I have a 1989 240 DL (5-speed manual, M47) and today was raining and it was my first time using the wipers. When I was releasing the clutch to get rolling, the car stalled. But it wasn't a "driver-error" type of jerky/uncomfortable stall, it was sorta a quiet, gentle stall. It was a very smooth small/engine die.

So I did not know what to think. I couldn't remember myself letting the clutch go too early or too fast, because I'm pretty competent at manual now. Still a little rusty, but not bad enough to stall (although I won't jinx it).

A couple hours later, I was parked in neutral checking my phone (with the wipers on) and I noticed the RPM's dropping about 500RPM whenever the wipers would rotate, and they would go back up to 950RPM to 1000RPM when the wipers stopped rotating.

To replicate the problem, I held the clutch at the engagement point and let the wipers do their work. RPM's dropped super low due to clutch being at engagement point (so this engagement point causes the RPMs to drop) and the wipers took off another 500RPM, and the car almost stalled, so I push the clutch back in to prevent stalling and I am almost certain the alternator is the issue.

I've read that the 240 alternators are sort of weak and cannot handle many electronics, but this may be an untrue/unconfirmed rumor.

 

The alternator in your car should be sufficient to handle all the electronics that your car has. It was designed that way. It may be getting weak - after all, its a 24 year old car. You can test this though. Get a voltmeter and check the voltage at the battery. With the engine running (idle), the voltage at the battery should be between 13-14 volts. Turn on accessories (wipers, blower fan at full blast, etc), it shouldn't drop below 12.5 volts. If it does, you may have a weak alternator. However, prior to replacing, I would do the same voltage check from the post with the big red wire on the alternator. If it checks out there, you may have a bad ground and/or connection.

By the way, is the Batt light in the instrument cluster working when you turn the key to the II position? If not, your battery will not charge.

 

Alternators are not weak on these cars. Check the output, check the belt-make sure it's tight. Wipers should not make the RPMs drop by 500... This may coincidental...

 

wipers should NOT make the RPM's drop 500. idle is only 700-800, so dropping 500 woudl be a stumbling slow 200-300, engine won't idle smoothly there.

I'm gonna hazard a guess that there's a flakey ground on the wiper motor. or maybe the motor itself is really tired, and is drawing too much current. its a very easy wiper motor to replace, I supervised my 17 yr old daughter through a replacement, she was proud of herself!

 

Okay, the weather has been much better lately, and by that I mean warmer. And this issue went away. It starts with a low idle for a second or two when you start it, but goes back up to normal levels, such as approximately 750RPM. I don't know if this issue is weather-dependent, I'll have to see until the next rainy day to see. I tested the battery and it doesn't go much below 12.6 volts when I turned on headlamps (incl. high beams), air conditioning, defroster, radio, wipers, etc. I'm assuming the alternator is fine as well, due to this. I'm just going to wait and find out, I'll see what happens. I'll make sure to post here with more information, thanks for your guys' troubleshooting advice and help.