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Hi Amazonphil,
1988 with the Bosch EZK117 (not turbo or is that the EZK115? Confoosed here) and LH-Jetronic 2.2.
Engine Performance Symptoms
https://www.brickboard.com/FAQ/700-900/EnginePerformanceSymptoms.htm
The causes for the subtle vibration are more than a few. Of click FAQ above Use the browser and search for the symptoms you describe.
OBD is sparse on this model (1988 and earlier models). What little there is is described here:
OBD 1988 & earlier to use limited LH-Jetronic and earlier OBD:
https://www.brickboard.com/FAQ/700-900/EngineOBDCodes.htm#Bosch22Codes
You can check the cap, rotor, sparks plugs (gap, make and model for proper temperature), and engine compression (faulty valve seat or compression bypassing the engine compression ring). Fail motor mounts, usually beginning with the air intake side (smaller) mount as the engine pulls up on the side. Unless your 1988 740 B230 engine leaks oil and soaks the exhaust side motor mount the engine and engine weight pushes down on the larger mount. If one mount is bad, best to replace them all including the transmission mount. In a perfect engine, replace with OEM mounts every ten years or so unless low mileage accumulation.
Search for vibration on this FAQ page:
Engine: Mechanical
https://www.brickboard.com/FAQ/700-900/EngineMechanical.htm
How old is the transmission fluid? The FAQ discusses two vibration causes.
AW70 auto transmission
https://www.brickboard.com/FAQ/700-900/TransmissionAuto.htm
How many miles? Consider the AW70 auto transmission output shaft bushing. You can replace the assembly with a new bushing. Consider the drive line as a vibration source.
A faulty or failing oxygen sensor leaves engine control to try to compensate without it. Yet other causes can lean or enrichen the engine and either way will damage the catalytic convertor. In all air filter boxes with the preheater flap valve, as your 1988 700 and my 1990+ 240s have, the flap valve ambient air thermostat fails to all heated air all the time and will end the life of an AMM/MAF in time. There is a CO adjustment on the LH-Jetronic 2.2 and earlier AMM/MAF. Yet you want to test for CO upstream of the cat.
Engine control sensor and testing:
https://www.brickboard.com/FAQ/700-900/EngineSensors.htm
Best method is to test the sensor at the sensor or through the wire harness at the LH-Jet computer (ECU) or ignition computer (ICU). Use some Deoxit-D or other low volt corrosion dielectric melting and inhibiting contact treatment. Use Deoxit-D spray sparingly on all engine control wire harness connector. The act of opening and closing the connectors breaks corrosion and treats the contacts on both sides of the connector including the injectors.
Read the FAQ for how to test engine control sensors using a digital electric multimeter. The FAQ indicates the values you should see. Also, search for articles in the RWD forum here for updated approaches and information.
I imagine the more than a single root cause. Before throwing parts at it, test, test, and test! Save your $$$$!
Also, review and research (test!) the causes your other post respondents provide you in this thread. My experience is limited to 1970s Bosch K-Jetronic and 1989+ LH-Jet 2.4/3.1 and EZK116 (crank position sensor era). Not well practiced with your engine control system version. Sorry.
Hope that hepkats (helps).
(Staying away from the) Eggnog!!! (Boyeeeeeeeeeeee!!!!)
Happy Eggnog Holidays!!!!!!
--
Beh.
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