when i loaded the battery i.e. cranked it to start, the voltage dropped to about 7 volts. After further investigation I found all of the cells almost dry. I've since replaced it and have not had the problem since. I will ride it a week or so and report back.

He gave most of the pictures, and a link to the gts forum. Almost dry? Your battery is being 'cooked'. Check your regulator output. with a fully charged battery, go for a ten-mile ride (to ensure it's fully charged again), then measure the battery voltage on the centre stand with revs >4,000 - if over 14.6V (or 15V perhaps to allow for meter errors) the regulator isn't regulating, and will need replacing.

Hey thanks for the suggestion. I did check the voltage because I thought the same thing about the dry battery however I did not check the voltage at 4000 rpm, only at idle.
I'll check on that tomorrow.

So it turns out that the battery WAS the problem with my low idle and engine stalling at stop lights.
After changing the battery that seemed OK, but must've been bad because of the dry cell condition, I've not had one single incident after 100 miles of riding. The battery is not overcharging so I suppose the reason the battery went dry was lack of maintenance on the previous owner's part. (I just bought the scooter a month ago)
Now I'm a little pissed because I brought my Scooter to the dealer (never again) and I would think this would've been checked since it's a know issue.
I did call them to inform them that I fixed the problem myself by replacing the battery. Their response: "That's impossible".