1995 318i climate control lights flicker/engine RPM drops when idle

[88mm]

Hey all,

My 95' 318i has an issue where the defroster, air re-circulation, and A/C button will all light up for about two seconds, then turn off. The engines RPMs drop noticeably when this happens, occasionally bad enough it feels like the engine is going to die. I've observed this issue from outside of the car as well. When this happens the radiator fan kicks on for a couple seconds, then turns off. I cleaned out the fuse box with and checked all of the fuses under the hood. Everything seemed to look alright, not sure if i should do a continuity test on all of them or not as none of the filaments were damaged it seemed. The buttons don't work at all some days and other days when i press the buttons everything operates as it should.

It doesn't have an A/C belt installed at the moment. The battery is brand new, about a month old.

Has anyone else experienced an issue like this? What could I do to fix this?

I'm not sure where to start troubleshooting this issue. All feedback is greatly appreciated. Thank you very much.

[Thomas525]

When does this problem happen ?

[88mm]

I notice it when the car is idling in park. The buttons don't work half the time when i press them either. But sometimes they do work fine, or come on and off when I'm driving.

[Eric93se]

I would load test the car to be sure the alternator is good. You need a volt meter, turn on the car and then turn on all the accessories, head lights, AC blower motor on high, radio (doesn't have to be loud), rear defrost, high beams. With all that on, measure the voltage at the battery, should be at least 13.8V, if it's a lot lower then the alt is on its way out. Some alternators regulate at 14.4V others are set to 13.8V.

[Thomas525]

Ok. You have wires from the engine, and the cabin, which are rubbing each other with the insulation gone. Current bleeds into both at the same time sometimes and this causes the issue. This will take a long time to identify and fix. The shorter way is to do the driveability sensor disconnect test and see which specific engine sensor's circuit is causing this problem. You do that by disconnect the following sensors ONE BY ONE, testing your cabin controls in the middle to replicate the issue and if the issue does not happen when it should, then you have found the wiring from the sensor that is messing with you. Then you need to slowly trace and get to it. You will notice the problem area on the wiring when you find it. It will be visually obvious.

The sensors are: engine coolant temp sensor, air temp sensor, maf, o2 sensor, icv, vanos unit, I think that's about it. Some of these sensors will produce a slightly rough idle at idle once disconnected. No issue here, as we have other symptoms we can see if the problem is 'fixed'.