Technical Why is my engine idle inconsistent?

[Fiat500Fiat500Fiat500]

Hi, was wondering if anyone else experienced the same issue with an inconsistent idle, as you can hear in the video the intervals are approx 5 seconds and you can see the engine shakes as if it will stall.

Any help, much appreciated.

Thanks.

 

[Mike1alike]

That rhythmic dip every few seconds isn’t normal “lumpy idle”, and the fact it’s so regular points to the ECU actively trying to correct something rather than a random misfire.
On these engines with VVT, a very common cause is VVT control not behaving properly at idle. The ECU commands advance/retard, doesn’t see what it expects, then corrects again, which shows up exactly like this: rev dip, engine shake, recover… repeat.

Things I’d be looking at first:
Oil condition and level - VVT is oil-controlled. Old, thick or low oil can cause delayed VVT response.
VVT solenoid - they can stick or react slowly without throwing a fault code.
Oil filter quality - collapsed or wrong spec filters can affect oil flow to the VVT.
Vacuum leaks (especially intake hose, brake servo line) which can exaggerate the dip when the ECU corrects timing.
Throttle body cleanliness/relearn if it’s been disturbed.

If it were ignition-related, you’d expect randomness. This is too regular for that.
A scan with MultiECUScan looking at requested vs actual cam phase at idle would be very telling here.

 

[Mike1alike]

Also worth noting from the video that the rocker cover area around the VVT solenoid looks quite oily.
A leaking rocker cover gasket or VVT solenoid O-ring can let oil seep externally (what we see) and sometimes affect oil pressure/flow locally to the VVT control, which can make VVT response slow or inconsistent at idle.
It’s not uncommon on these engines, and it ties in well with the regular idle dip seen in the video.
Definitely worth cleaning the area, checking for an active leak, and inspecting the gasket/VVT seal while the solenoid is out.

 

[The Panda Nut]

Dirty throttle body, restricted airflow, oiled MAP sensor. would be my hit list. I would be suprised if its not the former. These things need cleaning on a regualr basis. Frequency depends on the engines basic health. If you want the engine working well then the VVT does get tardy buy it main operation occurs above 3600rpm. It does affect the lower speed pull I have found but Im unconvinced it will affect idling as it should be at rest. Its a job thats well worth doing though.

 

[Mike1alike]

Throttle body and MAP are worth checking, but the very regular timing of the dip makes it look more like the ECU correcting something on a fixed cycle rather than sticky airflow. On these engines that often points to VVT control or oil-related response, especially with visible oil around the solenoid.

 

[A3jeroen]

AC compressor kicking in every 5 seconds?

gr J

 

[Mike1alike]

AC compressor kicking in every 5 seconds?

gr J

Interesting theory.
But... isn't the AC compressor clutch magnetic? Should click quite noticeably when kicking in. I can't hear any click. Worth checking though and easy to check.

 

[sanders007]

Hello, did you have any luck pinpointing the issue? My Fiat has exactly same idle problem. Will be replacing throttle and Engine computer soon as a part of troubleshooting. Will let you know if it helped.

 

[Ralf S.]

Throttle body and MAP are worth checking, but the very regular timing of the dip makes it look more like the ECU correcting something on a fixed cycle rather than sticky airflow. On these engines that often points to VVT control or oil-related response, especially with visible oil around the solenoid.

The solenoid looks new(ish).

If it was after-market/cheapest possible/made in China then it's probably dubious quality and nasty.

Swap it for a known brand and the problem will go away... or to prove it, just fit a second-hand one.



Ralf S.

 

[The Panda Nut]

Id like to see a photo looking down the throttle body. My money would be on cleaning it thoroughly sorting this.
Surely the VVT will be domning absolutley nothing at tick over it will make no difference even if its seized solid?

Look for oil pooled in the manifold. I have found any build up can affect smooth opertion markedly. I am a complete covert to the fitting of a actch can. Benefits get greater as the engine ages as it catches water and oil vapous and prevents them entering the throttle body and manifold. Iwoudl also clean the fire trap in the shorter fatter breather pipe to make sure its not partially blocked. MES might identify any fuel pressure issues that could be behind this. How old is the exhaust system? Maybe there is something odd going on inside the silencer.

 

[sanders007]

Hello again. I managed to solve the problem. After my car spent almost a month at my local workshop, I decided to give up and take it to an authorized FIAT service center. It turned out that the issue was caused by incorrect throttle adaptation. They recalibrated it within one day, and now my FIAT idles perfectly without any problems.


@Fiat500Fiat500Fiat500 I also want to point out that my car used to idle exactly like in your video. During troubleshooting we tried swapping almost every part mentioned here:

• coils
• fuel injectors
• MAP sensor
• throttle body
• engine computer (ECU)
• alternator

In the end, the problem turned out to be strictly software-related. Hope this helps you.

 

[macpoland]

@sanders007 Cześć, jesteś z Polski? W jaki sposób serwis poradził sobie z adaptacją przepustnicy?

 

[Fiat500Fiat500Fiat500]

Hello again. I managed to solve the problem. After my car spent almost a month at my local workshop, I decided to give up and take it to an authorized FIAT service center. It turned out that the issue was caused by incorrect throttle adaptation. They recalibrated it within one day, and now my FIAT idles perfectly without any problems.


@Fiat500Fiat500Fiat500 I also want to point out that my car used to idle exactly like in your video. During troubleshooting we tried swapping almost every part mentioned here:

• coils
• fuel injectors
• MAP sensor
• throttle body
• engine computer (ECU)
• alternator

In the end, the problem turned out to be strictly software-related. Hope this helps you.

Hi, glad you managed to fix the issue, that was a lot of troubleshooting

Thanks for the suggestion, I went to a Fiat specialist and they did a throttle re-learn procedure on their scanner tool, however the rough idle is still there.

My "absolute throttle position" at idle was approx 88.6% before going to the specialist, and after the scan tool re-learn procedure it was still in the same %

 

[Mike1alike]

My "absolute throttle position" at idle was approx 88.6% before going to the specialist, and after the scan tool re-learn procedure it was still in the same %

Why you see ~88% at idle
On many Fiat ECUs the scaling is inverted or offset. Closed throttle often shows ~85–90% and wide open throttle may show ~10–15%.
Yes, backwards compared to what you’d expect.
The “absolute throttle position” reading isn’t a direct % of how open the throttle is. It’s just a scaled sensor value, and on these Fiats it’s normal to see around 85–90% at idle. So the 88.6% you’re seeing is actually normal and not related to the issue.
Can you read the actual throttle position? Isn't there another parameter called something a little different that would show it?

 

[Mike1alike]

Better parameters to watch than that %:
Throttle angle (if available)
Desired vs actual throttle
Idle control status
Lambda / fuel trims

 

[Mike1alike]

I would say the Throttle Body is in working order, so it is out of suspects loop and that keeps pointing toward something the ECU is actively correcting at idle, like cam timing (VVT) or mixture control.
Also, it’s always worth checking grounds and connectors (especially if the car has seen moisture), but the very regular nature of the idle dip usually points more towards something the ECU is actively controlling, like fueling or cam timing. Still, if you have a multimeter on hand, do some voltage drop testing, especially on this BCM (plus many others) ground point feed.

 

[Mike1alike]

the rough idle is still there.

Do you have any electrical consumers on when that happens or it does that with nothing on? Like headlights or AC...

 

[macpoland]

Czy masz włączone odbiorniki prądu, gdy to się dzieje, czy dzieje się to bez włączonego źródła? Jak reflektory czy klimatyzacja...

Cześć ja tak mam w Ford ka2 (fiat 500) 1.2 69 2013 - kwadratowy ECU przy silniku . Przy włączonych światłach i nawiewie bieg jałowy w MES skacze od 650 do 720 rpm. Przy wyłączonych światłach i nawiewie jest doskonale. Problem występuje po krótkiej jeździe gdzie temperatura zaczyna rosnąć. Jak odpala się wentylator przy 96 stopniach obroty się stabilizują.

Co zrobiłem w poszukiwaniu usterki:

- świece Ford
- przewody wn NGK
- cewka Beru
- nowe wtryskiwacze z listwą
- nowy evap
- nowy filtr węglowy przy lewym nadkolu
- nowy korek paliwa bo stary już się nie domykał
- nowy alternator
- nowy akumulator
- nowy termostat + płyn chłodzący
- uszczelka pokrywy zaworów + 4 małe uszczelki wewnątrz pokrywy
- nowy czujnik położenia wałka rozrządu
- nowy czujnik położenia wału
- nowa przepustnica 40SMF10 Magneti Marelli (podobno od 2014 jest montowana nowsza, ale ciężko kupić + trzeba przerabiać wtyczkę
- nowe przewody gumowe małej i dużej odmy
- nowa uszczelka przepustnicy pod, i przy filtrze powietrza
- nowy filtr powietrza + Motul 5w40
- nowy MAP
- wyczyściłem czujnik VVT
- nowa przewód uziemienia skrzynia - buda auta + wyczyściłem masy na pokrywie zaworów, na sprężarce klimy, na lewej podłużnicy.
- nowe obie sondy lambda
- dałem też zwykłe żarówki bez + 60%
- licencja MES brak błędów
- nowy przewód podciśnienia Serwa z czujnikiem

Zauważyłem że podczas jazdy ładowanie jest 14 V, podczas "opadaniu i wzrastaniu obrotów" napięcie biega od 13.6 do 13.9

Jakieś pomysły? Auto podczas jazdy zachowuje się bardzo dobrze.

 

[Mike1alike]

...

Translation:
"Hi, I have the same issue on a Ford Ka Mk2 (Fiat 500) 1.2 69hp, 2013 – square ECU near the engine.
With lights and blower on, the idle in MES fluctuates between 650 and 720 rpm. With lights and blower off, it’s perfect.
The problem appears after a short drive when the temperature starts to rise. When the cooling fan kicks in at 96°C, the idle stabilizes.
What I’ve done trying to find the fault:
-Ford spark plugs
-NGK ignition leads
-Beru coil pack
-new injectors with rail
-new EVAP valve
-new charcoal canister (left wheel arch)
-new fuel cap (old one didn’t seal anymore)
-new alternator
-new battery
-new thermostat + coolant
-valve cover gasket + 4 small internal seals
-new camshaft position sensor
-new crankshaft position sensor
-new throttle body 40SMF10 Magneti Marelli (apparently newer type used after 2014, but hard to find + connector modification needed)
-new small and large breather hoses
-new throttle body gasket and air filter housing seal
-new air filter + Motul 5W40 oil
-new MAP sensor
-cleaned VVT sensor
-new gearbox-to-body ground cable + cleaned grounds on valve cover, AC compressor, left chassis rail
-both lambda sensors replaced
-also fitted standard bulbs (no +60%)
-MES licensed version – no errors
-new brake servo vacuum hose with sensor
I noticed that while driving, charging voltage is about 14 V, and during the idle fluctuation it varies between 13.6–13.9 V.
Any ideas? The car drives perfectly otherwise."

 

[Mike1alike]

@macpoland, the fact it’s perfect with no load but oscillates with lights/blower, then stabilises when the fan comes on, points to a load compensation issue rather than a simple fault.
The ECU is likely chasing the load. Revs drop, it opens the throttle, overshoots slightly, then corrects again.
I’d start with a proper throttle relearn and then look at live data (RPM, throttle position, voltage) during the oscillation. If the throttle response isn’t smooth or the voltage is fluctuating with the revs, that’s where the issue is.