I'm having a problem that's been very difficult to pinpoint so far, hoping maybe someone sees this as a telltale sign of something specific!

I drive a 1987 300E, 200xxx miles. A couple months ago, the problems started. When I first started the car in the morning and drove off, occasionally i'd get this stuttering feeling when I tried to accelerate, like I was putting my foot down but the car wasn't really listening. Actually it seemed to go a little slower and shakier when I was accelerating. Once I got the engine up to temp it was fine.

If I leave the car in park, it idles nicely. This problem oooonly seems to happen with your foot on the accelerator. I can duplicate this by leaving the car in park and revving the engine. When moving, the car just sort of crawls along for a few seconds, and then all of a sudden the acceleration kicks in and you zoom away. There's no clunking or bumping or specific noises when this happens, it almost feels like there's something stuck in the line and then it gets forced out. (not that that's got anything to do with what's wrong, but that's what it feels like!)

When the car started having problems, it was very intermittent and only for a few minutes after I started driving. It was also 90+ degrees most of the time. As it got colder, my problems became a more and more frequent. Originally, I also heard the engine misfiring when it was stuttering.

A couple of weeks ago, I gave in and took the car to a shop. Right off they pulled the plugs, which were totally black, and also the wires which were cracked. These were just replaced in June! They told me the fuel mixture was too rich and caused the plugs to blacken. The tech did some distribution adjustments and put in new Bosch plugs and wires.

When I got the car back, it idled perfectly. Takes a little longer to start, but usually goes on the first try if I give it a little gas. However, the stuttering is still there!

Not only is it still there, but now it occasionally pokes its head out when the engine is warm. This usually occurs when I am sitting at a stoplight and accelerate from a full start. The car creeps along and shakes and I have to take my foot off the accelerator and put it back down to try and get the car to move.

I took it back to the shop again, and they did more adjusting. When I first got it back this time, I thought the problem was taken care of. However hours later it stuttered - just once.

That was a week ago, and every day this stuttering becomes a little bit more frequent. I think something is going bad, I just need to figure out what! It's very scary going that slow through an intersection with angry people behind you, and even worse trying to turn into traffic without a signal. Today was the absolute worst.. not once, but twice!! I was at stoplights and when it turned green and I gave the car gas, it shook and moved a little bit and then stalled out, with all the warning lights on and all that. Luckily it started up again okay and I only had angry people to deal with behind me.

I may take the car back to the shop tomorrow, but i'm hoping for some opinions first before I get caught in the endless spiral of trying to fix the problem with random parts. Any help is appreciated!

 

Very hard to tell from here ,have they checked fuel pressure? have they checked all vacuum lines?
Have they checked the cam sensor and crank sensor and the distributor?My vote and it seems common on the 300E crankshaft position sensor.Go to a different shop,this one is tossing in parts and trying to see what works instead of correctly diagnosing the problem.
part at www.autohausaz.com about 40 bucks the last one I did on a friends 94
get a better shop,post your question over on mbworld.org 300 E section as well,great following over there.
ohlord

 

azautohaus is nearby to me, is the crankshaft sensor a reasonable DIY? At $40, it's worth replacing just on suspicion..

 

My problem when I had these symptoms was
1. The battery was almost dead.
2. The MAF oxygen sensor in the air intake had to be replaced.

If the battery is old, replace it. It used to be that if a car could be started, the electric power was then ok. Not so with these cars. If the computer senses that the voltage is low, it signals the car to shut down.

 

As Ohlord has said it difficult to diagnose from here.
A process of careful elimination is required.
Firstly start with the low cost stuff.
Is normal servicing up to date. Filters plugs etc. OK.
Next, Fuel pressure correct?
Battery voltage correct? 14+v at 2000 revs? MB's are sensitive to battery voltage but since the car cranks and restarts I don't think this is your problem. 14v will confirm that all is OK.

My concern is the black plugs.
OK its running rich but if after a good run (avoiding "spluttering" you still have black plugs I would ask myself why. Suspect it has nothing to do with the plugs or the leads since these have been changed out anyway.

200k. Wonder what the compression pressures are but the car wouldn't idle well if these were incorrect. Anyway a low cost test.

So either the "spark" is not occurring...the crankshaft sensor being a likely cause" or the fuelling is totally out.
However if the car idles OK it is surprising that the fuelling is rich at highway speed. Usual symptom is weak at highway speed and is caused by the Mass Airflow meter/sensor but I think not in this case.

Not sure what level of diagnostics this car has but 97 must have at least O2 sensors so need to access whatever the output is from these. Codes will be helpful in supporting or shooting down diagnosis to date.

Does the Check Engine Light come on when you turn the ignition on (i.e. is the bulb working) and has it come on whilst you are driving or is it on all the time? the light comes on when a fault develops that impacts emission legislation.

Do the basic test stuff first including getting the codes before you throw lots of money at the car. the Crank sensor being relatively low cost is worth the risk if you believe in luck!

Stuart