E320 Mercedes-Benz idle problem, please help!


I have a 1994 Mercedes that runs just fine when the engine is cold, but when it reaches normal running temp. it surges (500-1000 rpm) when ever you come to a complete stop. If you try to accelerate slowly it misses and sputters for about 10 feet and then it picks up and runs just fine. If I keep my foot on the accelerator and maintain an idle of 1000 rpm when I stop it accelerates with no problems. The surge is also there when in park. The check engine light is on. Any suggestions or ideas for what this might be caused by would be appreciated.


You need to find out what is causing the “Check Engine” light to come on. One of our resident Benz experts will undoubtedly chime in with the procedure for pulling the error code(s). The usual advice to go to AutoZone etc. won’t help because your car is too old for their code scanners.


I agree, take it to a good benz shop and have them check the codes. My best guess is that you have some issue with the cold start system, or maybe just a vacuum leak.


i;d second the vacuum leak thought, but getting the trouble codes is the first stop on the road to recovery.


I have a local Mercedes dealship, would this be the best place to go, or do you have another suggestion?


Thanks for the help.


“I have a local Mercedes dealship, would this be the best place to go, or do you have another suggestion?”

Dealers are no better (or worse) than independent mechanics for almost anything you might need done on your car. They will almost always charge more per hour and often more for parts and supplies. They also tend to look at repairs a little different than the independent.

A dealer may well recommend work that strictly may not be needed, but could be connected to the problem or maybe replace a part when a little repair would fix it ALMOST as good a new.  

I suggest that most people would be better off finding a good independent (Not working for a chain) mechanic.


although you can take it to a dealership, ins’t there an independent mechanic nearby who specializes in mercedes? a dealership is going to soak you price wise.

ask some friends, co workers. relatives. know any other mercedes owners? ask them.

BUT, you really should get the check engine light diagnosed.

BTW, did the check engine light come on around the time the reving, sputtering started? in the future, when the check engine light comes on you should really get the engine checked out. sometimes early intervention can make what was essentially a 100 dollar filter, sensor repair into a delayed 1000 dollar multiple repair.


You don’t have to go to the dealer if you have a good independent benz shop; I would not take it to a general shop because they are unlikely to be familiar with the car and may not be inclined to “really” fix the issue. My independent is probably better than my local dealer (and probably more expensive too). You need to have someone you trust for future work anyway, dealer or independent.


How’s your German?


Check the codes, but it sounds like the MAS sensor. Known problem area. Don’t replace the whole unit, just the insert. Big cost difference. Many dealers and shops just drop in the whole unit…



Auto Zone auto parts has the MAS (Mass AirFlow Sensor) for $154. It’s a Cardone brand…a perfectly good brand, as far as I know. A shop wiil charge you $230 for the same part, plus labor. A dealer will only install the Bosch brand, and charge you $500 parts, plus labor.
This job is, “so simple, even a caveman can do it” (or, any novice mechanic). In fact, it would take great effort to mess it up.


You can get the entire correct (bosch) part for $275 retail (see benzman’s post for just replacing the insert):


Autozone is good for buying fluids and light bulbs, personally I wouldn’t buy any real parts there.


I just traded my Malibu to my daughter for the Mercedes. God only knows how long the light has been on.




I am convinced that you are correct and the MAS is the problem. I know my way around GM cars but not so with Mercedes. Where is the unit located and what does it look like? Thanks!


Here is a ton of good info on the MAF on 90’s Mercedes’




Hope you read the article shown to you by Benzman (GOOD job, Benzman). If you use a spray cleaner, like MAF Spray Cleaner, you may save yourself some “gold”. Use Carb/Throttle Body cleaner to clean the iac (idle air control) valve, and the throttle plate and bore.
I see you’re still asking, “Where is such and such?” This makes it clear that you still haven’t gotten the repair manual. If you couldn’t find the MAF, how will you ever find the iac and the throttle body? Save MORE gold, get the repair manual (and, of course, use it, to great advantage!)