Hunting idle, juddering drive?

M

Momorris

Hi All
My daughter has a spirita 1.2 with 47k on the clock. Car was running fine but has suddenly started hunting a little at idle. The revs will drift up and down slightly. However the bigger concern is when driving. The car will suddenly hold back and then release again. Its like an intermittent misfire

Does anybody have any hints on what to check
 
First suspect would be the MAF, check the live data and see if it responds to throttle opening. You can try unplugging the MAF and see how the engine responds, this will throw a code and light which you will have to clear. Also look at the O2 readings, lambda sensors are ultimately a consumable.
 
I put some v power in the tank (may be related, may not)

Well, i cleaned the throttle body last night (didnt look too bad). Still same isssue. Did the throttle position learn and idle settled down but judder/hesitation still happening on driving. Pulled over and unplugged maf and plugged back in again. The juddering/hesitation almost complety disappeared. It is still slightly there but no where near as bad and the car is driveable.

I did notice a bigger pause at 3500 rpm but the car does clear this and then accerates ok.

The spark plugs look old but not too bad so im going to change these anyway. The air filter is new. I have some injector cleaner coming today.

My suspects are
Maf - will monitor on reader when i get the chance
Fuel contamination
Poor injection
The earth issue some people have seen
 
It's usually the obvious suspect, my guess would be that unplugging the MAF prompted it into life. A long shot would be a faulty MAF plug or corroded contacts. A do-able if fiddly job.
 
Cheers gassed up. I think it was actually the map i unplugged? Just to check the connections on top are the throttle fly by wire and maf and the map sensor is seperate?
 
Last edited:
I got the reader on the car today. All at idle. Short term fuel trim will sit at 0 then drift to -25 as car struggles then goes back to 0. The long term fuel trim is sitting at -99. And not moving. Also when the idle is struggling the closed loop switches to OL and fault appears. (On code reader where CL and OL are indicated). Car then switches back to CL and idles ok.

Repeat the above contantly.

Im going to try the o2 sensors unless somebody has other ideas
 
My K11 showed similar symptoms at idle, it would switch between OL and CL, the rpm would "hunt" and it throw a "too lean" fault code. Turned out to be the IACV, my assumption was that the ECU got confused and was attempting to compensate because the IACV was not responding correctly. I changed both O2 sensors, the MAF and stripped the harness out of the car before the solution slapped me in the gob. The clue came when I noticed the erratic idle steadied when the cooling fan came on, the electrical load prompted the ECU to open the IACV when it was already open, symptoms disappeared.
 
Well, it might be fixed.

I unplugged the second o2 sensor and idle settled down. I then changed the sensor and idle is smooth and steady. The st trim is now fluctuating around 0 with probably more time being spent above 0 by 1 or 2 percent. I left idling for 10 minutes and no struggle or fault on reader. I need to test again when cold but fingers crossed
 

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