Jaguar S Type Diesel: Rough Idle & Fuel System Fix Tips

Had similar symptoms on a 2008 Jaguar XJ diesel at 160000km. The rough idle and increased fuel consumption were clear signs of fuel system issues. The cold start was particularly problematic, taking several attempts to get the engine running. After diagnostics, it turned out the fuel filter heater wiring harness had corroded connection points, causing intermittent electrical contact. This affected fuel efficiency and created the rough idle symptoms. The repair involved replacing the wiring harness assembly and the fuel filter as a preventive measure. The job was relatively straightforward but required specific diagnostic equipment to properly test the fuel heater circuit. The repair was essential since a malfunctioning fuel heater can lead to fuel gelling in cold weather and potential fuel system damage. A proper fix should include: Full diagnostic scan, Fuel filter replacement, testing fuel heater circuit, checking and replacing damaged wiring, Verifying proper fuel pressure This is not a repair to postpone, as continued operation with a faulty fuel heater can cause more extensive fuel system damage and leave you stranded in cold weather.

Thanks for sharing your experience. My S Type had almost identical issues. The rough idle and cold start problems were really frustrating, especially when the fuel consumption kept rising. Did you remember the total repair cost for your XJ? My mechanic fixed the wiring and replaced both the fuel filter and heater assembly, but wondering if your bill was similar. Also curious if you had any other fuel system problems pop up since the repair? The diesel engine on mine has been running smoothly after the fix, but always good to know what to watch out for.

Good news to share, got my Jaguar XJ back from the mechanic and the fuel filter heater issue was completely resolved for just 95€. They found a faulty cable connection that was causing all those fuel system problems. Much cheaper than expected and no need for a complete heater assembly replacement. The fix has made a huge difference, no more rough idling or cold start issues. Fuel efficiency is back to normal and the engine runs perfectly smooth now. It has been about 6 months since the repair and no other fuel system related problems have shown up. For preventive maintenance, the mechanic recommended regular fuel filter changes every 60000km and keeping an eye on any changes in engine performance or fuel consumption. Early detection of fuel system issues can prevent more costly repairs down the line. Worth noting that a proper diagnosis saved a lot of money here, what initially seemed like a major fuel system problem turned out to be just a bad electrical connection. Getting a second opinion definitely paid off in this case.

Thanks for the helpful insights. I finally got my S Type fixed last week and wanted to share the outcome. Took it to a different mechanic who actually found the issue without trying to upsell unnecessary repairs. The fault turned out to be a combination of a clogged fuel filter and corroded wiring to the heater element. Total repair came to 180€ including parts and labor. They replaced the filter, repaired the wiring harness, and did a full system pressure test to confirm everything was working properly. The diesel engine runs like new now, no more rough idle issues and fuel efficiency is back to normal. Cold starts are smooth and the check engine light has stayed off. Really glad I got a second opinion instead of paying for expensive repairs I didnt need. Will definitely stick with regular filter replacements from now on. The mechanic showed me how dirty the old filter was and explained how it was affecting the fuel system. Lesson learned about not skipping maintenance intervals.