Tech changed plugs -- now it runs rough. - PeachParts Mercedes-Benz Forum

brookspw · #1 08-06-2003, 09:57 AM

My car had a very short (1/4 second) stumble in the idle immediately at startup. Other than that the idle was very smooth.

He said I needed new plugs. Fine. He changed them.

NOW, it won't start unless I give it gas. If it does, it runs very rough and won't smooth out until I give it gas. Even then, it runs rough.

What could it be?

[He said that before long I'd need a new distributor cap, rotor, O2 sensor, and wires.] Maybe, but with the current ones it was running very smoothly, now it isn't.

Yes, I checked. All the wires are securely attached to the plugs.

This is a MB-only, certified tech.

Arthur Dalton · #2 08-06-2003, 10:06 AM

Use Plats???

jay3000 · #3 08-06-2003, 01:48 PM

Did it run that way IMMEDIATELY when you picked it up??? Or is this something that has developed lately??

yal · #4 08-06-2003, 01:59 PM

Quote:

Originally posted by Arthur Dalton
Use Plats???

Yep I bet you he used plats. Either that or he gapped them wrong.

Also check your wires, make sure they were put back securely.

haasman · #5 08-06-2003, 02:09 PM

... or ressistor plugs were installed .....

brookspw · #6 08-06-2003, 02:29 PM

No plats. Now, however, I see that they were H8DC. I looked them up and it says they are the "small style", and are listed for the following:

Spark Plug - H8DC (New Style - Small Size)
Parts # 002 159 58 03
Model: 190E 2.3-16 -- M102.983
Model: 190E 2.3 -- M102.961
Model: 190E 2.3 -- M102.985

Mine, obviously, is an M103, and it shows that I should have H9DC.

I don't know what would make 1 work and not the other. However, is this enough to cause my problems?

Also -- what are "resistors"?

It did this from day 1 after the repair.

haasman · #7 08-06-2003, 07:09 PM

Here is my guess: I don't think it is plug rleated UNLESS a plug wasn't check for a proper gap.

It could instead be related to a wire or connector.

I hate to admit this ...... OK here goes ..... I was going crazy trying to figure out why the 300E idled roughly every so often. When I recently changed the plugs, the loose spark plug connection on cylinder # was the obvious reason.

Check each connector. Twist them gently and tug on 'em to make sure they are on securely.

Haasman.

brookspw · #8 08-06-2003, 07:11 PM

I'm going in tomorrow to have him check it out. He said he also "leaned it out" and maybe he went to far. I am assuming he means fuel mixture -- by what method would he have done that?

haasman · #9 08-06-2003, 08:09 PM

Maybe just coincidental timing and the cap and rotor should be replaced now. Your tech said they were going to need to be replaced.

Haasman

brookspw · #10 08-06-2003, 08:28 PM

Yep, I'm actually going to do the cap, rotor, and wires.

How about this from 2phast's site:

Quote:

Although I don't have any pictures of this, the O2 sensor is a three wire Bosch unit that the dealer wants over $200 for. After some careful research, I found that the 1990 Ford Mustang 5.0 uses the exact Bosch 3 wire O2 sensor, but with a different plug on the end. I bought the Mustang O2 sensor for $36 and cut the plug off my old O2 sensor and spliced it onto the new O2 sensor. Works perfect!

What do you think / how would one verify this?

jay3000 · #11 08-07-2003, 08:10 AM

Quote:

Originally posted by brookspw
I'm going in tomorrow to have him check it out. He said he also "leaned it out" and maybe he went to far. I am assuming he means fuel mixture -- by what method would he have done that?

Ditto on that.. Mide did the same thing when I leaned it out too much... By adjusting the Lambda...

brookspw · #12 08-07-2003, 05:44 PM

Well, I seem to have a resolution.

He whips out a hex wrench, goes under the hood for about .19026 seconds (

) and says, try that. It seems smooth as silk again.

I typically get about 20.5 MPG. With the too-lean mixture I used a full tank and got about 18.5 (which seems backwards -- ? ).

I'll update after a tank.