Technical Barchetta Throttle issues

[Elianw]

Hi everyone,
Long time reader of the Forum as i've owned quite a few seicento and cinquecentos over the years. I've finally decided to make an account and a post dedicated to an issue with my '96 barchetta which I've had for about 6 years. It's always been a brilliant car and currently sitting at a healthy 90k km.
Last year it started developing a weird habit where it seemed that the throttle cable would stick and keep the throttleblade pulled open for a while after acceleration. I've replaced the idlevalve and things seemed to improve but it never fully went away. Last week the issue returned and worse than ever before.
When you stab the throttle paddle, or the arm on the throttlebody, the engine accelerates as expected. When closing the blade, the engine seems to stick to the same rpms after which it drops down to a normal idle. The higher the revs, the longer it seems to stick.
I've checked all hoses with brake cleaner and have not seen any response on the engine. I'm really lost as what this could be as it seems like a huge vacuum issue but I can't seem to find where it's coming from. Help!

I've attached a video in which I stab the throttle, it is very clear the engine keeps revving and drops down after a short moment.

 

[wapper]

If it's not mechanical, and not a vacuum leak, I'd check TPS connector and readings in MES (not sure if it's possible, hope it is). Perhaps also have a look on the idle valve stepper motor.
Here's what AI thinks https://www.perplexity.ai/search/i-have-a-car-fiat-barchetta-fr-3_wUvrk2Q0iVUBDlWuy9YQ#0

 

[s130]

Worth checking, and possibly a cause, is the Variable Valve Timing.

I can't remember the exact RPM (somewhere between 1700 and and 4700 rpm VARIABLE) the VVT will kick in and change / increase the idle speed.

You can test this by raising the rpm slowly from around 1500 rpm in small steps and holding steady for a while. At around 2K (or possibly 3K) you will note that your held steady RPM will suddenly increase as the VVT kicks in.

By blipping the revs to 4K the VVT will definitely kick and potentially keep the revs lagging the throttle position. Under normal driving with load and drag on the engine you would not notice anything but it neutral with no load things will be different.

 

[Elianw]

Worth checking, and possibly a cause, is the Variable Valve Timing.

I can't remember the exact RPM (somewhere between 1700 and and 4700 rpm VARIABLE) the VVT will kick in and change / increase the idle speed.

You can test this by raising the rpm slowly from around 1500 rpm in small steps and holding steady for a while. At around 2K (or possibly 3K) you will note that your held steady RPM will suddenly increase as the VVT kicks in.

By blipping the revs to 4K the VVT will definitely kick and potentially keep the revs lagging the throttle position. Under normal driving with load and drag on the engine you would not notice anything but it neutral with no load things will be different.

Noticable vvt change happens around 5k rpm I believe, but could be worth checking out. If it is stuck it might give some weird results. Thanks!