M30 stumbling after vacation - any ideas?

[Adnan]

Hi,

I just got back from a 16 day vacation and fired up the 535 (5-speed manual) this morning. Though she started up fine, she would idle sort of rough (not real bad, just a feathery roughness over the usual M30 idle).

Every time I pressed the throttle in any gear, she would stumble and then seem to catch. The stumble isn't as if the engine wants to die, it's more like a hesitation. I was hoping that once warmed up it would correct itself but she continued this behavior all the way to work. It seemed that she was much better above 2500 RPM.

Any ideas? The car ran perfectly before the vacation. Plugs are fairly new but ignition wires are original (137k miles on the clock). Fuel filter? Throttle plate? AFM?

Thanks in advance,
Adnan

[DaCan23]

How far is your commute? After sitting for a while the M30 in my E24 has some moisture buildup that takes a bit to burn off.

[Adnan]

Hi,

My commute is about 15 miles/30 minutes. In the past, the car has never done this. We did have some heavy rains here in CA over my vacation so that may be an issue.

Thanks,
Adnan

[dave b]

Mine did the same thing after a long vacation...

It recovered fine after a little time and some "Italian Tune-ups"

I wouldn't sweat it too much

Dave

[Jeff N.]

Moisture in the ignition with all your rains. I'd get it nice and warm, may pull the distributor cap, and go from there.

Go anywhere on vacation you want to brag about? :)


Hi,

My commute is about 15 miles/30 minutes. In the past, the car has never done this. We did have some heavy rains here in CA over my vacation so that may be an issue.

Thanks,
Adnan

[Paul in NZ]

mine did the same after 10 days,Italian tune up fixed it.At one point it seemed like it was running on five cylinders missing and backfiring,that was on the way o work(40km each way) on the way home was fine...maybe take the long way home.Next time you go on vacation,take the car!

[Adnan]

Hi,

Thanks, that helps. I suspected condensation but not ever having it happen before with this engine made me worry that it may be more serious. I'll give it a few more miles and perhaps pull the dizzy and dry it out.

Vacation was primarily for my 25th college reunion so I flew in to Bombay and made a three day trip to the campus in north India (Indian Institute of Technology - Kanpur). What a blast! I had not been to the campus since graduating, nor had I met the gang in all these years. It was like stepping into a time machine - we were acting like kids again and making perfect fools of ourselves.

Back to reality now, though. I need another vacation to recover from this one.

Regards,
Adnan

[Incantation]

how empty was your gas tank? and do you live in a cold climate? could be something as simple as having condensation in your gas tank.. in the winter i always keep my tank at least 1/2 full and if i am gone for even just a few days i fill the tank up

[SRR2]

Most definitely could be the AFM. I posted about an experience with an M20 AFM (basically the same as in the M30) just a few weeks ago. You should be able to find this post. You can perform a quickie check on your AFM by measuring the resistance across the two terminals of the element on the AFM connector. Check the Bentley for which terminals to use. As you move the vane the resistance should vary smoothly from around 20-50 ohms up to a few K ohms. There may be a jump in resistance within the first few degrees of vane travel from a few tens of ohms up to about 200. This is normal. If you see large jumps in resistance (to over 1K) in the first 15-20 degrees of travel, your AFM is defective. You can probably extend its life by opening it and cleaning it. See my other post.

[Jeff N.]

...maybe car has a hangover too!


Hi,

Thanks, that helps. I suspected condensation but not ever having it happen before with this engine made me worry that it may be more serious. I'll give it a few more miles and perhaps pull the dizzy and dry it out.

Vacation was primarily for my 25th college reunion so I flew in to Bombay and made a three day trip to the campus in north India (Indian Institute of Technology - Kanpur). What a blast! I had not been to the campus since graduating, nor had I met the gang in all these years. It was like stepping into a time machine - we were acting like kids again and making perfect fools of ourselves.

Back to reality now, though. I need another vacation to recover from this one.

Regards,
Adnan