Hello all,

I've noticed in the morning car starts and runs fine, however, after the engine is warmed up and I've been driving for an hour or longer, the vehicle can no longer idle properly and shakes terribly. It idles fine for the first 30-40 minutes.

It's also getting worse by the week. I've been reading quite a bit that the lift pump can cause this, however, I don't want to just throw money at it. The vehicle is fine at highway speeds, I can go 140km/h-180km/h fine so this just affects idling. It also fires right up on the first crank in the morning. Some details are below on the vehicle. Let me know your thoughts before I start replacing parts and thanks for reading this.

Other notes: I noticed ticking at idle, almost like valve ticking from low fuel pressure in the middle number 3 cylinder. If I swap injectors, the tick does not go away or move with the injector, so my guess is that it's the pump? Perhaps due to lack of fuel pressure?

Mileage - 450,000-500,000KM

Rear Tank Filter - I doubt this is it as I have no issues at high speeds but I can try replacing, it is original.

Lift Pump - is original and not leaking. I don't see any air bubbles in the system at all

Fuel System - well maintained, only quality diesel used and filters replaced often

Valve Adjustment - just done and to spec

Timing - not much timing chain stretch at all. It is original.

Compression - 320-370 on all cylinders.

Overflow valve on injection pump - I've adjusted this spring to 27mm from 22 as per the factory manual

Rack Damper (Idle Stabilizer on injection Pump) - This is original. Yes I know. I will replace but there's no way this can cause this much of a idle issue. Right? lol

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1976 Mercedes 240D (Sold)
1985 Mercedes 300D Turbo Diesel: 500,000KM
1986 Mercedes 300E (Sold)
1988 Mercedes 300E (Sold)
2002 Mercedes C240 (Sold)
2008 Mercedes C350 4matic

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