I discussed with Patrick about his E32 750iL from 1988 without IHKA filter how to improve / avoid the smell engine bay in the cabin, here copied:
Want to add active charcoal air filter 88 750iL
I am thinking of adding an air filter somewhere in the intake passage. One possibility is to cut to size a layer of this 14 in x 17 in filter that is made for some other HEPA products. I have some rigid plastic grid that can be used to support flexible layers. https://www.amazon.com/dp/B075CB5VF5?psc=1 Are there some locations that I can fit one? Patrick C 88 750 172K
I assume it is for filtering the cabin air, as your 88 E32 does not have a filter for the heating/cooling, same like my 11/88 one. Rough idea: most of the air is sucked thru the 05 GRILLE,AIR INLET LEFT 51711928935 05 GRILLE,AIR INLET RIGHT 51711928936 http://www.realoem.com/bmw/enUS/show...diagId=51_0725 There you could install a filter sheet under these screens, that should be possible. But there are also smaller holes inside engine bay which let a bit of air into the space of the 2 intakes of the IHKA, for example behind the fuse box where the wiper motor is. So you would have to add addition filter sheets in front of the flaps of the IHKA for fresh air inlet, see pic here where the outside air temp sensor is shown, that shows the flap on pass side. shogun http://bmwe32.masscom.net/johan/ihka/ihka.html
Yes, for the cabin air. Because some engine oil smell always make it into the cabin starting some five minutes after car has warmed up. I changed the long weather seal underneath the hood and has helped somewhat but I haven't had that odor issues in other old cars that leak a little bit of oil. Thanks for the reply and info links. I guess while it's not rainy I can mount charcoal filter beneath the intake grill. A more permanent location is on both sides of the blower, although that means having to remove the bulkhead panel and expansion tank, and the blower itself.
permanent filter location on both sides of the blower. If you find a good solution, let us know with pics and DIY instructions, then I copy that and do the same on my car. I do not have any engine oil smell coming into the cabin now. Had it before, that was a leaking valve cover gasket on driver side, just at the firewall. Fixed that some months ago, re-sealed the intakes with liquid seal, added new breather valves, new fuel hoses and since then no more odor from engine. But I have to clean the heater core + evaporator every year with evaporator and heater foam cleaner, because of the dust coming in with the unfiltered air from the blower motor. I spray it into the intake flaps of the blower motor and also remove the side panels left and right of the center console, remove the IHKA temperature sensors on each side of the IHKA unit and blow thru these holes with ac/heater running the foam, the foam cleans the fins of evap and heater core and the dirty foam and fluid drain thru the drain holes of the IHKA to the ground, something like this http://www.lubegard.com/~/C-204/Kool...r+Foam+Cleaner
a good seal for e-box and fuse box between hood and the hood seal you need, then there is basically no air from engine bay coming into the IHKA flap area anymore, then only filters under the plastic grills below the windshield might be sufficient, see here the seals on a sample pic of the engine bay of the V16 https://img.gawkerassets.com/img/18y...g/original.jpg from this site https://www.revscene.net/forums/6878...mw-almost.html there are on each side at the fenders each one drain hole for rain water which comes thru the grills into the blower motor area, but these can be neglected.

And here the pics from Patrick from today and his comment: new e-box / fuse box seals and vent duct cleaning
Thank you Shogun for pointing out about the seals for both the e-box and fuse box. I installed new DIY seals above the e-box and the fuse box, and did a thorough cleaning of the vent ducts. Today I test drove the 750 around and didn't smell the oil odor anymore.
There is indeed a cavity below the right hand side air inlet grill that can be used to fit a charcoal air filter housing. I could look through the opening and see some of the cage fan blades deep inside; however, I didn't investigate exactly how a filter box can be hooked up to the blower motor inlet. I believe these days one can use a 3-D printer to fabricate such an adapter. I'd like to try my hands on a 3-D printer some day but for now I'll skip the idea of adding an air filter.

Here's what I did on my car: I used some toothpaste on the hood lining to determine that the rubber seals below never touched the lining. The factory spongy foam and sealing surfaces on the lining had disintegrated, and I'd never thought they were there for a purpose. So for a long time odor and fumes were able to easily enter the e-box/fuse box areas. Then when I removed the left and right air inlet grills I realized that there is no barrier between the e-box / fuse box and the space under the grills. Any fumes around the e-box / fuse box can immediately be sucked into the cabin. That's why in the past I was never able to fix this odor problem.
I took the opportunity to vacuum away the 30-year dirt and wipe down the cavity underneath the grills, and to empty out half a spray bottle of VENT AND DUCT CLEANER into the air inlet port by feeding the foamy chemicals through a long hose while the A/C was ON and fan was switched to HIGH. As for the disintegrated seals, I made new seals from some closed cell foam insulation sheets that used to be an old camping mat. Large area transfer adhesive was applied on the back to attach the seals to the hood lining. The rubber seals below now press deep into this foam seal as shown in the photo. Finally the 750 is all fit to drive.