Another Lumpy idle A class.
07-14-2020, 05:54 AM
#1
Another Lumpy idle A class.
Hello All. 
Another case of the engine hunting at idle when warm, can anybody please help?
I have An A180CDI 2ltr 2009 Diesel Auto (CVT). When the engine warms up the idle hunts intermittently. I've removed the airbox and have piped the vacuum system to run without it (for observation). The problem remains.
I've checked all the vacuum pipes and cannot see any evidence of splits/leaks. I've removed the EGR valve and body and Throttle body (pig of a job) and have cleaned them until they were like new. The problem remains!
Disconnecting the EGR vacuum solenoid immediately cures the lumpy idle. Alternatively, removing the vacuum pipe to the EGR valve cures the problem. Finally, unplugging the MAF also stops the intermittent lumpy idle.
The only clue I have is that when the rough idle appears the Duty cycle reading for the Y31/13 (EGR [ARF] vacuum transducer / throttle valve) starts jumping all over the place. But no fault codes are ever thrown up!
Often when warm the engine will idle beautifully, but I can sometimes induce the lumpy idle by dabbing the throttle to raise the rpm briefly. When the rpm returns to idle the engine will then Hunt, sometimes for a few seconds, sometimes for minutes, but will then settle to normal! Could this be an EGR problem, a throttle body problem, or even an EGR vacuum solenoid problem? Otherwise the car drives fine with no error codes.
I would appreciate any help anybody could offer with this, its driving me bonkers.
P.S. The system seems to hold vacuum perfectly overnight.
Many thanks, Gerald.
Another case of the engine hunting at idle when warm, can anybody please help?
I have An A180CDI 2ltr 2009 Diesel Auto (CVT). When the engine warms up the idle hunts intermittently. I've removed the airbox and have piped the vacuum system to run without it (for observation). The problem remains.
I've checked all the vacuum pipes and cannot see any evidence of splits/leaks. I've removed the EGR valve and body and Throttle body (pig of a job) and have cleaned them until they were like new. The problem remains!
Disconnecting the EGR vacuum solenoid immediately cures the lumpy idle. Alternatively, removing the vacuum pipe to the EGR valve cures the problem. Finally, unplugging the MAF also stops the intermittent lumpy idle.
The only clue I have is that when the rough idle appears the Duty cycle reading for the Y31/13 (EGR [ARF] vacuum transducer / throttle valve) starts jumping all over the place. But no fault codes are ever thrown up!
Often when warm the engine will idle beautifully, but I can sometimes induce the lumpy idle by dabbing the throttle to raise the rpm briefly. When the rpm returns to idle the engine will then Hunt, sometimes for a few seconds, sometimes for minutes, but will then settle to normal! Could this be an EGR problem, a throttle body problem, or even an EGR vacuum solenoid problem? Otherwise the car drives fine with no error codes.
I would appreciate any help anybody could offer with this, its driving me bonkers.
P.S. The system seems to hold vacuum perfectly overnight.
Many thanks, Gerald.
Last edited by Jetjockey145; 07-14-2020 at 06:15 AM.
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uivilstyle (05-06-2023)
07-14-2020, 01:48 PM
#2
Update.
I've swapped the two vacuum solenoids over but the fault persists exactly as before. I've also tried a replacement Boost pressure temperature sensor and the fault persists exactly as before.
Dohh!!
I've swapped the two vacuum solenoids over but the fault persists exactly as before. I've also tried a replacement Boost pressure temperature sensor and the fault persists exactly as before.
Dohh!!
