Hi I want to get a bit more power from my 1989 300SEL , where would be the best places to start? the engine is completely stock and pretty low milage .. runs very smooth but its a bit slow off the mark and im relatively new to mercedes altogether , seems like this is the best place to ask, thanks!

also it is sagging in the rear the previous owner told me that it was an air suspension system and it just needed a new valve or something?

The 6 cylinder W126's have stupid gearing, take off in 2nd gear, and have the cam set up for RPM rather than low down grunt. They're as slow to 60mph as the diesels as a result.

The self-leveling suspension was an option and is rare on the 6 cylinder cars. It is hydraulic and has an extra fluid tank in the engine bay. You know if you have this by looking at the rear suspension, if you have standard springs and shocks, you don't have it. If the shocks are hydraulic rams with hoses going to them, you have the SLS system.

The regular long-wheelbase cars had springs that would sag in the rear as they age and make it look like the rear is loaded up with concrete. The fix is to replace the subframe mounts, differential mount, and rear springs with the "HD" version which is slightly stiffer.

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Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Confirm that the duty cycle is adjusted properly on the fuel injection. If you put the gear selector in L and then back to D it should give a first gear start.

Very nice cars...good luck!!!

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

if your in a communist state,or county, with tailpipe emissions,buy another vehicle.
For maybe once and a blue moon,destroying some asian econo box crap. $500 nitrous oxide wet system does well,100 hp shot,no special spark plugs,or timing needed.About $6.00 a shot to see,some traitor young punk,in asian crap,get burnt.
Next www.turbobandit.com m103 kit,over 600hp of beautiful joy. I would take a step further,to add water injection,for long motor life. W126 diff mount sag over time,I hammered a wooden wedge in mine

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1999 w140, quit voting to old, and to old to fight, a god damned veteran