Howdy all!

Was looking for a good commuter and a local gent had a 87 190D 2.5TD for sale - as luck would have it, we got on like a house on fire and I ended up taking the beauty home.

I'm fairly handy but have more experience with VW diesels than the Mercedes at present...

The car came with a huge stack of receipts (all the way back to 1990 or thereabouts) and has been well cared for as far as I can tell. It does however, exhibit an annoying behavior that I would relish the opportunity to vanquish.
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A previous owner (but not the fellow I bought her from) installed a boost gauge, which may provide a clue (possibly trying to track down this behavior)? Basically the turbo is behaving like an on / off switch at the moment, with a very fine threshold based on throttle input. On partial throttle (35-50% maybe) it will make about 5-7psi, anymore than that and it will immediately go to 13-15psi. Once you're in to the boost it will stay there until you cross back over the threshold whereupon it immediately drops back down to 5-7psi. Unfortunately this magical threshold occurs right where your foot is to cruise at 65mph or so- treating all onlookers to taking off like a rocket ship, only to slow down, and so on...

I'm planning on looking for vacuum leaks and hoping that will clear some things up. I've also read that I should clean the switchover valve and pressure sensor? Anything else that would be of use?

Otherwise the car drives pretty well. The glow plug light acts a bit weird where it doesn't always turn on when you turn the key on, but turns on after the engine is started and then goes out a minute or so later... I'm going to check resistance on glow plugs etc and see where that gets me.

Many thanks!
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First of all, your glow plugs are starting to go. The light behaves like that when one glow plug is bad, but don't bother trying to find the bad one. On this engine the only practical way to replace the plugs is to remove the intake manifold (no matter what you may be told). So you're going to replace all five and be done with it.

The waste gate on this car is pressure operated, very simple. But it may be binding, so get under there and squirt some penetrating oil on the pivot area. Replace the actuator hose. Other than that, a binding turbo bearing, but that's a long shot.

The behavior may be normal...the EGR valve is open in steady cruise, but will shut as soon as you drop the throttle. It may be that you are bleeding boost into the crankcase. You can test this by simply detaching the vacuum hose from the EGR valve. If you boost problem cleans up, then it may be a bad, EGR valve, vacuum proportioning valve or the EGR computer at the root of this problem.

sounds like a bad hose going to the wastegate


when you have a bad hose then the wastegate doesn't get pressure and the boost goes up to the point where the overboost valve limits fuel and the pressure drops where the fuel comes back on and the cycle repeats itself.