Date registered: Sep 2017
Vehicle: 1973 450SL
Location: Seabrook, TX
Mentioned: 0 Post(s)
Quoted: 33 Post(s)
450SL with odd but specific starting issue:
1973 450SL D-JET - Fuel pressure great at 30PSI at injectors (correct PSI for this model). Last time I checked a few months ago, it held fuel system pressure just fine after car is shut off.
I little background regarding the idle and the AAV (auxiliary air valve). When we first bought the car last summer, it cold idled at 1600-1700 rpms. Even when warm it still idled high at 1000 rpms. I tapped down the AAV very carefully with a hammer. After tapping down the AAV, it cold idled at 1100 or so (too low?) then 600-700 when warm (we put the car in the shop shortly after so did not have time to test under different driving conditions).
Now that we have it out of the shop and driving again (details of driveline repair in previous post) we are having idle and starting issues under certain circumstances.
In the morning the ambient temperature is about 55°F. The car starts right up and idles at 1000 rpm cold (too low?). My wife then drives no more than 15 minutes to a park and ride to catch a carpool to work. When she comes back to the car after work (about 8-9 hrs) with an ambient temp of about 75°F, the car takes many tries to get it started. And when it does fire up it fumbles up to a smooth idle but is only idling at 500 rpms, cold. After that, its fine. Idles smooth, runs great and you can start it right back up when she gets in the driveway. Even a few hours later it still starts right up.
The only time the hard start happens is after she tries to start the car after work (8-9hrs after being parked). I also think I have the idle adjusted out further than spec just to keep the idle up when warm (i could be wrong).
This is confusing because its starts fine cold, its starts fine when warm if you start it within a couple of hours after shutting it down. Only hard time starting is after work. Could it be that the AAV is sticking in the "warmed up" closed position? Maybe since its 55°F in the morning the AAV opens back up and the cold start valve kicks in, but the 75°F in the afternoon is keeping the AAV in the closed position? Sticky AAV? Any other things I should check out?
Could I have tapped down the AAV too far? I tapped it down to where the lip of the valve is flush with the housing. It was sticking out of the housing about 1/8 inch.
To be sure, tapping down the AAV lowers the RPM and pulling it up raises the idle, correct?
Any help is appreciated.