99' V70, Runs fine then rough idle and dies with gas press

nightc1 · Post by **nightc1** » 21 Jun 2010, 07:26

I am ordering a new o2 sensor but I can't seem to get the harness plug disconnected so I can 100% verify the ones listed have the correct harness connector. I've looked at the part at groton and still just can't figure it out. Getting one hand on it is pretty easy from the hood side... getting 2 is a pain but possible though I can't look at it in any way at that point. I put a good hour into messing with this on friday to no avail. I can remove the O2 sensor without issue. It was surprisingly easy. I was kind of shocked that both 02 sensors are so close together on this car. Anyway where the wiring routes up between the engine and firewall and below the brake fluid reservoir... I just can't seem to get a good enough look at it to figure it out.

If no one here has any tips, I may just follow the next harness around and under everything and see where it goes and try to disconnect further up. But that is going to be a headache since there's so much in the way.

I guess I could also just disconnect the 02 sensor from the exhaust system and gently pull it through the tight quarters with the little wire holders removed and see if it creates enough slack at the harness connector end that I could pull it up out of the engine compartment to get a good look... but I'm not sure I have enough space to get it through. It would be so much easier to just know how to disconnect it.

Tips?

Retired MVS Contributor · Post by **Retired MVS Contributor** » 21 Jun 2010, 07:37

A dumb question...Is ir possibel that you put diesel fuel into it?...

nightc1 · Post by **nightc1** » 21 Jun 2010, 07:40

No.

I fill up at the same place and diesel isn't an option on the pumps. I think the only diesel they even have is on a single pump off away from the rest of them.

Turns out it is the O2 sensor according to an OBD2 cable/software combo I picked up. So I need to replace it but first I need to figure out how to disconnect the silly harness connector between the engine and firewall (just below the brake fluid reservoir.

Lutley5060 · Post by **Lutley5060** » 21 Jun 2010, 15:45

It sounds like you could have a bad IACV or whatever Volvo calls it. If you can hold the brakes and push on the accelerator until it is at a higher-than-idle- RPM, and from there the car runs fairly smooth, you may have a bad IACV.

I had a similar issue with a different make and model. I found out that my teen age driver had driven the car through some large pools of water during a heavy rain storm. Apparently, the water entered the intake and contaminated/damaged the IACV. I replaced it, and it cleared up the problem.

nightc1 · Post by **nightc1** » 22 Jun 2010, 09:42

I looked it up and this car has an IACV and I found a thread elsewhere about how to clean it...
http://www.volvoforumsrepairs.org.uk/800Repairs/iac.htm

But I'm not getting a code for that being the issue. It seems to be the (edit: Front) O2 Sensor... but I am having issues figuring out how to disconnect the harness for it.

Still, I appreciate the feedback and this is something I can definitely check out. Maybe it's partially clogged or a hose is cracked there or something. Still, it seems the O2 sensor is the culprit for my main issues at the moment.

jgray850turbo · Post by **jgray850turbo** » 01 Jul 2010, 20:13

I just had to fix the O2 connector on my 95 850 turbo, I'm not sure if it's the same type of connector. On mine there is a orangish clip-type thing that keeps the plugs together. It slides only to one side, though not all the way off, and then you can seperate the plugs. Rinse and Repeat. Hope it helps.

Post by **pkc303** » 01 Jul 2010, 22:21

Check the vacuum hoses too.

Post by **SniperCat** » 02 Jul 2010, 09:14

Did you get it fixed? What's the fuel pressure reading? Also (this was me yesterday) check the hose from the innercooler to the throttle body pipe. Let us know.

nightc1 · Post by **nightc1** » 01 Sep 2010, 21:52

Well, TODAY I finally figured it out. After disconnecting the cat, replacing plugs, replacing a fuel filter, replacing the fuel cap, cleaning the MAF, (and all the hoses in that area... some of which had black buildup in em), cleaning the pre-cat o2 sensor (which by the way made the o2 code for it go away), cleaning the electronic throttle body, checking for vacuum leaks and so on...

I was convinced it was in the fuel delivery. Early the pressure off the shrader valve seemed good (though I had no way of getting a pressure reading because of financial issues)... but then it just dropped off to a drizzle and I never got good pressure at the gas cap.

So that told me...

Fuel Pump (dead or broken)
Clogged fuel line
fuel pressure regulator
or something electrical with the fuel pump (wires, relay, etc).

I talked to a co-worker that had issues with his honda and that it was the fuel pump relay... which I had noticed before it wasn't one of the "obvious" under the quick cover relays and though maybe I didn't have one. But I did a little research... found out about the unobvious panel where the regular fuses are and pulled the relay and built a little jumper out of a strategically bent paperclip (which will forever remain as a backup

) and it fired up and sounded better than it ever did before. I drove it around a bit then had to head home for work.

Tonight I hit radio shack and picked up a 100 micro F and 22 micro F capacitors since nothing obvious looked bad and just got done soldering them in.

So I now know what the issue was and hopefully this will fix it.