difficult to start
 

I have a 1990 300sl and I must crank it several times to start and it runs poorly until it warms up.

Check the usual suspects:

Plugs
Wires
Cap
Rotor
Vacuum leaks (anywhere between MAS and intake valves.

Could be a bad or dirty MAS, although that would affect warm running too.

The problem is that you are too lean at start and warmup before the computer goes into closed loop mode and adjusts fuel delivery to actual oxygen content of the exhaust. the O2 sensor has to warm up before this can happen, so once it's hot, you get pretty much normal running -- but I bet it's MUCH better once you get the problem fixed.

If it "chuggs" or knocks while attempting to start hot, you have carbon tracking in the distributor cap and need to replace the camshaft seal, its letting oil into the cap, and that will sooner or later, usually sooner, cause carbon tracks to form between the posts, causing spark to show up at the cylinders at inappropriate times.

The vacuum will drive you nuts -- my BIL bought a nice BMW and then had fits with it being hard to start, stalling on takeoff (manny tranny), rough running, poor acceleration, etc.

Turned out to be a crack in the plastic air ducting between MAS and throttle body. Got it fixed, runs like a Bimmer should.

Peter

I'd also consider changing the rear fuel accumulator located near the fuel pumps, hear is the link:
http://catalog.worldpac.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=25R0QM1R225R0QMVNV&year=1990&make=MB&model=300-SL-001&category=E&part=Fuel+Accumulator

I don't have that car, and I don't know your skill level or what you have tried already, but an obvious area to also check is the cold start start system, valve, injector, timer etc. The other 2 posts make good points also. And of course do some searches.

Psfred where have you been????

Mike

Hey Mike.

Been busy and haven't had to work on the cars since the head gasket on the 300D which did not fix it (still need to get the "reworked" head properly done over).

I don't think there is a cold start valve on LH-Jet. Could be wrong. Bad accumulator will cause hard starts though, as it takes a while to fill.

Peter

Uhhhh, Peter, I think we have a little misunderstanding... We are not here to help fix YOUR car, you are supposed to help us fix OURS!!!

Mike

whit2004, I'm waiting for your feedback :)