S70 RPM dipping too low when stopping.

Post by **kelvin6** » 21 Mar 2009, 22:47

My Volvo S70 has been experiencing a problem for months where when I would be coming to a stop from a regular speed, about 50% of the time the RPMs would drop well below idle and nearly stall the engine out. This only occurs when the car has been driven warm/hot (like 45+ minutes of driving or agressive driving). It feels like the transmission is also holding in gear too long pulling the idle down, but I could be wrong. I guess its also possible that the IAC isn't getting the signal quick enough to activate to prevent the Idle drop.

I'm getting frustrated with this. I thought it was my transmission going whack, so I checked the level and found it was slightly above high and corrected that. I thought it was my MAF, a good cleaning didn't fix it. (sigh).

I guess its some sort of electrical problem and it feels like its related to some sort of "Heat Soak" because it only occurs when hot. Is my MAF dead (original all 203K miles)?

Someone please help. I checked for vacuum leaks and can't visually find one, which i'm currently battling a P0455 code (which started as a P0442 and grew to the P0455).

Post by **Ozark Lee** » 22 Mar 2009, 04:54

P0445 is the evap purge valve, P0442 is an evap leak. Neither should be causing the car to stumble when you stop. That sound more like the torque converter lock up not disengaging. Check you brake lights and make sure they are working.

...Lee

895meztz94 · Post by **895meztz94** » 22 Mar 2009, 13:47

First I'd say ETM issue, but you have a 1998.

Craigd2599 · Post by **Craigd2599** » 22 Mar 2009, 15:46

I'm with Lee...try your brake switch.

Post by **kelvin6** » 22 Mar 2009, 17:20

I guess it does feel like it the torque converter is not disengaging properly, but the brake light switch is linked to the car computer (which signals the TC)? Really... I never knew.

Craigd2599 · Post by **Craigd2599** » 22 Mar 2009, 17:58

well the ecu monitors the abs as well as the lockup which are both brake pedal triggered

Post by **kelvin6** » 22 Mar 2009, 21:08

Hmm, I haven't gotten any honks (from others) or any signs that my brake lights aren't working, but I will take the switch out and check. Strangely this problem seems to occur when the car is hot (most of the times) and very rarely when cold or barely warmed up(which I experienced today).

I wonder is there a write up on how to get it out or is it self explanitory?

I was worried that it could've been the MAF, IAC, Coolant temp sensor or even the TPS! I even went as far as to take apart the ECU to see if something obvious failed (like failed capacitors) and found nothing.

Post by **kelvin6** » 31 Mar 2009, 14:24

Well I did replace the brake light switch and the problem is still present.

I also noticed (and i'm unsure if its normal or not) that when my car is in position II on the transmission mode switch a LED lights up on the W button, goes away when car is started (I don't recall this light coming on before).

I've scanned the car with Vol-FCR and found no codes in the ECU and TCU.

I guess what's next is the IAC...

Any ideas anyone?

Post by **kelvin6** » 31 Mar 2009, 21:21

I've also noticed something another symptom. When the car starts to do the RPM dipping when stopping, the transmission also seems confused about what gear to be in. So usually if I don't make a complete stop and hit the gas the car jerks and lags for a bit. Sometimes even vibrates, feeling like the transmission is "buzzing" or kind of in between gears...

I'm just puzzled by this whole issue. I'm trying everything I can. I'm even more puzzled why the car only starts doing this when its hot... leaving me with all sorts of possibilities such as IAC or even the TCU going nuts.

Post by **mom** » 03 Apr 2009, 18:15

I had the same problem lately, I tried to clean the MAF like you did but idle was still dropping while stopping. I changed the MAF and no more problem. I had a check engine light coming on and off also (p1171).I had around 90 000 miles on it. A lot of people here had problems with their MAF, by chance it's not that expensive around 125$ at FCP.

The MAF has conductive wire inside, depending of the volume of air passing through it, the resistance of the wire is changing. So maybe the wire is becoming too hot or too cold after a couple of miles ?

It's my opinion but I could be wrong.
Good luck.