Odd idle surge coming back to idle...2001 V70 T5 Topic is solved

Post by **Gymbo** » 17 May 2016, 12:10

I have a 2001 V70 T5 with 212K. I got the car last September and it has been fantastic apart from one mild driveability issue. It has always has a hiccup or surge when driving down a slight decline with light throttle. It had a new transmission installed by a Volvo dealer last July.

Another thing I've noticed is when I turn the climate control to Auto it has a drop in idle speed and slight stumble every minute or two. It goes away when I turn back to manual climate controls with the AC off.

Now recently I am experiencing is a drop of idle and stumble as I take my foot off the gas to brake in traffic. It drops the idle, stumbles and then returns to a smooth idle. Although I am beginning to pick up a very mild version of the same behavior it has had with the AC on.

It's generally running ok, not throwing any codes, idles smooth, other than the mild issues above, has good power, and is getting usual fuel economy.

So...I am running through a diagnostic checklist. MAF? ETM? Battery? Anything else?

I used MAF cleaner spray on it on Saturday...no change. I unplugged the MAF, and drove to work this morning and I think it made it worse...with a bit of delayed weird throttle response off idle.

I am wondering about my battery and charging system...I know low voltage can cause all sorts of weird issues. I have 12.9 V at the terminal in the engine compartment with the engine off. I haven't checked it with the engine running.

I am thinking it's most likely the ETM....but would appreciate any input. Thanks!

Post by **abscate** » 17 May 2016, 14:48

The ETMs generally fail safe and fail hard. Once the ECU doesn't like the inputs it's getting from the ETM, it goes into limp and trips the ETS light

Post by **Gymbo** » 17 May 2016, 16:53

abscate wrote:The ETMs generally fail safe and fail hard. Once the ECU doesn't like the inputs it's getting from the ETM, it goes into limp and trips the ETS light

Yeah, it's not doing that. Just a cyclic stumbly idle and a stumble when it initially drops to idle. It feels like it's almost going to die as it comes back to idle then idles pretty normally.

c70_lindsay · Post by **c70_lindsay** » 17 May 2016, 16:58

I am having similiar problems with my 99 S70T5, keep an eye on my post. Your symptoms are how my problems started, still trying to work it out. Good luck!

Post by **Gymbo** » 17 May 2016, 19:52

Here's my latest diagnostic experiment.....after work the car idled rough immediately after starting. I turned it off and restarted and idled like normal immediately.

After driving home from work with the car in my flat driveway in Park, I revved the engine to 1500 RPM and let off the throttle and it stumbles, drops to idle stumbles once and then idles like normal. It's 80° out and it seems to run worse as it has been getting warmer out.

I am also going to go to the auto parts store and have my alternator output tested. Will I need to get access to the battery or will the positive terminal in the engine compartment suffice?

Post by **abscate** » 17 May 2016, 22:10

Battery connection is fine for alternator test.

Before spending any money on major parts, do a slow systematic inspection of your hoses, following each one, removing and replacing ends. A small vacuum leak can cause the same stumbling.

If you just " look at the hoses" you won't find anything.

Post by **Gymbo** » 17 May 2016, 23:36

abscate wrote:Battery connection is fine for alternator test.

Before spending any money on major parts, do a slow systematic inspection of your hoses, following each one, removing and replacing ends. A small vacuum leak can cause the same stumbling.

If you just " look at the hoses" you won't find anything.

That's a good idea. I was just out looking at all the vacuum hoses under the hood and giving them a finger check.. There's a fair number of them. I need to find a vacuum hose diagram.

The battery voltage is 12.9V with the engine off and 14.2V at idle.

Post by **abscate** » 18 May 2016, 11:53

Good numbers for battery and alternator.

Under hood sticker got that hose diagram...maybe up near driver position, low on hood?

Post by **Gymbo** » 20 May 2016, 18:33

The latest wrinkle is the last couple of mornings it seems to run really well when the air is cool and runs noticeably worse in the afternoon when it's been around 80°.

Not sure what to make of it, but that's what it's doing.

Post by **Gymbo** » 23 May 2016, 23:14

Could a bad gas cap cause this? I just got a CEL and P0455 Large Emissions Leak - the code reader suggested bad gas cap.

Upon further reading, a purge valve could do this too....