Engine hunts during warm up
#1
Engine hunts during warm up
I have an XK8 Coupe, 4.2 litre, MY 2003, Engine No. 0207021307, 74000 km.
During the warm up from a cold start, and particularly in the last few minutes of the warm up, the engine RPM oscillates, say about 50 to 100 rpm at light throttle and as much 100 to 200 rpm at heavier throttle settings. As soon as the engine has reached the normal run temperature the problem disappears and does not return during that day even if the car stands idle for a few hours.
The problem will be there again with a cold start the next day. Ambient temperature and humidity have no influence. No fault codes come up.
Has anyone experienced this problem? Can you suggest a cause and cure?
I would appreciate any advice.
During the warm up from a cold start, and particularly in the last few minutes of the warm up, the engine RPM oscillates, say about 50 to 100 rpm at light throttle and as much 100 to 200 rpm at heavier throttle settings. As soon as the engine has reached the normal run temperature the problem disappears and does not return during that day even if the car stands idle for a few hours.
The problem will be there again with a cold start the next day. Ambient temperature and humidity have no influence. No fault codes come up.
Has anyone experienced this problem? Can you suggest a cause and cure?
I would appreciate any advice.
Last edited by colinturner; 05-03-2011 at 01:54 AM.
#2
#3
Same thing happened on mine, various vacuum leaks present...passenger side, between PCV to the throttle body lower elbow was the worst, driver side TB to breather line also slight leak. I removed each line, carefully cut off the norma connectors, replaced the rigid plastic lines with rubber fuel lines (5/8" passenger, 3/8" driver) and worm-clamped em' back onto the norma connectors...replaced the dry brittle o-rings on the normas and re-attached. Huge improvement.
Clean your MAFS while your at it so readings are true to the ECU.
Clean your MAFS while your at it so readings are true to the ECU.
#4
#5
Have checked the vacuum lines and part load breather as you suggested and cleaned the MAFS again for good measure. Problem remains. Tried another cold start today with the transmission in "Sport" mode and if anything that exacerbated the problem.
This prompted me to look up the "transmission surge" threads on the forum and found 3 Jaguar Technical Bulletins covering surge during warm up, harsh transmission shifts and transmission noise during gear shifts. All suggest software updates should fix these problems. I will get the car to a ZF transmission specialist (which may mean a trip to Sydney 220 km away) and see whether that leads to a solution. I wll keep you posted.
Thanks again for your help to date. Regards. Colin T. Bathurst NSW Australia
This prompted me to look up the "transmission surge" threads on the forum and found 3 Jaguar Technical Bulletins covering surge during warm up, harsh transmission shifts and transmission noise during gear shifts. All suggest software updates should fix these problems. I will get the car to a ZF transmission specialist (which may mean a trip to Sydney 220 km away) and see whether that leads to a solution. I wll keep you posted.
Thanks again for your help to date. Regards. Colin T. Bathurst NSW Australia
#6
Have checked the vacuum lines and part load breather as you suggested and cleaned the MAFS again for good measure. Problem remains. Tried another cold start today with the transmission in "Sport" mode and if anything that exacerbated the problem.
This prompted me to look up the "transmission surge" threads on the forum and found 3 Jaguar Technical Bulletins covering surge during warm up, harsh transmission shifts and transmission noise during gear shifts. All suggest software updates should fix these problems. I will get the car to a ZF transmission specialist (which may mean a trip to Sydney 220 km away) and see whether that leads to a solution. I wll keep you posted.
Thanks again for your help to date. Regards. Colin T. Bathurst NSW Australia
This prompted me to look up the "transmission surge" threads on the forum and found 3 Jaguar Technical Bulletins covering surge during warm up, harsh transmission shifts and transmission noise during gear shifts. All suggest software updates should fix these problems. I will get the car to a ZF transmission specialist (which may mean a trip to Sydney 220 km away) and see whether that leads to a solution. I wll keep you posted.
Thanks again for your help to date. Regards. Colin T. Bathurst NSW Australia
It's much easier to do this with a graphing scantool of course, but you can prove it with live data, too.
Good luck! Hopefully the repair per the bulletin with do it for you.
Cheers,
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colinturner (05-06-2011)
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