I believe I found the problem.

https://www.matthewsvolvosite.com/forums ... hp?t=17252

Under the paragraph describing some symptoms, item number one accurately describes my issue! Got myself a CRC kit to clean the ETM and MAF.

More to follow!

Well, with the cold weather no upon us, now I can smell the sweet odor of coolant when running the heater - However I can't not see any signs of leak near the heater core. Just cleaned the windshield looking for the obvious signs there....

Here we go again!

I have another issue with my same Volvo specimen, a ’99 S70 non-turbo, equipped w/a manual transmission.

Background : On 7/2013 I changed spark plugs at 100K miles, used Volvo OEM plugs from FCP Groton. Meticulously followed the process using dielectric grease.

The issue ...

Nope, no relation whatsoever. A bad heater core may also make a consistent, annoying film on the inside of the windshield that comes back soon after cleaning.

Go to the bottom of this thread:
https://www.matthewsvolvosite.com/forums/viewtopic.php?f=29&t=34056

I haven't tried it myself, but worth ...

One tip is the unexplained sticky stuff on some of the controls on my door, etc! Crap!
That's fairly normal for these cars; it's just a coating on the switches that wears off.

Do you smell coolant when the heater's run? Is the carpet near the gas pedal wet?

Thanks. So the sitcky stuff on ...

I found some videos on YT, I believe I have a heater core leak! One tip is the unexplained sticky stuff on some of the controls on my door, etc! Crap!

By the way, any pics to help in identifying potential leaks on the heater core?

Will do! Thanks for all the pointers!

Thanks! got some OEM stuff on the way.

I understand this is a close system, how much loss is expected over time if there are no leaks on the system? gee this car is 15 years old and I cant remember adding coolant since I bought in 99

Thanks! I'm the original owner and never seen any indications of leaks, but I will check it out. BTW, I have never flushed the system either. Thx!