lumpy/rough idling and jerky acceleration and poor power - Alfa Romeo Forum
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(Post Link) post #1 of 5 Old 22-11-10 Thread Starter
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156 2.5 V6

lumpy/rough idling and jerky acceleration and poor power

Hi, just wondering if anyone had any ideas on this one:

Bought a 2.5 V6 156 last week, all going well until i notcied a loss of power and when i next when to pull away from a stand still the car had a really lumpy idle and almost jerky pulling away until around 3000rpm.
I've unplugged the MAF sensor and it makes no difference, it smells like it is running very lean and not running on all of its 6 cylinders on idling. I've tried running on a longer joruney and still feels underpowered and hasnt helped at all.

Any thoughts would be appreciated, before a call to the local mechanic.
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156 1.8TS


I have a 1.8TS and had exactly the same problem since getting the car serviced and timing belt change last week. Did my weekly oil level check thinking it should be ok since it was serviced recently, however, it was at the bottom notch on the dipstick. Topped it up and ran the car to and from work tonight (25 mile round trip) and it appears to be cured!! I didn't think that the oil level would make a difference to the extremely lumpy idle but it seems to have.
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Hi , nice to here you have got the 2.5 V6 ..once sorted, it will be superb!!!

Could be a fueling issue but firstly, i would check your air intake (from the MAF to the throttle body) Check for air leaks due to poor connections or splits in the flexi-hose etc.........also check your six chrome intake ducts and their rubber connectors!

A good tip is to buy some carb' cleaner and spray around the items mentioned, if you hear an obvious change in revs, then you are near to an air leak problem!

Your throttle body could also be at fault!

Do a 'Search' on here for Poor idling or Running and you will find plenty of pointers.

Good luck

Arte et Marte, By Skill & by Fighting.

Traded my soul for lifelong car heaven! and poverty !
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Had similar problem with my 2.0 ts. Tried just about everything on here, including the MAF change (albeit for an ebay model as a trial!). Problem got worse with new MAF so put old one back on (anyone wanna buy an ebay piece of s**t?). Changed plugs and leads with no luck. I happened to open the bonnet during the evening and noticed a xmas tree effect within the plug recesses and from the new leads to the coil framework. Turned out the new leads were duff. Changed again for genuine and problem gone now. Car is still a bit hesitant when cold but not yet found out the reason for this.......Any suggestions anybody?

The only other issue I still see is max power with throttle pedal about 3/4 down. On full throttle power drops off a bit. I have checked on AD for the throttle pedal pots and these seem okay so again as do the main throttle valve pots (although when one is 100% the other is 0% so assume they run opposit to each other), if anyone has suggestions on this or can confirm if the throttle position pots are supposed to be opposite to one another please let me know ( no alarms shown for this)!

Hope this helps
mitchok1 is offline  
(Post Link) post #5 of 5 Old 24-11-10 Thread Starter
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156 2.5 V6


had my local mechanic do a diagnostic on it today, seems that the labda is 'sticking' and not running as it should. He has recommended to take it for an emmissions test to confirm, i thinking maybe it needs a good clean or maybe some poor connections to it. Going to have a look over the weekend so i'll let you know how it pans out.
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acceleration , idling , jerky , lumpy or rough , poor , power

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