• Advertisement
Xclusively Jaguar
SNG Barratt
David Marks Garages
Make a donation to XJ40.com

Xj81 Running Rough on idle

panarabica
Posts: 129
Joined: Sun Apr 19, 2015 7:00 pm

Xj81 Running Rough on idle

Postby panarabica » Mon Jun 24, 2019 8:46 pm

My 94 Xj81 just got motd after sitting nearly a year. The car was in good running order when parked but has developed over time a habit of stalling when idle, and often only running at 300-400 rpm when cold. Once warm it’s all good, and the car idles at 620 rpm. No VCM code. Now the check engine light has come on, and I have done a bit of research.
A culprit seems to be the o2 sensors.i cannot find any ,material on how to replace those on a xj81 let alone how many there are. 2 or 4? How complicated is it to change those?
After having spent 110€ on trying to gas up my ac system, and having a leak on the compressor I am not in the mood to experiment to much with spare parts.
I know there can be plenty of other causes to the problem, but I think the o2 sensors are a good guess.

Any thoughts?

Robert
- Jaguar DD6 MY'93
- Mercedes S500 Lorinser MY'99
- Mercedes E350 MY 17
- Mercedes S300 MY '67
- Mercedes SL280 MY`94
- Mercedes C220 MY'15

Walker
Snr Member
Posts: 235
Joined: Fri May 01, 2015 8:10 am
Location: Inverness

Re: Xj81 Running Rough on idle

Postby Walker » Tue Jun 25, 2019 9:51 am

My understanding of the o2 sensor is that they only come into effect when the exhaust temp is within a certain range. My V12 knowledge is next to Nil, however despite they're complexity there are a few members on here who know them well, hang tight for their attention!
Kingfisher Blue '40 1993 3.2S #690760 L399GYP
Sapphire Blue '40 1994 Gold 3.2 #702107 L9CYD
Previous 1994 X300 3.2 Manual

naki_k
Super Moderator
Posts: 28341
Joined: Sun Feb 21, 2010 9:25 pm
Location: Kirton, nr Boston, Lincolnshire

Re: Xj81 Running Rough on idle

Postby naki_k » Tue Jun 25, 2019 11:23 am

Clearly the revs should be much higher when cold. 1100-1200rpm. I would think the Extra Air Valve is not working/ stuck?
New parts for this are expensive. Used are v scarce/ expensive. I did a little post on them. With contributions from other members showing a refurbishing route, for a lower cost.

If there’s no VCM code showing it’s less likely to be Oxygen sensors. You can manually measure their resistance values (search for the figures online to compare them to).
88 3.6 XJ6 PDH/CEM
90 Range Rover Vogue SE 3.9 V8 LPG
91 4.0 XJ6 Manual
92 4.0 XJR Manual
92 4.0 XJR
93 3.2s - 4.0 Manual conv
93 4.0 Sovereign
93 6.0 XJ81 DD6 x2
93 6.0 XJ81 XJ12
94 4.0 XJR
94 4.0 Daimler
96 4.0 X306 XJR
96 4.0 X300 D6
97 4.0 X300 Sport Manual
2000 LR Discovery ES TD5 A
Breaking 40/ 300

newyankee
Posts: 61
Joined: Mon Oct 06, 2014 7:32 am
Location: Hamburg, Germany

Re: Xj81 Running Rough on idle

Postby newyankee » Wed Jun 26, 2019 8:50 am

620 rpm is too low for a warm engine. Spec is 750 in Park/Neutral and 650 in D.

I would definitely check the AAV first, adjust idle screw to above values. If this doesn't work, clean AAV. Only if the AAV then doesn't work to get an acceptable idle on a cold engine, I would proceed further. On well used AAVs idle is usually higher when cold, but that's due to the degrading wax bulb.

As an additional measure, I would check both throttles for clearance and clean them.
--
1994 XJ12
1964 MkII 4.0 project
1968 TR5
2016 RRS SDV8 4.4
2013 Touareg 4.2 TDI totaled

panarabica
Posts: 129
Joined: Sun Apr 19, 2015 7:00 pm

Re: Xj81 Running Rough on idle

Postby panarabica » Wed Jun 26, 2019 1:54 pm

Thanks for the reply's on my idle issues. Having read through several posts, I understand that the AAV is a hot candidate for my problems. As i understand it can be cleaned, as per a procedure mentioned in a post by leo-denmark. Now I am a bit confused as I read that there is a wax/oil in the valve that operates at certain temperatures. There is no mention in the cleaning procedure of adding any oil.
Has anyone done the cleaning procedure and has a working AAV?
- Jaguar DD6 MY'93
- Mercedes S500 Lorinser MY'99
- Mercedes E350 MY 17
- Mercedes S300 MY '67
- Mercedes SL280 MY`94
- Mercedes C220 MY'15

naki_k
Super Moderator
Posts: 28341
Joined: Sun Feb 21, 2010 9:25 pm
Location: Kirton, nr Boston, Lincolnshire

Re: Xj81 Running Rough on idle

Postby naki_k » Wed Jun 26, 2019 6:52 pm

Did you read through this already?

viewtopic.php?f=20&t=998942&hilit=Extra+air+valve
88 3.6 XJ6 PDH/CEM
90 Range Rover Vogue SE 3.9 V8 LPG
91 4.0 XJ6 Manual
92 4.0 XJR Manual
92 4.0 XJR
93 3.2s - 4.0 Manual conv
93 4.0 Sovereign
93 6.0 XJ81 DD6 x2
93 6.0 XJ81 XJ12
94 4.0 XJR
94 4.0 Daimler
96 4.0 X306 XJR
96 4.0 X300 D6
97 4.0 X300 Sport Manual
2000 LR Discovery ES TD5 A
Breaking 40/ 300

panarabica
Posts: 129
Joined: Sun Apr 19, 2015 7:00 pm

Re: Xj81 Running Rough on idle

Postby panarabica » Tue Jul 02, 2019 1:37 pm

Yes I did. But still not sure about the topic of the wax bulb. Maybe I am just misunderstanding this. Had the car running more or less normal, without throwing an error code. Then I let it idle for .5 min, and the error is back on.
- Jaguar DD6 MY'93
- Mercedes S500 Lorinser MY'99
- Mercedes E350 MY 17
- Mercedes S300 MY '67
- Mercedes SL280 MY`94
- Mercedes C220 MY'15

newyankee
Posts: 61
Joined: Mon Oct 06, 2014 7:32 am
Location: Hamburg, Germany

Re: Xj81 Running Rough on idle

Postby newyankee » Tue Jul 02, 2019 2:00 pm

Low or high idle due to a poorly working AAV doesn't throw VCM error codes or a CEL. If the CEL comes on, there should be an error code. You will need to read the code.

If you have e.g. dripping injectors causing a rich mixture, failing O2 sensor(s) you will have error codes. Check for those first. Secondly, I would probably take a look at all spark plugs to see if any are wet, black, sooted. You might have ignition issues somewhere. A single cylinder not firing will also cause the idle to drop.
--
1994 XJ12
1964 MkII 4.0 project
1968 TR5
2016 RRS SDV8 4.4
2013 Touareg 4.2 TDI totaled

panarabica
Posts: 129
Joined: Sun Apr 19, 2015 7:00 pm

Re: Xj81 Running Rough on idle

Postby panarabica » Tue Jul 09, 2019 2:05 pm

Having read the posts, I will go forward with following measures:

- Check that all ignition leads are mounted correctly and are properly attached
- Remove all spark plugs and and throw some new ones in
- Double check that the dizzy cap is clean and dry (replaced it before it went into storage)

and will see how the beast runs then. Sometimes it's the basic stuff that solves the problems. The car has also decided to not throw the check engine light any more, but she is still not running a 100% smooth as I would expect on a V12.

Rob
- Jaguar DD6 MY'93
- Mercedes S500 Lorinser MY'99
- Mercedes E350 MY 17
- Mercedes S300 MY '67
- Mercedes SL280 MY`94
- Mercedes C220 MY'15