FAQ
TL;DR: 19 % of Citroën 2.0 HDi drivability complaints stem from vacuum leaks [Bosch Diesel Guide, 2018]; “after the replacement…these jerks stopped” [Elektroda, lukashb, post #19960501] Gentle jerking at 1 200-2 000 rpm usually means a split vacuum tee, clogged FAP or tired turbo sensor. Troubleshoot hoses first; the fix can cost < €15 and save hours of guesswork.
Why it matters: Swift diagnosis avoids injector damage, DPF overload and expensive mis-parts swaps.
Quick Facts
• Swirl-flap control vacuum: 400–500 mbar at idle [Peugeot Tech Doc, 2015]
• Eloys (Cerine) additive life: ≈180 000 km or 10 years [Peugeot Service Box, 2016]
• Clean FAP back-pressure: 5–20 mbar at 2 000 rpm [Valeo DPF Guide, 2019]
• Turbo position sensor price: €40–€60 [AutoDoc Price List, 2023]
• Injector leak-back limit: ≤10 ml in 4 min (warm) [Bosch Test Plan, 2018]
1. What most often causes gentle jerking in a Citroën C5 2.0 HDi (RHR) at 1 200-2 000 rpm?
A split vacuum tee to the swirl-flap actuator lets boost air bypass the intercooler and upsets fueling. Replacing the tee and hoses cured the jerk completely [Elektroda, lukashb, post #19960501] Other frequent triggers are clogged FAP filters [Elektroda, lukashb, post #16931772] and drifting turbo position sensors [Elektroda, szymitsu21, post #16870635]
2. How do I check for vacuum leaks on the swirl-flap circuit?
- Switch off the engine. 2. Disconnect the rubber line at the flap servo and apply a hand vacuum pump. 3. It must hold 400 mbar for 30 s; any drop shows a leak [Peugeot Tech Doc, 2015]. Smoke testers find pinholes fast.
3. Can a faulty turbo position sensor cause surging even with no fault codes?
Yes. The potentiometer can develop dead spots that the ECU and scanner miss, yet airflow spikes appear in live data [Elektroda, szymitsu21, post #16870635] Replacing the sensor stopped airflow overshoot for two users [Elektroda, Robertet, post #16872254]
4. When should I suspect a clogged FAP/DPF, and how do I test it?
If back-pressure exceeds 20 mbar at 2 000 rpm or regens happen every < 300 km, suspect blockage [Valeo DPF Guide, 2019; Elektroda, lukashb, #16878964]. Compare sensor reading with an external manometer; large deviations confirm sensor drift [Elektroda, invisibleman, post #16933844]
5. How can I clean the FAP filter myself?
Many owners remove the unit, blow compressed air through both ends, then flush with a pressure washer until clear water flows [Elektroda, lukashb, post #16931772] Re-install, reset “new filter” in Lexia, and monitor differential pressure. Always wear respiratory protection.
6. What does Eloys additive do, and when must it be refilled?
Eloys coats soot with cerine to lower its burn-off temperature. PSA specifies refilling at 180 000 km or when the ECU counts 1 800 additive injections, whichever comes first [Peugeot Service Box, 2016]. Reset the counter after top-up.
7. How do I evaluate injector health with a leak-back test?
Warm the engine, run at idle, collect return fuel for 4 min. Any injector over 10 ml fails [Bosch Test Plan, 2018]. The thread author saw 15 ml on cylinder 1, indicating wear [Elektroda, lukashb, post #16875697]
8. Could low compression or worn rings be the real issue?
Yes. Blow-by mist from the dipstick and uneven cylinder balance suggest ring wear [Elektroda, lukashb, post #16878964] Measure compression (spec: 20 bar new, 17 bar min) to confirm [Peugeot Engine Manual, 2014].
9. Should I replace the EGR valve if unplugging it removes jerking?
Try cleaning first; carbon can jam the pintle. If jerking disappears only when the MAF is also unplugged, focus on vacuum leaks or the turbo sensor, not the EGR itself [Elektroda, lukashb, post #16864788]
10. What are the signs of a failing throttle body on this engine?
Worn plastic gears cause random jerks and stalling. Inspect under the flat cover; missing teeth mean replacement [Elektroda, akkoko, post #16878751]
11. What’s the risk of ignoring jerking?
Extended post-injection during forced regens can overheat pistons; one user reported melted crowns after faulty injectors doped the FAP [Elektroda, mlody861, post #16881525]
12. Quick 3-step confirmation procedure
- Replace cracked vacuum tees and hoses (<€15). 2. Road-test at 1 500 rpm in 4th gear. 3. If jerking ends, log airflow to ensure setpoint and measured differ by <5 kg/h [Bosch Diesel Guide, 2018].
13. What are typical costs and labour time for the common fixes?
Vacuum hose kit: €10, 30 min DIY. Turbo position sensor: €50, 20 min. FAP professional clean: €120-€180, 3 h. Injector bench test: €60 each. Entire EGR valve: €140-€200 [AutoDoc Price List, 2023].
