S70 RPM dipping too low when stopping.

Post by **kelvin6** » 04 Apr 2009, 22:05

Well today I did manage to change out the IAC valve with another one that I picked up from the junkyard (which I had cleaned out thoroughly) and so far I haven't been able to replicate the problem. Only time will tell.

It turns out the old IAC valve was covered (internally) in carbon deposits and blow-by oil. Electrically it does check out, but I suspect the amount of gunk I found in the valve could've been making it slow to react or plain gunking it up.

I will continue to drive and see if this problem comes back. Hopefully not.

Post by **kelvin6** » 08 Apr 2009, 18:21

Well the IAC wasn't the solution in the end.

I drove a good 80 miles today and at the beginning and at the end of the trip (when back on the streets) the dipping while stalling came back. I noticed when I was nearly home the car would dip in idle as well as occassionally have the feel of the car not being in the right gear (engine vibrating and lack of power) for a short period of time.

I did pick up a MAF from the junkyard (and cleaned it inside out) and I will give that a try.

I don't want to point fingers at the transmission... I really don't have the money right now to do any kind of replacement or work on it.

_HighVoltage_ · Post by **_HighVoltage_** » 08 Apr 2009, 18:50

I admit it might be a stupid suggestion, but what octane fuel are you using?
Also, how is your air filter.

The exact same thing happened to my car when I first bought it (20 minutes after I had left the dealership - nice huh?). I stopped to pay a toll at one of the bridges in NYC and the idle started to drop. Pulled the lever in Park and it stabilized. Pulled into Drive - started to drop again. It did it 5 minutes later again.
I didn't touch anything and for the past 2 weeks and 800 miles that I've put on the car, it hasn't done it again.

But if yours is doing it all the time, it might be more serious.
Try pulling it into park when you stop and it starts to dip - see what happens.

Post by **kelvin6** » 08 Apr 2009, 21:01

I'm using 91 octane and my air filter is new (less than 500 miles on it).

The odd thing I noticed today was that when it started again (it would do it for a short while), so as I was was slowing down I put it into neutral and the idle went to normal, but as soon as I put it back into drive and the RPMs shot up and back down (the car jerked slightly) and the UP arrow came on. All of this occured within two seconds and this was the first time i've encountered this. Bizzare.

Post by **E Showell** » 23 Jul 2014, 08:54

This is a little out there, and it falls in the correlation, but perhaps not causation category, but I have been living with a similar idle dip for a few years now and nothing seems to make it disappear -- until now. This past weekend, I replaced the electrical portion of my ignition switch and since replacing it, I have not noticed the idle dip occurring. Like I said, it may be correlation and not causation, but right now I think the two might be related.

The reason for replacing the electrical portion of the ignition switch was a strobe effect on the gauge lights on the dash. That seems to be gone as well. I did notice a fair bit of darkish brown oxidation on one of the contacts on the switch, but on only one contact. The other contacts seemed fine.

Reinie · Post by **Reinie** » 23 Jul 2014, 09:17

My 1999 S70 has this idle drop followed with a hesitation hicuup on acceleration. Usually when cold engine is starting to warm up. And mostly when proceeding through a stop sign. Doesn't occur real often, but its annoying. Recently replaced the entire pcv system with ipd kit to get rid of positive crank case pressure... Didn't fix the idle drop.

Post by **E Showell** » 05 Jan 2015, 11:50

I just changed the plugs on my car after 40K miles and noticed immediate eradication of the idle dip, but it's only been a couple weeks. I'll keep you posted. If you have a lot of miles on the plugs, you might consider renewing them. I use Volvo three prong plugs exclusively.

Post by **Brucebo** » 01 Apr 2015, 12:31

Was there any final resolution to this issue? My 2000 S70 has the exact same problem. It's definitely a transient issue, not steady state.

When coming to a stop, idle dips to below 500 rpm, then recovers (except when it occasionally conks.) Feels like the transmission is dragging the engine down until it "disengages" and the idle recovers. I can "compensate" by lightly pushing the gas pedal while braking.

I don't think it's the transmission though because if I put the car in neutral, race the engine, then suddenly let go of the accelerator, the rpms will drop all the way down below 500 rpms, and more often then not, the engine will conk. If it doesn't conk it immediately recovers and idles fine. Similarly if I'm coasting, with foot off of the accelerator, and put the transmission in neutral, the rpms will drop and more often then not the engine will conk. If it doesn't conk it recovers.

jabronijames · Post by **jabronijames** » 01 Apr 2015, 12:48

I had this problem for a while and then it got worse. My speedometer stopped working and the brake light and the ABS light would come on. Turns out a quick change of the Antilock Brake Control module fixed the problem. There's a guy who rebuilds them and did mine for me. Very easy to remove and very easy to re-install. He even has a video for it...
This is his website: https://www.midwest-abs.com/

Post by **Brucebo** » 08 May 2015, 17:43

In my case I swapped the ETM and that eliminated the problem. Feh!! I was reluctant because the symptoms were different than the ETM symptoms I had experienced before.

S70 RPM dipping too low when stopping.

Re: S70 RPM dipping too low when stopping.