I'm Original owner of my 1999 V70 with 300k miles and have an anomaly happening where I need the creative minds to help narrow down what part should I replace and in which order as every time I take it Volvo or to any other mechanic My Volvo doesn’t present herself with my issue. Frustrated but this car's engine runs excellently.

Consistent problem I'm experiencing:
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-tachometer starts to drop immediately below 1000 rpm and starts to sputter and then engine goes limp including power especially when I am slowing down to turn or a stop light.
-Only the battery light and the check oil light and the Up Arrow light displays on the dashboard when car goes limp.
-75% of the time if the tachometer starts to act up, I can safely pull over to stop and put the car immediately in park and just gun it to try to run gas through the engine and then it idles normal to allow me to go my merry way.
-If the car goes limp it will start up 50% of the time with no problem or I have to gun the gas for a few seconds and then it drives normally afterwards. I don't have to wait but today I had to wait about 10 seconds to start again but have to gun it to make sure the tachometer is running smoothly to continue to drive.
-I get NO Volvo codes (courtesy of the last 2 years replacing of various vacuum hoses and other parts)
-I may be driving with my foot on the gas pedal driving on freeway at a constant speed or a city street at 40 mph and then sometimes it feels the engine doesn’t know that I’m giving it gas and may drop by 5 to 10 mph for about a few seconds and then it recognizes that I still have my foot on the pedal and returns back to that speed I was going. (I recall my first experience of this about 2 years ago but didn’t think anything of it until this year where it’s happening often. So I’m thinking whatever is happening this is the major symptom that may be the causing the go limp shut down of the car when I slow down.
-I may pull out of my garage and then I would see the tachometer starting to go under 1000 and a little shaking occurs as if the engine isn’t getting any gas thought I may be pressing on the gas pedal. I put it in park and press on the gas pedal for a few seconds then it idles happily.
Other days, it happens then when I get down 100 yards and decelerate to turn right and the car goes limp with power shutting off.

I have replaced in the past 3 years:
Fuel Pump
Fuel Pump Relay
Both O2 Sensors (May 2014)
Air Mass Sensor (Feb 2015)
Installed latest software in on board computers from Volvo (Aug 2015)
Replaced vacuum hose under manifold (3/2013)
Replaced many other hoses that contribute to Evaporator Leak error codes along with a few smoke test to smoke out any holes from 2013-late 2014.

Had a retired Volvo mechanic check who had the tool/computer to check if my electronic throttle module is the culprit. After checking he said the ETM is not the problem. He suspected the ignition switch may be the culprit but I had that changed in 2008.
I talked to my former mechanic for 7 years in my former state and he suspects it is the Idle Air Control Valve. (When I called Volvo the part was $300. Can I buy an after market one)

I had a similar symptom with my 855T. Turned out to be the rubber air hose between the IAC (idle air control) motor and the intake manifold had a huge hole in it. Oil soaked and rotted away. Not easy to see but easy to feel. Don't know if this will work, but here's link to the pic. IAC and it's lower split hose.



Another slow=running problem was caused by the plastic vacuum tree that lives under the throttle bellcrank cover. The cover had worn a dime-sized hole in back of the tree, allowing a lot of un-metered air into the intake.

I don't know if any of this applies to your V70 but major air leaks can cause what you're experiencing as well as fuel delivery problems.

Replace your fuel filter lately? I did mine at way too late, at almost 180,000 miles, and the gas that poured out of it was as black as Coke. The fuel pump diaphram had dissolved.

Good luck,

Erwin

ETM Electronic Fuel Module If it is original it needs to go.
I did the Xemodex swap and been fine since.

My tank is usually fuel to eliminate lack of fuel but I will replace the fuel relay and others by using used pulled used parts to test.

Note there's 2 fuel relays.
one enables the fuel pump
one enables the fuel injectors
Both raise "you know what" when they fail or get flaky.

Your explanation has me wondering, what lights are on normally that fail when the tach acts up. be specific exactly what electrical items quit?
There's a number of items that can croak the engine, just a flaky ground at the
intake manifold for example. Making it important to notice as much as possible.

When it quits do you think it's lack of fuel? THEN the RPM falls?
Maybe one of the two fuel relays is crapping out?
Intermittent problems can be difficult to troubleshoot.

You can get some parts at the local salvage yard and save a bundle over dealer prices for items that may or may not be the culprit.

Bill

Hi Bill,

Here are further details:

1)1 out of 15 times when I am driving and then I slow down to turn at a street or pull out of my garage prior to braking to switch to Drive, the car completely shutsoff. The tachometer may right rough prior to completely turning off the car. The lights that come on as soon as the car is shutting off are the Up Arrow, Oil light and battery light. These lights never appear in my normal driving as my battery is recently new and my oil has been changed and I never use the 3rd gear (which I think that is why the up arrow is for).

It behaves like a lack of fuel when the tachometer goes erratic and then I quickly start pressing on the gas. It feels like electrical when the car shuts of completely when I am slowing down especially to turn at a street.

So I decided to go to my handy dandy Volvo dealership this morning since the past 2 days the issues has been more frequent then before (and they haven't figured it out as well but they haven't charged me either:).

First, the car hummed like a new car. No issues as I'm driving to the dealership which is 10 mins away. Then one of the senior mechanics hopped in the car and drove it. So he started driving fast and after a few minutes while driving on the roads (not freeway) he was able to feel a misfire of some sort. Then magically the 'check engine' light came up. I was excited.

After 2 hours back at the Volvo shop he came out and advise me of the following:

-Checked Fault codes ECM 150A air mass Flow sensor. Lower Limit.(**my comments- I just had the AMF replaced brand new in February for the same thing that I am experiencing now by another shop**).

-Checked the Fuel Pressure is at 45 PSI. Check for vacuum leak and PCV systems is in OP. (***The volvo mechanic said it would be good to perform the PCV service for all intake hoses but not now***)

-Checked and Cleaned the ETM. Throttle Body and it passed the test with no issues.

-Check the Spark plugs look ok.

-Check and replaced Air filter since it was dirty.

-Found the Fresh air door is not opening which needs the Air box to fix. I opened the door temporary and see if it takes care of the running issue. Recommend PCV Service if it still has the running issues. (**Mechanic either force this door open for now to see if this may be the culprit**).

I just drove the car on the freeway in the heat of the day for a couple of hours and no problem so far. However, I'm not optimistic as this is only a guess for now. My long term mechanic who is out of state doesn't believe this door or the PCV will resolve the problem.

I have never changed the PCV or ETM in my vehicle.

That's a detailed report for sure.
There's a basic problem in trying to diagnose an intermittent, that they can say
there's fuel but that doesn't mean that fuel didn't quit to cause your car to quit. They can check pressure at the rail and it's fine but I'm still wondering
about your main fuel relay, since it shuts down power to the injectors AND the MAF. Perhaps the ECU threw a MAF code only because it lost power. Did you get to
keep the old MAF? You could swap it back in and see if things are the same.

My strong hunch is to swap that fuel relay. Probably all the older cars should get a new one.

It's 2/32 in the 850 and mounted above the radiator on the drivers side. Maybe the same setup in your car, I don't have the wiring diagram. I've pondered swapping out the Fuel relay as a routine service item, maybe so many miles or years since they can't fail or get flakey and have the car run. This is what they used to call the RSR (The Radio Suppression Relay, that was a misleading
name since it has zero to do with radio's and everything to do with enabling the fuel injectors) and a constant recurring headache in high mileage cars.

I thought also about the Cam position sensor, but I'm uncertain since maybe that would throw a code to help diagnosis. Maybe others can chime in on that. I also wondered about your ignition switch but that's unlikely if you get the check engine light.

Post back with any results, and good luck, Bill