I had a pulsing idle which would bounce between 600 and 900 rpm. My first thought: vacuum leak. But it wasn't a vacuum leak!
I used a smoke machine to test for vacuum leaks. There were none. For good measure I retorqued the upper and lower intake manifold bolts, and the throttle body to intake manifold bolts.
PXL_20240911_160719162 by mike.bevels, on Flickr
PXL_20240911_162014581 by mike.bevels, on Flickr
I discovered it only happened when accessories like the fan or lights were turned on, so I looked at the alternator belt tension. This is when I disovered the lower alternator bolt was "free" and the nut was missing. I installed a new alternator in the beginning of 2023, so apparently I didn't tighten that bolt enough. Oops.
PXL_20240912_182605116 by mike.bevels, on Flickr
PXL_20240912_183748978 by mike.bevels, on Flickr
I fixed the alternator mounting and properly tensioned the belt.
I installed a new voltage regulator and alternator ground bolt.
PXL_20240914_170437440 by mike.bevels, on Flickr
PXL_20240914_171917019 by mike.bevels, on Flickr
I cleaned and swapped ICVs numerous times.
I swapped multiple DMEs, one of which has a bad coil driver.
PXL_20240913_181053706 by mike.bevels, on Flickr
PXL_20240913_181729362 by mike.bevels, on Flickr
PXL_20240913_180929257 by mike.bevels, on Flickr
I swapped multiple ignition coils.
PXL_20240913_200036767 by mike.bevels, on Flickr
I tested the AFM, TPS, and ICV with a multimeter. I readjusted the throttle body stop screw, which had worked itself loose last year.
And finally, I installed new spark plugs.
PXL_20240916_214545351 by mike.bevels, on Flickr
PXL_20240916_214935569 by mike.bevels, on Flickr
The voltage regulator and spark plugs had the biggest impact, really smoothing out idle in all situations. Catching the loose alternator mounting bolt was a blessing as that could have been catastrophic left unattended. Even with the stock DME, chip, and ignition coils, the car is running better than it has in a while.
Random E30 photo time!
20240913-DSC_1427 by mike.bevels, on Flickr
20240913-DSC_1442 by mike.bevels, on Flickr
20240913-DSC_1450 by mike.bevels, on Flickr
20240913-DSC_1448 by mike.bevels, on Flickr
20240721-DSC_8979-2 by mike.bevels, on Flickr
20240721-DSC_9025 by mike.bevels, on Flickr
I used a smoke machine to test for vacuum leaks. There were none. For good measure I retorqued the upper and lower intake manifold bolts, and the throttle body to intake manifold bolts.


I discovered it only happened when accessories like the fan or lights were turned on, so I looked at the alternator belt tension. This is when I disovered the lower alternator bolt was "free" and the nut was missing. I installed a new alternator in the beginning of 2023, so apparently I didn't tighten that bolt enough. Oops.


I fixed the alternator mounting and properly tensioned the belt.
I installed a new voltage regulator and alternator ground bolt.


I cleaned and swapped ICVs numerous times.
I swapped multiple DMEs, one of which has a bad coil driver.



I swapped multiple ignition coils.

I tested the AFM, TPS, and ICV with a multimeter. I readjusted the throttle body stop screw, which had worked itself loose last year.
And finally, I installed new spark plugs.


The voltage regulator and spark plugs had the biggest impact, really smoothing out idle in all situations. Catching the loose alternator mounting bolt was a blessing as that could have been catastrophic left unattended. Even with the stock DME, chip, and ignition coils, the car is running better than it has in a while.
Random E30 photo time!






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