I have a euro engine 117.961. The car operates very well, normal hot and cold starts, etc. Complaint is poor mileage, getting 13.0 MPG (at best) in city over many many months. Other complaint is that idle RPM falls below normal when outside temp. hits 78 deg. + with A/C on or in slow traffic.

Odometer is accurate. Electrical side is proper from coil to plugs. Timing is set at 30 deg. BTDC @ 3000 RPM with vacuum advance plugged. CO reading at 869 RPM is 0.43%. HC is 63 PPM. (No cat.) Cam timing is dead on. System pressure is 85 bar. Control pressure is 21 bar cold and 52 bar warm. Leakdown is 44 bar after 10 min. and 42 bar after 20 min. Water temp. is in 80 to 90 deg C. range. Rebuilt fuel distributor, no internal leaks. All injectors have good spray, no leaks. Cold start valve does not leak.

I recently diagnosed that vacuum advance diaphram was faulty. Bought new one through PartsShop and thought this was going to be the cure. Unfortunately not.

Pressure tests do not seem to suggest problems with warm up regulator or fuel pressure dash pot. Any suggestions besides just living with the problem?

Try a bit more timing, 34deg total should help. Also running just a bit richer .50-.75% co. US 500SEL's were EPA rated at 14mpg city.

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