Hesitation in '95 W124

[benzfanatik]

Hey all,

My 1995 W124 E320 has recently been giving me problems with hesitation and studdering. Sometimes, when I am at a stoplight, the car will bog down (500 RPM) for a split second and come right back up. Also, when I am accelerating, when the tach hits about 2200 RPM, it starts to hesitatae and will not go any higher, even with the pedal to the floor. If I let off a bit and give it more gas, it does fine. As soon as it gets to about 2500 RPM, it takes off like a champ. Also, I was tinkering around trying to figure out what the problem was and I noticed that if I rev the engine either in park or neutral, it acts as if it has a rev limiter at around 4500 RPM. It will get up to 4500, and bounce around between the 4500 and 4700. If I am driving and hit the gas, it goes past 4500 RPM no problem. The check engine light was on and I took it in, and the mechanic cleaned the EGR valve, which shut the light off but didn't fix the problem. Any suggestions or comments would be great! Thanks in advance

 

[jberks]

Hi,
The rev limiter does cut in at 4500rpm in neutral.

 

[OAPJinx]

Had a similar problem with my C180 and the ignition leads needed replacing as the hard plastic around the leads were cracked causing it to arc and hence misfire. May be worth checking

 

[mjtray]

There are a couple of well known issues with the M104 engine fitted to your car that can make them run badly and they are as follows;

1) Over Voltage Protection relay (OVP). If you have never replaced this relay, all of the original fail at some stage and cause all sorts of rough running. They cost about £45 and sit up behind the battery, behind the plastic cover the protects the ECU.....its just to the right of the ECU about 3 inches high, silver,with a fuse on the top. Takes about 5 minutes to replace once you have removed the battery.

2) Stumbling/surging revs. Typically shows up whilst you are stationary at the lights waiting for them to change. The car can start surging against the brakes and the rev needle will start hunting up and down.

This is normally caused by a dirty butterfly flap in the throttle body which causes a small air leak and confuses the ECU.

Its easy to clean....here goes....take off the trunking that snakes over the top of the engine from the air-cleaner. Also disconnect it from the mouth of the throttle body as it plunges over the edge of the engine on the right hand side.

Now you will be able to see into the throttle body. Inside you will see a round disk about 5cm down into the throttle body.....this is the butterfly flap. Spray some carb cleaner down into the throttle body. Get a screwdriver with some rag tied tightly around it and then push down on the edge of the butterfly flap. As it flips up you will probably notice that the edge o the flap has a build up of black crud on it. Cean this off with the rag and do it on the other side of the flap by pushing down on the opposite side.....this black crud stop the flap from sealing correctly.

Once done put everything back together again.

Now look at the trunking on the top of the engine, at the top right hand bend there is a sensor which is a push fit. Release this and you will notice that there is a fine wire element at the end of the sensor. Its likely to have a film of oil on it. Spray some carb cleaner and gently wipe it off with a lint free cloth.....re-fit.

3) If this does not cure it you may have a problem with your engine wiring loom, which Mercedes decided to experiment with in the early 90's by making it out of a biodegradable insulation....problem is it bio degrades too quickly and your car is fitted with this type of loom. Typical problems are rough running and all sorts of wierd electrical problems.......normally shows up with a check engine light comming on!!!. If your loom is on its way out you need to get it addressed quickly as it could screw your ECU!!!!

Good luck

 

[benzfanatik]

Follow Up

Hey folks,

Thank you are all of the info, I will try it out. It sounds as if the "loom" situation could be a problem...Where is it located, I would like to check it out and make sure it is not decaying....Also, someone told me the cause of my original problem might be that the timing is off. Would that casue the problems I mentioned above? Thank you all again for your help! :mrgreen:

 

[guydewdney]

the 'loom' is all over your engine...its the wiring loom for the engine..

timing cant really be off - unless a sensor is giving wrong values - does the diagnostic computer say anything? (get a proper check done at a decent indy with a star diagnostic)

 

[mjtray]

To check the loom where it normally fails....look to the right of the engine as you stand in front of it....there is a long wiring loom that runs alongside the fuel injector rail....its looks as of its covered in black masking tape...carefully peel off some of the outer insulation....underneath you should find loads of individual wires which should still be coated in insulation. If you see crumbling insulation and bare copper wires, your loom is knackered!

Follow this link for further info on the wonders of the M104 wiring loom problems

http://www.mercedesshop.com/Wikka/M104WireHarness

Good luck.

 

[Richie]

I thought i'd give my half'pennies worth, i have the same hesitation problem, however, it is an intermitent problem, some days it's fine, some days it hesitates. When i start the car first thing in the morning, if it starts first time, i get no hesitation on that journey, if however it takes 10-15 seconds to start, the car will hesitate when pulling away from junctions etc. Could it be the coldstart/choke system? Dunno, any advice would be appreciated.

Regards

 

[Richie]

Hesitation - Update

I was at my local Merc dealer picking up my spheres, so i asked him about hesitation etc, he said it was probably the Distributor cap and rotor, Went back to the car park and checked, sure enough, the rotor was black and arced, Asked how much a new set was, £50, did not have it on me so took the rotor arm off and scrapped it along the road to clean it, refitted and has not missed a beat since.

One more for the note book.

 

[trophykev]

Lost power - thanks guys

Hi am I glad to read this forum.
I have exactly the same 'no power' fault on my wifes 2002 A140.
As its intermittent and the computer shows no fault code we have had all sorts of stories from the dealer (I have a full maintenance warranty)

Driver error, pressing the brake and throttle together. My wife has size 3 feet. I drove it in motorcycle boots and couldnt accidentally press both.

Its the flywheel trying to catch up, its a heavy piece of metal..... this is the baby benz we are talking about not a 4litre range rover..

Final insult was last week - its a sticking valve in the gearbox, you will have to use the Tiptronic to manually change gear. They all do that even the big ones.

I suggested the sticking valve as explained by MJTRAY as I have had the same faullt on other makes but the 'mechanic' said "mercedes cant do that"

Just drafted a complaint letter to Mercedes UK then read this forum......

 

[johnrr]

M104 occasional hesitation

Hi all, I have a similar problem with my '95 E320 except mine only plays up when cold! Every now and again during the first 3-4 miles after a cold start the engine will hesitate momentarily and the revs drop by around 500 rpm. It only lasts a second or so. At first I thought the auto-box was changing up but its definately the engine. Have checked the plugs and HT leads. The car has done about 240k! The fact that it only happens when the engine is cold suggests a temperature sensor fault to me. Starting is always instant, hot or cold and performance and fuel consumption consistant. I have noticed that the insulation on some of the individual wires in the main engine harness, where they emerge to go into various plugs and connectors, is getting a bit crumbly but I've never experienced the kind of cutting out problems some people have had. Any ideas? How much does a new wiring harness cost dare I ask?

 

[svetor]

I was at my local Merc dealer picking up my spheres, so i asked him about hesitation etc, he said it was probably the Distributor cap and rotor, Went back to the car park and checked, sure enough, the rotor was black and arced, Asked how much a new set was, £50, did not have it on me so took the rotor arm off and scrapped it along the road to clean it, refitted and has not missed a beat since.

One more for the note book.

Hi, I am having exactly the same problem as described above, i.e. occasional rev hunting (and also occasional high idle). I am checking a few things these days, and I would like to give this a try.

Can someone please tell me where the 'Distributor cap and rotor' can be found?

Thanks