My 2004 XJ8 has an erratic idle. Mostly the idle is smooth, but when I rev it, it takes some time for the idle to settle.

The rpms are very low, then picks up, then very low again in a cycle. Then settles to normal as mentioned after a while.

I see the figures from the mass flow sensor is fluctulating, but whether it is the sensor or something else I am a bit unsure of.

What can it be? Any suggestions? How do I diagnose if faulty MAF?


br Martin

 

What year is your XJ8? Vacuum leak?

 

It is a 2004 - 3.5

 

Without checking for codes it's hard to say?
The car is now 20+ years old. All the rubber coolant and vacuum lines are at the end of their life.
How many miles? Have the plugs and coils been changed?
When was the fuel filter last changed?
Air filters changed?

Better to stop trying to figure it out and let the car guide you with what codes it has.
Next? What code reader do you have? Be aware that Jaguar has a very complicated system called SDD that the factory guys use.
.
.
.

 

No fault codes. Plan to change the fuel filter. Plugs and coils - do not know, but on my list. I have not owned the car for that long.

 

V6?! Is it x300 or is it x350? I do not remember if x350 had V6 in them.
Any way, Cilbrath has given a good advise: follow the codes. With no codes you need very experienced tech to be able to diagnose following 'unmanifested' symptoms.
Good luck!

 

The 3.5L is a smaller version of the 4.2L V-8 but I don't think they were sold in the US?
.
.
.

 

Nope, the U.S gets the 4.2L V8 only; the 3.5L V8, 3.0L V6 and 2.7L TDvi engine are exclusive to other markets.

And yes, the 3.5L V8 is the smaller brother to the 4.2L V8, both should pretty much be the same except for displacement

 

Cleaned my MAF's. CRC has a bespoke spray for it. Problem persisted. New ones from China worked a treat.

Replaced both PCV valves, new caps included in the inexpensive kit.


'Worst case.." and hope it ain't:

- Leaking head gasket. (now proven, here... overheat damage, off they must come...)

- Jumped time / faulty VVT. (chains are overdue, might not YET have jumped a cog)

- Deteriorating valves no longer fully sealing. (not yet known)

- PCV system parts perishing (already addressed, here.)

You'll benefit from:

- compression and leak-down tests,
- inspecting oil and coolant for cross-contamination
- pressure/vacuum PCV/Evap and cooling system tests
- sniffing coolant for Carbon Monoxide (very cheap kit and colour-indicating fluid for that),
- better code scanner work.

An endoscope peek into each sparking-plug hole, ahead + side-view probe, is more than just "useful", can be an outright revelation that pays for the 'scope in one go.