So I've been fiddling with this thing for months. Basically, the idle is rougher than i'd like it to be. Power seems low, and the transmission shifts as if it is not tuned to the engine it's attached to. This all happens when the engine goes into closed loop. On occasion It will start idling very poorly and hesitating/stalling off the line. Here is a list of things that I have done.

Spark plugs (h9dco)
injectors (genuine bosch) + seals
cap and rotor
Head gasket
rear muffler (rusted out, unrelated)
o2 sensor
adjusted duty cycle (tamper ball was missing)
air filter
cooling system flush
Fuel Filter

When it goes in to hesitation mode, The symptoms are exactly as If I held the EGR open. Vacuum decreases, Idle is bad, but at higher revs it is fine. I thought about checking the EGR for leaks, but I figured before I went and broke studs off, I'd ask first. The diapragm is fine and it snaps shut like its supposed to.

Fuel pressure is nice and high, around 80 PSI. Vaccum is around 15 when it is not in hesitation mode. I haven't gotten a good MPG reading since changing the injectors, but intown mileage is abysmal. around 210 miles per tank . Highway I got almost 27 mpg. I can't find any vaccum leaks anywhere. Anything else I do will be shotgun replacing, and I don't want to do that. What should I check out next? I really like this car.

edit: It starts as if there is air bubbles in the fuel lines or something. sometimes it start,die,starts. sometimes I just have to crank through some dead spots.

How old are the ignition wires and coil?

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Fred Hoelzle

Have you tried disconnecting the EGR valve, just as a test?

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The coil and ignition wires have not been replaced. I guess next on the list would be the wires. They look fine and test between 1.1K and 1.4K. I wouldn't know how to test the coil. Is it possible that the wires do need to be replaced?

Yes, I have the egr unplugged and so far it hasn't gone into really bad running mode, it does still run noticeably worse when It gets warm. Unplugging the O2 sensor to force it out of closed loop has no effect either. The serious hesitation seems very random, and just when I think I've fixed it it will happen again.

What's the compression on all 6 cylinders?

After a valve job, my 190E 2.6's compression is back to 185 psi on all 6. Prior to that, I had rough idling/misfire/intermittent stalling - #2 and #4 had low compression. New valves, guides and seals and she's been running great since last May 2012. We checked EVERY bit we could think of - CPS, trigger box/ignition control module, ignition coil, OVP, fuel pump relay, spark plugs, wires, distributor rotor/cap, etc...

AND... mine started okay when it had problems. When it warmed up, the symptoms would show.

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I've been messing around with my 1989 W124 300E for about 6 weeks now, very similar symptoms. Today, I finally fixed the last piece of the problem.

The car seemed like the engine was constantly battling the transmission. It would run fine when cold (running richer), then sometimes at temperature, it would run really rough, downshift and slam into gear.
At WOT, the car would move, begrudgingly. In town, at low throttle, you were very likely to get missing, skipping, arguing car.

Yesterday I went to a UPull-it yard, and happened to find a recently wrecked car that someone had clearly just put a bunch of money into. I scored an OVP, a reman-fuel pump relay, and a fuel distributor all for $65.

The OVP and relay are spares ($10 each!!!!!)

The fuel distributor is what fixed my problem. It was even effecting how the car shifted. Night and day difference.

If you, your multimeter and fuel pressure gauges have you this far, it might be worth the $60 rebuild kit online, or a trip to the wrecking yard.

I'm glad that you have fixed the problem. I've been suspecting the Fuel Distributer/EHA for a little while. I have no idea how it works or how to test it, but there is one on ebay for 87 bucks that came off of a rear end collision. I'm thinking about just grabbing it.

I could be wrong, and probably should do a compression test, but the car has relatively low miles and the head looked pretty good when I had it off. Anything is possible though. Thanks everyone for your suggestions.

It does sound like an EHA. Fuel dist is probably OK. They usually fail 1 of 2 ways... a leak at the plunger or failure to deliver fuel to 1 or more cyls.

Best test is to bolt on another EHA, preferably 1 that you know is good. Barring that bolting on any random EHA will likely shed some light on the problem.

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90 300TE 4-M
Turbo 103, T3/T04E 50 trim
T04B cover .60 AR
Stage 3 turbine .63 AR
A2W I/C, 40 LB/HR
MS2E, 60-2 Direct Coil Control
3" Exh, AEM W/B O2
Underdrive Alt. and P/S Pulleys,
Vented Rear Discs, .034 Booster.
3.07 diffs 1st Gear Start

90 300CE 104.980
Milled & ported head, 10.3:1 compression
197° intake cam w/20° advancer
Tuned CIS ECU
4° ignition advance
PCS TCM2000, built 722.6
600W networked suction fan
Sportline sway bars
V8 rear subframe, Quaife ATB 3.06 diff

FPR could also be getting tired, I know you said you had a pressure gauge on it, but did you ever have a gauge on it when it started acting up? A test would be to drive it with the fuel pump output socket jumped.

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That is a good idea. I'll try that this weekend.

There are no visible leaks on the fuel diet, and as far as I can tell, all cylinders are getting fuel at least to some degree. I've checked the plugs a few times and theyve never shown any signs of a less than healthy cylinder.

I wish I had access to another m103 car. Swapping the EHA is such an easy thing to do.

So its been a while since I've had progress, but I changed the EHA. Now all of my duty cycle numbers make since. At idle it stays consistent (it fluctutated like its supposed to, but before it would go all over the place and I would have to readjust). The 2500 rpm duty cyle is also good. For some reason now it chokes and backfires and have very little low end power. Once its moving it goes and goes though. I feel like the EHA was definitely a huge problem, but replacing it with a used, but good (as far as I can tell) one has changed the symptoms. I'm confused.