Acceleration... resistance?
 

Car drives fine and everything seems just perfect, EXCEPT, about 15% of the time when I push the gas hard from a standstill, there will be a slight resistance at about 5-10 mph, then the car just keeps going normally. When I say resistance, I mean, it seems as though something didn't catch right away...
I step on it from a stop, car begins to move, then at in the low RPM range of 1st gear, there is a slight... glitch, undetectable to anyone but me.
Also, I was at the grocery store the other day (Gelsons, none other! ;) ), and going slow in the parking lot, then stepped on it briefly, and there was a loud pop and I could hear and feel a clunk, this happened at about 5, 6, or 7 mph. I was going about 3 mph (still in first gr), I stepped on it, and the car made this loud POP and I could feel it and it held the car back for a brief second (less than 1/2 a second or something).
Again, this doesn't happen all of the time, just every one out of 5 or 10 times when I gun it from a stand still, there is jsut something not going/connecting smoothly. I would maybe think this was the transmission, but it doesn't feel as though the trans is slipping or anything. Though I have heard a similar (same?) sound from the trans before when coming to a stop (have also hear other stories from people about popping sounds from MB trans). But I don't think it's related to the trans, but it's possible I suppose. Also, about the same time I began to notice this, I had my differential fluid changed, and I cannot recall if it started JUST after I had it changed, or if it was after. Maybe this means something? I hope someone can shed some light. Thanks.

I know this is hard to explain, but maybe someone can help?

You didn't say what model your car is. If it's the C280 it's probably the electronic accelerator control.

It could also be the ignition coils breaking down. There are 3.

Hmm...
Interesting... never thought of these ideas.

If it's the electronic accelerator control... what does that mean? What is that? I don't have throttle by wire in my C280, that is, it uses a cable, it's mechanical.... Thanks.

for the "pop", suggest checking the health of your suspension components- closely../brake hardware/ exhaust system hangers/ trans mounts/ motor mounts>>something in these systems may be worn or loose

"lag" culprit may be related to the above or be: transmission/ driveline related, or suspension related = weight transfer causing the suspension to abnormally shift (worn bushings, etc.)

good luck & let us know what turns up.
-fad

If your car has the summer/winter mode switch for the transmission, make sure its on the s-position.

No S/W switch here...
but now that the idea of worn suspension components could play a role... I have a little more news.
My car seems less stable at high speeds than it used to. It seems more squirmy and more attention is needed to keep it in the lane. Also, upon flooring and then shift from 2-3, or from 3-4, the back end feels squirrelly (however that is spelled).
What could this be? Maybe they are all related? How and what suspension components should I check? Busings?! Excuse my ignorance, but I really don't know much about suspensions. Thanks!

Your engine in the C280 uses a variant of the 'fly by wire' setup. It does use a cable, but the throttle is all computer controlled.

That aside, I have heard these pop from time to time. Every one was a result of a lean pop. This is a term that is used widely in the industry.

You can have a lean pop from many different causes. One is if the adaptation is going out from an air leak or from the mass air meter being weak. The best way to check is have the fuel system checked for the adaptation. If it is above 1.1, the engine is running on the lean side.

One other thing to check is fuel pressure and delivery. I have replaced a hadfull of fuel pumps on C's.

Could be the fuel pump relay too coudln't it? I still have not changed that. And it acts up from time to time, usually when I'm driving about 15 mph, all fuel supply will cut out for a second, and then be fine, and then cut off for another second, then it just goes away...
And maybe the suspension is a different thing.
Thanks for the insight benzmac, but I have a question. If my car uses a cable, then the point of the fly by wire setup is only to detect throttle position (for whatever reasons, emission, computer, etc.)... correct? In no way can it over-ride the cable driven throttle, right? (My car has no ASR, or even ASD, if that matters).

It can override the cable because the throttle is driven by a motor. The only mechanical link is the LAST 1/4 of travel for limp mode.

It calculates what goes in and then uses a motor inside of the housing to apply throttle.

I know it sounds weird, but take my word for it.

I have only seen the overvoltage relay and the fuel pumps fail, not the fuel pump relays too much on the c280/

Thanks Benzmac! I had NO idea it was like this! I once attempted to change the spark plugs (attempt, was no successful), and i had the housing that goes from the air filter over the motor off and saw down the pipe, had someon push the gas and saw it move open. I guess I would think that my first idea is logical enough! Interesting... does the motor that opens the throttle ever break? That would be interesting...

(maybe this should be a new post...) What causes Limp home mode? And what is limp home mode? Only 2nd gear? What else?

Techs Help
 

Problem is still there, and progressing. But now I hear the pop more and more (along with the slight resistance), I'm beginning to think it is the suspension... and could it be the rear differential? I am definitly sure it's coming from under the car, and it's quite embarrasing because it's fairly loud sometimes!
Can anyone give me an idea?? Thanks a bunch.

I'm not sure if it applies but I"ve been told that when you change the differential oil on a jag (perish the thought) you have to use a special tool that deals with a spring load inside the case. If you don't, you get the same symptoms you are describing...one of the details the jag mechanics like because unless you're a jag tech you don't know this and the rear end very quickly deteriates to rebuild time. The technician who shared this with me said mercedes has a similar design on at least on some models. I don't know how accurate this information is ..just passing it along.

suspension diagnosis isn't easily described in a step by step receipe format.... since there are many parts that interplay (some with more critical roles than others in daily use)

their engineering, & performance interplay must be understood prior, the test drive characteristics/ observations/ conditions noted, specs reviewed, visuals on worn items noted, and.....I've seen on occasion a big lever bar used to test flex points and bushing conditions closer

its best to sit on the shoulder of a compent tech and have him/her explain their inspection process and reasoning for the resulting report card....suspension items do wear over time

-fad

Heavy Foot
 

Brother of The Benz, David
An article in the MBCA Star Magazine made note of combustion chamber pressure when the engine is driven with hard starts, full throttle exceleration.
The author made note of how the valves are slamed closed from the high combustion pressure resulting from full throttle application.
The price we pay for stoplight racing is short valve and valve guide life.
I know this doesn't help you resolve your problem, but the Star information opened my eyes and I'm looking forward to 200,000 miles before the cylinderhead has to be serviced.
Good Luck!
Happy Trails Beep Beep from The Spiderman in Houston!!!