Rough Idle 94 E320 need diagnosis - Page 2 - PeachParts Mercedes-Benz Forum

duc4208 · #16 09-27-2002, 02:34 PM

TomO:

Your problem is the same as mine. I already fixed the problem. After washing my car's engine, a week later the car started to have stumble idle and it was intermittent. The malfunction light never come on. Ater the problem started, I replaced spark plugs, fuel filter, clean fuel injectors. The problem was still there. When I replaced the spark plugs, I noticed that the spark plug in cylinder #6 was orange. Water got into the spark plug well when I washed the engine. Because I parked the car on the slope driveway, water was geting to the spark plug well #6. Since you did replace the ignition coil boot and spark plugs, I would check to make sure that the replaced spark plug is not a resistant ones. Measure the spark plug resistant, make sure they are not high resistant spark plug (use Bosch copper spark plug only). Next, I would measure the resistant of the spark plug wires to make sure that they are about 2 kohm as specified by MB and have no crack on the insulation. Then I would took the ignition coils out and measure the primary resistance and the secondary resistance of the coils. The primary side of the coil between the connector terminals (12 V input wire) . The secondary side is between the connector of the boots to the connector of the spark plug wire. The primary side should be about 0.7 ohm and the secondary side should be around 6.7 kohm. Measure the three coils to see if they are consistent. This will help you to identify if the coils or the spark plug wires cause problem. Good luck

TomO · #17 09-27-2002, 02:50 PM

Thanks, Suginami, Actually I figured you all figured we'd do the wiring harness last. I've dreaded that harness since before we bought the car last fall, and have read your many posts since then. Earlier this week I called MBUSA, and they said it's probably time to replace it. I then called the dealer we bought it from (600 miles away) and they didn't volunteer anything, but said if it isn't crumbling they wouldn't change it (words to that effect). I figured I would think up a proposal to get something out of the dealer, since I'll most likely be stuck with doing the labor. So far the insulation I can see looks ok--but it is rock hard. I could have damaged the wiring while changing the plugs.

TomO · #18 09-28-2002, 06:07 PM

Thanks, duc4208. I tested the plug wires and two of the three have bad connections at the resistor ends! (I obviously should have tested them right away). The coil on plug #2 is OK; I'll check the other coils next. Looks like I got off easy (for the time being).

TomO · #19 10-07-2002, 01:25 PM

Update: I replaced the plug wires and connectors (But I did not test the new parts or the other two old condensors). I drove it about 10 miles. The idle is still rough but different. Before the new wires it missed very regularly--at least once per cycle. Now it starts right up and seems to idle perfectly, but then stumbles about every second. When I put it in R or D it gets much worse, stumbling erratically. It had very poor acceleration up to 3500 rpms. It pulled fine going slowly up our steep driveway. The check engine light stayed off, but when I pulled the general codes I got Code 2 (Oxygen sensor?). There were no detailed codes for pins 8 and 14. I will order a new sensor.

By the way, MB shop records indicate Code 7-8 and a new Air intake sensor April 2001 at 89k--six months before we bought the car.

Thanks again for all the help!

TomO

suginami · #20 10-07-2002, 01:38 PM

Code #5 is for the O2 sensor.

I am 100% convinced that you need to replace your engine wiring harness.

You have all of the symptoms

Rough idleing, missing, stumbling, random and arbitrary fault codes.

It's your wiring harness. About $550 for the part and 2.5-3 hours labor.

Arthur Dalton · #21 10-07-2002, 02:25 PM

Code 2 os O2 sens.....

5 is egr

suginami · #22 10-07-2002, 03:09 PM

oooops. My mistake.

miktvk · #23 10-08-2002, 09:20 AM

gotta weigh in on this, I agree with with suginami, don't throw any more parts at this until you check the condition of the ignition wiring harness, I guarantee that you will find brittle, flaking insulation.

We briefly had a 94 E320 with this defect, and now I see that our 95 (with 108k) suffers from the same (although still running well).

No help from MBUSA on a mass defect afflicting '93-95 M104 and the V8's as well.

#24 10-08-2002, 12:16 PM

Tom,
I'm Certainly no expert but I have had a similar experience on my ’89 260E with 120K. I had to keep my foot on the gas a bit at a stoplight to keep from stalling although the car started right and ran the highways perfectly. Prior to taking it in to the shop I ran a can of Gumout injector cleaner and some gum must have gotten cleaned out because it perfect as a Mercedes should be. Needless to say, no shop time was required and I’m a happy camper..

TomO · #25 10-08-2002, 02:11 PM

Thanks to all for input.

This morning I drove 5 miles into town and it seemed to be running better and better. Idle and acceleration at low rpms are both better but not yet perfect. (Does the engine's computer "learn" as it goes?) I still plan to install the o2 sensor (120 k miles) and a new fuel filter (unknown age), and I think I should clean the egr valve (help--I still can't find it). I read some posts about the ovp relay but got confused--could the ovp be part of the problem too (I'll check its part # tonight)? Other than that, I will buy no more electronic parts.

As to the wiring harness: My plan has been to check and replace the obvious culprits (plugs and plug wires; O2 sensor; fuel filter) before I write the owner of the dealership I bought the car from and beg for a new harness (for free or at a very big discount). The problems are 1) both the service manager and the parts department there have told me they have never heard of this bad wiring harness problem; 2) the dealer is 700 miles away.
3) before I spend my own money on a new harness I need to r&r the serpentine belt and pulleys (cracks on ribs every 1/16 inch) and the driveline (play in ujoint). But that is another topic.

TomO · #26 10-09-2002, 11:38 AM

My OVP is part 000 540 67 45 and has a single 15A fuse on top; I gather it should be OK?

Yesterday morning's diagnosis was apparently due to a combination of cool temperatures, low expectations and wishful thinking. It ran poorly in the afternoon.

I erased the fault code #2 (held the switch for 6 seconds until the red light went out; waited 30 seconds and tested it again and still retrieved code #2 ).

suginami · #27 10-09-2002, 05:26 PM

Well, it could be your O2 sensor, but you've had lots of codes, and I think all of them are bogus.

I'd get a diagnosis on the harness before I'd replace anything else.

TomO · #28 10-09-2002, 08:07 PM

Suginami, That is just what I keep thinking! Ugh.

jsmith · #29 10-10-2002, 07:38 AM

i wonder what our average number of wire harness related posts is per month. must be at least one, i'm pretty sure i saw at least one other this past couple of weeks...

stevebfl · #30 10-10-2002, 08:22 AM

I have just read this post for the first time, probably quite unusual for me. I have been out of town attending some very interesting technical conferences.

I am intrigued at the level of diagnostics that have evolved on this problem and I wonder if all the audience thinks that techs use such technique.

I haven't heard one level of diagnostics used here except for fault codes. We have no comment to what actually is happening. Do we have single cylinder misfires? We have no information on secondary voltages and burn times. All available with a competent scanner and probably a key to the idle answer.

Is closed loop activity initiated soon after cold start? What are the adaptive values at idle, lower and upper partial load?

Parts swapping is definitely part of these diagnosis. But that should be the job of a technician not the customer. Air Mass Meters almost always have to be swapped to prove a defect. The adaptive values are watched before and after and the car is used for the test. Small dynamic defects are compensated for by the management software and even MB says that scan data can not predict AMM problems except through fault code (major problems - not performance problem) Change in adaptation values combined with a hypothesis that explains symptom activity, is the diagnostic concept.

My first guess would have been the coil connectors and the other ends might as well be shot gunned next. If that doesn't do the job, a proper analysis might be the next answer. Start with someone with a scanner that will give the secondary firing voltages and burn tiimes. It gives him a quick window.

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