Running Rough at Idle

[sublettd]

The wife and I were out today shopping. Got back in the SL and when I started it, it sounded like it backfired through the fuel distributor. (Don't even know if this is possible or not with the CIS, but that is what it sounded like.) Shut it off, restarted and it idled very rough, but kept running. On the drive back home I idled it up to about 1000RPM at the traffic lights because I was concerned it would die and possibly not restart.

Got back to the house and I started swapping spare parts that I keep on hand--idle speed control valve, then the idle speed control unit behind the glove box and, finally, the ignition control unit. Problem didn't get any better, but didn't get any worse either.

The idle speed control unit is such a pain to get to that I left the replacment one in as well as the replacement ignition control unit. However, I reinstalled the initial idle speed control valve. Interestingly, the idle dropped from ~750rpm to ~500rpm, but still missing and idling rough.

The car has been stumbling on start-up for awhile now, but after a few seconds smoothed out nicely. Reading other threads here recently, it seems the car might need new injector seals.

Last weekend I replaced the spark plugs with W9DC, which was what was in it. First couple starts after the plugs were replaced were smooth as silk. Then, the stumbling start began again. When I ordered the plugs, I went ahead and ordered injector seals, o-rings and injector holders(???), expecting that with 136,000 miles it was time to do this. My previous mechanic replaced the plug wires, distributor cap and rotor. He didn't want to have to pull the battery and battery tray on the right side to replace the plugs, so he didn't. That's why I replaced the plugs myself.

The problem I am up against is both of the decent independent mechanics that were in the area are no longer here. One moved and the other retired. The guy I am using now is pretty good, but is not a MB specialist. I dread the prospect of taking the car to the dealer, so I'm looking for suggestions.

I also have a spare kickdown switch, which I understand is (or contains) the fuel pump relay. Is this a possible fix? I'll likely try this as a possiblity tomorrow regardless.

Suggestions appreciated!

[dpetryk]

Sounds like you have a large vacuum leak. A backfire could have poped off a hose somewhere. Check the auxillary air lines and everywhere that vacuum might develop a leak.

[sublettd]

Hadn't considered that possibility. Thanks.

[sublettd]

Took a drop cord light and went over the engine. Sure enough, there was a vacuum connection off on the right side and next to the fuel distributor. Put it back on and the rough/missing idle smoothed out. However, rev the engine up and let off the accelerator and it nearly dies. Most of the time it catches before it actually dies, but occasionally dies. So, I'm going to put the first idle speed control unit back on and see if that helps. If not, I'll put the original Ignition Control Unit back on as well. Seem to be in a lot better shape at present than I was originally.

Appreciate the tip!

[sublettd]

Well, looks like I am back in pretty good shape. Reinstalled the original Idle Speed Control Unit and that solved the problem with it dying. Still plan to get it in this week to replace the injector seals, etc.

Thanks again.