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.

 

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

 

Nobody remembers.

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






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





Nope, it doesn't





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

 

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

 

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

 

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

 

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

 

thanks so much for this.

 

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

 

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?

 

It does have an O-ring type seal that may be perished from age or missing.

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

 

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.