380 SL Hiccups

[DaimlerChrysler]

My '84 380 SL runs fine when cold or when it's cold outside. When warm (85 degrees centigrade...the engine , not the ambient temp) it tends to hiccup when at a stop light about once every10 seconds or so.I've replaced the distributor cap and rotor, new spark plugs and wires and air filter.The idle control module had to be replaced shortly after I bought the car. I'm afraid to take it to the dealer..the last time I took it in for an oil change I asked them to check the exhaust while it was up on the rack, they did and charged me $45 in addition to the $65 oil change!


What do I do next?

[LOWMILE]

I would change the fuel filter, Benz charge's about twenty bucks I have not priced them here at this site chance are even cheaper!
If you want to get real cheap take out the stock one and frankenstein an aftermarket one on just to see if this help's. I would also take some propane or carb cleaner and check for vaccum leaks. These car's are all about vacuum. The rubber o-rings around injector's can give you a hiccup. When you had cap and rotor replaced did the hiccup get better or worse stay the same? Hope this help's hiccups can make you nut's. Don't ask me how I know.

[Darrell Woods]

Using Carb cleaner, how do you check for vacuum leaks? Spray it on the hose, and if so, look for what indication of a leak?

[LOWMILE]

With engine idleing spray a little on suspect vacuum hose. If idle slows or lopes a little change that hose and move on to another one. Some guy's use propane. Try spraying around the injectors.Be careful! Another good trick is at night take some windex...be careful this is also flammable! Spray the windex on the sparkplug wires and distributor cap. Look closely for spark's arcing to ground! Be careful windex is flammable! This can also cause a hiccup. By the way did you use platinum spark plugs? You want to use copper core plug's. These older fuel injected cars desire a fatter juicy spark. The plats give a hot but thin spark. The rich idle circuits tend to blow out these thinner sparks, I learned the hard way!
Good luck
Ernie

[Darrell Woods]

Thanks for the reply. I'll give it a shot, since I really think some or all of my problem could be vacuum related.

[ctaylor738]

The most common sources of vacuum leaks are around the injectors and the idle hoses. I was advised to replace every rubber hose on top of the engine, plus the injector holders, and the collars that fit into the holders, and to pull the intake manifold off and replace the gaskets between the top and bottom half and well as the manifold-head gaskets.

While all this is apart, I am also going to replace the injectors.

This to fix a similar but worse hot idle problem.