I would also do the O2 sensor for peace of mind and just go over the vacuum tubing to make sure they are not cracked or brittle and replace as needed. I actually replaced all the plastic vacuum tubing and rubber connectors under the hood. Its a fairly simple and inexpensive task. You can purchase several feet of plastic tubing and several feet of rubber connectors at Napa for cheap. I would also order the check air valves for the EGR and the air diviter (if it has one). Everything else is just you normal transmission flush, power steering, coolant, and make sure the S belt is in good shape and not cracked or wearing. I have the m103, but I suspect that the m102 should pretty much have some of the same components.

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1990 190E 3.0L

What is the air diverter? This car is a euro so no EGR or smog pump.

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68 280SL - 70 280SL - 70 300SEL 3.5 - 72 350SL - 72 280SEL 4.5 - 72 220 - 72 220D - 73 450SL - 84 230GE - 87 200TD - 90 190E 2.0 - 03 G500

Nissan GTR - Nissan Skyline GTS25T - Toyota GTFour - Rover Mini - Toyota Land Cruiser HJ60 - Cadillac Eldorado - BMW E30 - BMW 135i

89 would be too early for the emission stuff.

Plugs ,fuel filter, clean air filter, will make a big difference.

My car (m103) had a similar issue for a long time. My injectors where partially clogged.

Try a bottle of redline fuel additive before you start spending some serious coin on things that dont need replacing. If that does not help, injectors will be in order.

Vacuum should read at least 12hg. give or take. (not 100% sure) If you have an economy gauge, it should be almost pegged to the left running at idle, and 3/4-2/3rd, when at idle in drive.

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Eugene

10 E63 AMG
93 300te 4matic
07 BMW X3
14 Ford F-150 Fx2