1998 S70 2.4L N/A (non-return fuel system)
Recently my car started doing this. My RPM's will suddenly drop by about 500 or more for a period of a couple seconds, then shoot right back up to normal.

It seems to happen only on the freeway at speeds of 50+.
The engine sounds normal when it happens. It feels like it goes into neutral for a couple seconds, but there is no surge when they shoot back up so I assume the transmission is still in gear.

It happens both in and out of cruise control. I thought it was fuel related, but after replacing my Fuel Pressure Regulator, the problem remains. Does this sound like a transmission problem or electronic related? Or maybe my fuel pump is going out? I don't know. Rescue me please.

 

It could be your ETM (Electronic Throttle Module). There was a recall issued for 10 years/200,000 miles, a few years back. If you haven't had the software updated, and you're within the warranty, I'd go get that software update first thing.

I clean my ETM every time I change my oil. It gets gunky easily and causes jumpy acceleration. It could possibly be the cause of your problem. You need a 10mm socket ratchet, take out 4 screws, and then just clean it with Throttle Body cleaner and a tooth brush. The gunk comes away easily, and it's a quick fix.

The only other somewhat related issue could be your fuel pump relay... but I highly doubt that's your problem.

 

No warranty.

 

Crap ! How much does it cost for the fix?

 

What I meant by that was the 10yr/200,000mi warranty. You're over that, too?

 

Since his car is past 10 years, Some snobby stealers might not honour it.
I would try taking to a place that you have been to before, and had some Work done.

 

Well when my car was backed into I had the dealer do about 4 grand worth of repairs, maybe that's worth something.
Any other ideas? I kind of doubt it's a software problem as I've had my car for about 3 years and it's never done this until now.

 

My car does not have an electronic throttle module.

 

I suggest taking it to a Volvo specialist. I guess it's a good thing you don't have a ETM. Did ETM start In the 1999 models?

 

I would if I could afford it. I admit the Volvo is a bit out of my pay grade, but I love it and I am forced to do most of the work myself. A $700 repair bill would crush me.

I assume so because I think the biggest changes took place 98-99.
Mine is cable controlled.

A new clue: So far as I've been paying attention, the problem only comes up with the air conditioning turned on.

 

yes 99+ are the bad years for the etm

 

I recently got a P0505 code on my S70 that came back as an IAC (idle air control) valve fault. You might not have seen this code, but I wouldn't be surprised if this valve needed cleaning on your car. You can clean it just like the throttle body, with carb cleaner. It might be gunked up, causing your engine to have a hard time holding specific rpm.

Just a thought. The cleaning procedure is pretty simple, once you locate the IAC.

 

Well I recently cleaned out my IAC because the car is idling higher than normal, but it didn't solve either problem.
I noticed the problem happens with and without the A/C on.
It doesn't feel like the tranny drops into neutral, but there is a momentary power loss that I can feel and will alert me that it is happening.
It always picks right back up after giving it more gas.
Someone mentioned this might be the torque converter dis and re-engaging
and that it's normal, but Iv'e only noticed it in the last couple months.
If there is anything I can check or test myself please let me know.
Thank you

 

well... it's not a trans problem. The drop in RPM+ feeling like it's in neutral is your engine momentarily losing power. It's going to be either ignition or fuel related, but if it's only happening at freeway speeds, this might be something that will have to get worse before you can make it better.