I recently purchased a 93 300e 3.2 (built in late 92) with 120K miles. There are few maintance issues that I need some input.

I read a lot of posting but still unsure and confused.

Belt tensioner - I replaced the belt. First I cannot find a 19MM bolt. Instead I have 10MM hex nut on the tensioner itself. It is not left hand thread. I losen it and the marker did not turn. Based on all the comments I read the tension needs replacement. Since I did not have a new tensioner, I just tighten the 13mm adjustment nut and tensioner nut. the belt feels tight.
Question - If I can tighten the belt as described, do I need a new tensioner? Why? Will the tensioner apply more presure to the belt after the adjustment is tighten?

Idle -
I think I have a vacuum leak. Please advise me of your thoughts.

Cold start - Start right away. Idle is smooth fluctuate between 1000rpm to 1500 rpm. Sometime idle smooth at around 1000rpm.

Warm engine - symptom is not uniform.
Sometime is very smooth (50 % of time).
Somethime is little rough (30%).....I see the oil presure gauge needle goes up and down. Car sometimes want to surge forward.
Sometime (30%) seems misfiring - idle at 600 rpm.
Acceleration and highway driving - smooth
I have installed new cooper core plugs. While doing it, I see small amount of oil inside the spark plug chamber. I have not replaced the connectors.

Your inputs are appreciated.

Earl

__________________
Earl
1993 300E 3.2
2002 C240
2007 BMW Z4 Coupe
1976 BMW 2002
1992 BMW 318i

The dreaded belt tensioner...leave it be. If your belt is tight, I wouldn't mess with the tensioner anymore...doesn't take much to screw it up and force replacement. A not so fun job. Save replacement for when your coolant pump goes south....it will have to get out of the way then.

Idle surge is a common problem as is indicative of a vacuum leak. I didn't bother to trace all of the ancient vacuum hoses, so I let my indie do it...problem solved.

Slight misfiring issues...plugs.

You have an easy car to fix, but don't throw parts or replace because you think it needs replacement...that gets expensive pretty quickly. When parts go bad on these cars, they'll let you know.

Sorry for the "short answer" versions, but I have to keep up with three of these models, and I don't venture into the engine compartments unless there is something amiss that requires my attention...

__________________
2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car

If knocking around under the hood...check out the wiring harness...the main harness that connects to your plug wires and such...common problem on these cars...and in my case it helped cause a misfire issue...if the insulation is crumbling badly...prepare to pony up some decent money for a replacement or plenty of free time to rewire it yourself...and yes your idle issue sounds like a vacuum leak...pretty common save time and let an indie do it...or get yourself a mityvac and have at it...that tool will come in handy in the long run...

best of luck

__________________
2004 Chrysler Crossfire

Replacing a vacum leak is the cheapest of several options when diagnosing a fluctuating idle, but it is not the only thing to look at:

Generally speaking, a fluctuating idle can be caused by the following:

1. vacum leak
2. bad mass air meter
3. bad throttle actuator

__________________
Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".

I might add that the crumbling insulation occurs on the individual wires inside the harness, not the main harness covering. From the outside, nothing will seem amiss, but if you cut away at the main cover, you will see the damage underneath.

I will also add that most W124s that were plagued with this ill have probably gotten this fixed early on...mine manifested itself as a problem around 90K.

__________________
2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car

Congrats on the car. I have the same car, also manufactured in November of 92.

I had the same issues with mine. My idle was eventually solved with the replacement of two coils. Soon thereafter I got the surging forward effect, which was fixed with a new MAS-not cheap, but an easy DIY.

Good luck

__________________
1993 300E
1999 E320 Estate