95 850 T-5R Engine Twitching Randomly. Out of Ideas.

[E Showell]

I've had that same twitch in a '98 V70 for years now. If you figure it out, please let me know. Thus far, I've just lived with it. I haven't tried swapping out the IAC valve.

[T-5RShultz]

So I picked up another IAC valve from the junkyard and swapped it in, no change in the vehicle's behavior. Drat.

Well, at least that's one more thing off the "potential cause" list haha.

However, I did notice that inside the hose between the IAC and vacuum tree, there was a small, sticky snail trail of oil... Not pooling or wet, just a sticky oil residue in the hose. This same residue can be found at and around the charge pipe coupling at the top of the turbocharger, as well as trailing down the outside the charge pipe leading to the lower Intercooler inlet (I'm using stock intercooler pipe routing). I think I may have some turbo blow-by. Or is this normal? If not, I'm seeing a turbo rebuild/upgrade in my future...

Back to the "twitch" hunt. At this point I think I'm likely going to have to revisit the motor mounts and at least inspect them, despite all of them being replaced within the last 10k miles. The steering wheel shakes a LOT when starting or stopping the engine.

I will also look into any potential electrical/grounding issues. I have noticed the cabin lights (above rear-view mirror) tend to flicker ever so slightly while idling, and at similar intervals as the "twitch

I also wanted to add that my auto trans is on its way out. Something in the valve body is causing it to shift really harsh, especially at WOT and when going from D to R and back; it feels like I've been in several minor collisions every time I parallel park haha. I've had it "flushed" by a Volvo Master Tech using Volvo dealer equipment, and it helped a bit, but the main symptoms remain. Also, when "idle rolling", I can very clearly hear the gear(s) making a rhythmic whine with each rotation. The rhythm increases and decreases with RPM until I'm in 2nd gear.

I'm thinking that the transmission is possibly contributing to the "idle roll RPM dip" issue I described in my initial post. My theory is that since the TCU has to adapt/adjust to the tranny's failing physical components, it then in turn sends those wacky signals to the ECU, which also has to adapt/adjust, making the engine act funny. Just a theory, but does it sound plausible to you guys?

Thanks again everyone for all your help!

[E Showell]

My idle twitch is on a car with a manual transmission.