XJ6 & XJ12 Series I, II & III 1968-1992

Smooth idle -- possible or not?

 
  #1  
Old 01-19-2012, 02:36 AM
Senior Member
Thread Starter
Join Date: Jun 2009
Location: California
Posts: 192
Likes: 0
Received 2 Likes on 2 Posts
Default Smooth idle -- possible or not?

Since I'm new to my 87 XJ6, I'm wondering how smooth these engines idled when they were new?

I have recently replaced thermostat, CTS, MAF, plugs, cap, and rotor in order to pass the smog test. The engine now warms up fine and runs fine. All except for the idle which still bounces a bit too noticeably while at a stop light.

Next steps might be the fuel filter and possibly injector service. Another possibility is the throttle position sensor -- if this XJ has one. Sometimes a TPS will put out an unstable signal at idle as it wears out. In any case, I wanted some opinions just to make sure I'm covering all the bases.
 
  #2  
Old 01-19-2012, 06:27 AM
Senior Member
Join Date: Mar 2010
Location: S. Carolina, USA
Posts: 174
Received 14 Likes on 10 Posts
Default

I've got an '86 XJ6 so basically the same car as yours. I don't know if I'd say my idle is perfectly smooth yet, but one thing that helped me out was going through and thoroughly replacing all vacuum lines in the engine compartment. If this hasn't been done on your car the you are guaranteed to have some cracked hoses which let unwanted air into the mix.

Sending the fuel injectors is probably a good idea as well, that's my next step as well.

Good luck!

Eric
 
  #3  
Old 01-19-2012, 07:21 AM
Veteran Member
Join Date: Mar 2008
Location: Pacific Northwest USA
Posts: 20,160
Received 6,562 Likes on 4,864 Posts
Default

Originally Posted by e21pilot View Post
Since I'm new to my 87 XJ6, I'm wondering how smooth these engines idled when they were new?


Nobody remembers.

The choppy idle is an age-old bugaboo with these cars, though




Next steps might be the fuel filter and possibly injector service.


Professional injector has improved the idle on every car I've own



Another possibility is the throttle position sensor -- if this XJ has one.


Nope, it doesn't



In any case, I wanted some opinions just to make sure I'm covering all the bases.


Here's a great checklist from a guy who spent a couple years improving the idle quality of his Ser III

tipofmonth7 - Rough Idle Remedies for 4.2L FI Engines

Cheers
DD
 
  #4  
Old 01-19-2012, 12:00 PM
Senior Member
Join Date: Mar 2010
Location: S. Carolina, USA
Posts: 174
Received 14 Likes on 10 Posts
Default

I sent the injectors out, for my BMW 6 series, to a place called InjectorRX and waiting for them to get back this week. I'll let you know how they turn out.

Eric
 
  #5  
Old 01-20-2012, 02:44 AM
Senior Member
Thread Starter
Join Date: Jun 2009
Location: California
Posts: 192
Likes: 0
Received 2 Likes on 2 Posts
Default

Thanks for the tips and link. Is "Professional injector" a company that specializes in Jaguar injector service? I did this site: Jaguar Fuel Injector Service but he is pretty far away from me. Something in SF Bay area would be ideal.
 
  #6  
Old 01-20-2012, 08:57 AM
Veteran Member
Join Date: Mar 2008
Location: Pacific Northwest USA
Posts: 20,160
Received 6,562 Likes on 4,864 Posts
Default

Originally Posted by e21pilot View Post
Thanks for the tips and link. Is "Professional injector" a company that specializes in Jaguar injector service? I did this site: Jaguar Fuel Injector Service but he is pretty far away from me. Something in SF Bay area would be ideal.

Not Familiar with SF Bay Area so I'm no help.

I've used Jaguar Fuel Injector Servce several times....outstanding service.

Cheers
DD
 
  #7  
Old 01-24-2012, 09:46 AM
Member
Join Date: Apr 2008
Location: San Antonio, Tx
Posts: 35
Received 1 Like on 1 Post
Default

i also have a bit of a rough idle on my 84 xj6 and was wondering where i could get a diagram of the vacuum hoses for the 4.2. I fear i may have a hose missing and need a bit of reference to correct this.
 
  #8  
Old 01-24-2012, 11:08 AM
Veteran Member
Join Date: Mar 2008
Location: Pacific Northwest USA
Posts: 20,160
Received 6,562 Likes on 4,864 Posts
Default

Originally Posted by bert_vdp View Post
i also have a bit of a rough idle on my 84 xj6 and was wondering where i could get a diagram of the vacuum hoses for the 4.2. I fear i may have a hose missing and need a bit of reference to correct this.

http://www.jag-lovers.org/xjlovers/info/XJ6Vacuum.pdf

Cheers
DD
 
  #9  
Old 01-26-2012, 05:23 PM
Member
Join Date: Feb 2011
Location: Redwood City, California
Posts: 35
Likes: 0
Received 5 Likes on 5 Posts
Default

Rich - I remember it was always a struggle for San Jose British to get our cars to idle properly when they were new. I just had my injectors done by Jaguar Fuel Injection Service and their turn around time and service is great. I am still working on getting the idle to smooth out. Let me know if you want to take a look at my car to compare it.

Ryan
 
  #10  
Old 01-27-2012, 04:25 PM
Member
Join Date: Apr 2008
Location: San Antonio, Tx
Posts: 35
Received 1 Like on 1 Post
Default

thanks so much for this.
 
  #11  
Old 01-30-2012, 09:44 PM
Join Date: Jan 2012
Location: Newport Beach, California
Posts: 3,612
Received 1,149 Likes on 927 Posts
Default

While I'm no expert on the matter, I have owned several Series III XJ6s and getting them to idle smoothly can be both frustrating and time consuming.

Basically, the wonderful XK engine was never designed to run on such a lean mixture or to be encumbered with pollution-control equipment such as air injection. Add to that the higher operating temperatures required for control of nitrogen oxide pollutants and well, you get the picture!

I had reasonable success with ensuring ALL possible entry points for unmetered were eliminated. These included the vacuum hoses, of which there are many; the throttle housing spindle, which is made of brass and can wear unevenly over time and the oil dipstick tube seal. When the XK engine was designed, crankcase ventilation was not an issue, so things like the oil dipstick tube and oil filler cap were not required to hold pressure/vacuum.

I got my last 1985 XJ6 to run rather smoothly after paying close attention to the list above.

NBCat
 
  #12  
Old 02-04-2012, 04:22 AM
Senior Member
Thread Starter
Join Date: Jun 2009
Location: California
Posts: 192
Likes: 0
Received 2 Likes on 2 Posts
Default

It's a small start but I found that the rubber seal around the dipstick was cracked down one side. Not surprising considering its age.

I found a matching rubber stopper at the local hardware store, cut the center core with a sharpened piece of thin aluminum tube and just like that I had a good sealing dipstick once again.

I'll check the oil cap tomorrow and see if it has a gasket or not.

Not sure about the spindle in the throttle body. Is there a clever way of telling it is leaking without disassembling the throttle body?
 
  #13  
Old 02-04-2012, 08:37 AM
Join Date: Jan 2012
Location: Newport Beach, California
Posts: 3,612
Received 1,149 Likes on 927 Posts
Default Smooth idle -- possible or not?

Originally Posted by e21pilot View Post
...I'll check the oil cap tomorrow and see if it has a gasket or not...
It does have an O-ring type seal that may be perished from age or missing.

Originally Posted by e21pilot View Post
...Not sure about the spindle in the throttle body. Is there a clever way of telling it is leaking without disassembling the throttle body?
With the engine at idle, spray some carburettor cleaner around the throttle body and see if the idle speed changes. The spindle goes through from the connections with the throttle and down-shift cables to the position sensor on the other side. Be sure to spray around both those areas.

NBCat
 
  #14  
Old 02-18-2012, 08:53 PM
bbarcher's Avatar
Senior Member
Join Date: May 2009
Location: San Antonio, TX
Posts: 178
Received 15 Likes on 15 Posts
Default

A recent thread about intermittent idle stumbling and tachometer issues was resolved by replacing the distributor, vwtechnician posted that the new distributor improved the overall idle quality noticeably.

Also, you can order new dipstick seal and oil cap seal from the usual parts houses online.
 
 
Related Topics
Thread
Thread Starter
Forum
Replies
Last Post
bdboyle
XJ XJ8 / XJR ( X308 )
11
04-11-2019 11:50 AM
workworkwork
XJS ( X27 )
46
10-23-2015 10:26 AM
tomkilner
XJ XJ6 / XJR6 ( X300 )
16
10-09-2015 07:10 AM
Spazzzzzzzzzy
XJ40 ( XJ81 )
7
10-05-2015 04:05 PM
inactualis
XJ XJ8 / XJR ( X308 )
7
10-02-2015 11:13 AM

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 

Thread Tools
Search this Thread
Quick Reply: Smooth idle -- possible or not?


Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

© 2019 MH Sub I, LLC dba Internet Brands

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.
 
  • Ask a Question
    Get answers from community experts
Question Title:
Description:
Your question will be posted in: