300e Idle Starting Diagnosis - PeachParts Mercedes-Benz Forum

Mcanix · #1 01-14-2003, 11:23 AM

I have a 90 300e with 160,000 miles. Symptoms are as follows:
On first and every start of the day, the engine fires for a second then dies.
On second attempt, it starts and stays running with a little nudge of the throttle. It idles rough at first then smooths out.
During the first 5 minutes of driving, the engine surges somewhat around 2200 RPM.
When warm it has a very rough idle.
I let the car sit for a week one time and it started great.
I got the car from my sister a few months ago and it has always had a bad idle.
I am out of town for two weeks and a mechanic diagnosed as follows:
When trying to adjust the mixture, he said his meter was jumping all over the place and would not stabilize which would necessitate replacement of the air flow meter at a cost of $1100.
My wife picked the car up and she said she barely made it home.
I am not second guessing him but I am not in a financial condition to cough up this kind of money. I have been an aircraft mechanic for 20 years and can remove and install just about any part but am not sure if I should tackle this myself due to the adjustments that would be required.
The plugs(copper), fuel filter, EHA valve, O2 sensor and EGR valve have been replaced. Some wiring for the O2 sensor has been replaced as well.
I will appreciate any replies.
Thanks,
John

G-Benz · #2 01-14-2003, 12:01 PM

I am currently dealing with solving some of the similar issues, and will shed a bit of light on what NOT to look for.

O2 sensor.

Air flow meter. I replaced mine with no change in symptoms, and btw, it's more like $250, not $1100!

Possible problems: Vacuum leak. Check all vacuum hoses. Intake manifold leak. Both can cause the surging problems you describe.

Coolant Temp sensor. Also can cause problems. About $30.

OVP. Source of all sorts of evil witchcraft, but related to hot start problems and rough idle. OEM part was deemed defective long ago, and replacement is improved. $65

I would find another mechanic though...$1100 to replace a $250 part that YOU can install in 5 minutes!!!???

So what is an OVP? DO a search and if you have a few days to peruse all of the threads, you will know more than you want to about this little relay.

Mcanix · #3 02-05-2003, 09:32 PM

Well, I was out of town and the drivability was so bad I had the shop replace the airflow meter. It ran great for 3 days and then became worse than ever and actually died at a stop light. I took it back once again and they said it was running super lean and adjusted same. I asked them about the OVP relay so they changed it as a precaution. I opened it up and it looked clean. Does anyone know of a way to bench check an airflow meter? I got the old part back and it didn't appear to have too much slop.
Thanks!!!

#4 02-06-2003, 08:01 AM

Too late....

One could have simply unplugged the old air flow sensor, drove it, and saw if the problem went away. The vehicle would have reverted to previous stored values in the ECM to enable to run properly.

sbourg · #5 02-06-2003, 09:58 AM

"The vehicle would have reverted to previous stored values in the ECM to enable to run properly."

I don't think so - I don't think there is any electronic open-loop control in the KE system. But, the effect is the same, since it is a fully operational mechanical injection system.

In this instance it sounds like the airflow meter was not the culprit, but something that attaches to it in the airflow path was temporarily sealing better, but has become loose again. The rubber in the idle control valve circuit (and everywhere else) hardens and becomes brittle with age. Leaks develop at connection points, or the rubber cracks. It is cheap to replace it all thru FastLane, but some of it may be hard to identify.

Steve

#6 02-06-2003, 11:49 AM

I appologize, I missread the model year, I thought it was OBD2.

Mcanix · #7 02-06-2003, 02:17 PM

When starting out this morning, the idle dropped to 500 RPM at the first stop sign. A mile later I stopped for coffee. It was trying to die.When I put it in Park, the idle was hunting between 500-1000 RPM. I shut it off and got my coffee. When I came out it wouldn't start. After a second attempt, it took quite a while and finally kicked with he pedal half way to the floor. I proceeded on havin to powerbrake it somewhat. At the first stoplight I was overwhelmed with the smell of raw fuel. I decided to limp home and take the wife's very reliable Suburban instead. I called the shop and asked that they pick it up as I have $1500 into a rough idle problem at the moment. Some may say, "why don't you search the Forum"? I just moved to the area for a new job, I don't have a garage and I have been out of town intermittently. I would like to find a way to verify that the air-flow meter is bad if possible. Can anyone reccomend a good MB mechanic in Peachtree City, GA? Thanks. John

haasman · #8 02-06-2003, 02:34 PM

I know there is not such thing as a cure-all and I don't want to seem like I am second-guessing anyone here, but I had similiar problems with the '91 300E, this is what I posted:

Irregular idle and sluggish warm starts

suginami · #9 02-06-2003, 04:36 PM

Sounds to me like a vacuum leak.

I had a similar problem, and after replacing the MAS air sensor and then the throttle actuator, the problem turned out to be a vacum leak at the intake manifold seal.

A vacum leak alllows "false air" into the system, and will prevent the MAS air sensor from doing its job.

pesuazo · #10 02-13-2003, 10:48 PM

Were you able to solve the problem?
I would like to know about it.

#11 02-14-2003, 04:40 AM

Having read a few of the responses here, have you thought about replacing the injectors, 160,000 mls is a lot for a set of injectors.

The injectors over time will clog up with gum, and will start to wear. The injector should be producing a fine cone shaped spray pattern. As you can imagine, if there is gum or wear, the shape of the spray is "corrupted", and may cause the injector to dribble.

When they dribble they are creating too much moisture in the cylinder and as a consequence it is a bit like flooding an engine, hence the engine will stop and will be difficult to start again until the gas has evaporated or you use the throttle a lot.

I needed to replace the injectors on my 190 2.6, and I was at my wits end trying to drive a "Benz" in such a way.

All the best

Bruce

DMarble · #12 02-14-2003, 04:26 PM

You don't look to be very far from MB Autowerks why don't you try limping it over there and let Donnie and his crew fix it right.
I would if he were closer than 1500 miles. PS They Sponsor this site.

Mcanix · #13 02-15-2003, 08:55 PM

The previous week, the shop towed it in and it ran perfect for them. The manager even drove it home and back (2 hrs.) and couldn't get it to screw up at all. PFM. The usual happened. Drove fine on Mon., Tues., and Wed. Thursday morning, same crap only I drove it all the way to work because I got tired of the car making me late. I drove the car for lunch and it did just fine. Wife had surgery yesterday so I didn't drive it. Tried to go to the pharmacy today and it wouldn't start after many revolutions of the starter.

When this all started months ago, I actually thought about changing the injectors but as I said earlier, my situation changed and I have nowhere to work on the car so I took it to the shop. I am actually over an hour away from MB Autowerks, but I've spent $1500 on the problem already with the current shop and I want them to make it right. I'll try again tomorrow and see if it will fire. Thanks to everyone.

#14 04-08-2003, 04:23 PM

I am new to this forum seeking the answers to same 300E problem as a lot of you are experiencing.
i.e Intermittent engine stall at low revs.

my local Mercedes specialist here in the UK has now had it 4 times and despite their best efforts, the fault always returns.

What I can rule out is :
Replacing all fuel injectors, done first
replacing the metering head.

I have called a halt to the repair process and am undertaking my own research on fine forums like this before I part with more hard cash.

I wonder if other peaople have become like me an expert at driving an automatic with 2 feet, braking with the left while maintaining 5-10K revs with the right.

I favour the ideas of the fuel injection treatment, then checking for air leaks in the manifold inlet. I will post any progress I make.

pesuazo · #15 04-08-2003, 09:32 PM

GarethBell, my solution to the low-hunting idle (500-1000 RPM), and intermittant stalling was solved by cleaning the Idle Control Valve (thouroughly, I also lubricated it with WD-40), as well as the throttle body-intake.