My son was driving his 87 740 4 cyl non turbo standard shift,wagon and went into a puddle that resulted in 4" of water coming in the passenger seat area. ( some puddle) It is still running but very rough and getting about 10 miles to the gallon. He has dried the computer out and sprayed wd40 on all the sensors. Does anybody have any suggestions to get it running properly again.

If speed was high the force of the water was very! strong, could have torn cables like the one to the oxygen sensor. Check it and rund OBD diagnostics.

Checked the o2 sensor, and all of the other cables they were good.

I will say that it was a big what I call a “puddle.” The road was flooded from a lake the ocean and lots of rain. The car did stall out ¾ of the way into it, and finally died just out of it. Four inches of water did come into the passenger side seat and to the rear of it. Located in the passage side is the computer for the fuel injection system which did get wet.

As for the engine compartment I could hear electrical shorts around the bottom of the intake manifold, but closer to the alternator. I pulled the cover for the fuse box and there was again shorting out noises.

All of the electrical connections were inspected and sprayed with an anti corrosion spray. The distributor cap was pulled and cleaned; no water or oil inside of it. The main fuel pump is working properly the in tank one has not been checked When the electrical plug is pulled off of the air mass sensor the car idles correctly. When it is plugged back in the car will again run super rich with fuel.

Any suggestions would be greatly appreciated. At the moment I am 90% sure that it is the computer, and 10 % it is the air mass sensor, even though it is unlikely that water was sucked into the engine. One of the sensor or computer either input or output is faulty.

Have you taken the distributor cap off and dried everything out in there? those things are notorious for letting water in ( same thing will happen if you wash the engine and dont cover the distributor good.
--
-------Robert, '93 940t, '90 240 wagon, '84 240 diesel (she's sick) , '80 245 diesel, '86 740 GLE turbo diesel, '82 Mercedes 300SD for sale