sluggish acceleration (feels like there are 3 AC condensers pulling on engine)

**mikeymike54321** · 07-12-2017, 09:47 AM

2004 - XC70 - 225,000 miles - has newer fuel pump - after the car has warmed up it feels like there is something weighing the engine down as if there are extra AC condensers turned on. there is a barely noticeable vibration on the throttle pedal that accompanies this behavior. car is throwing no codes. fuel pump, alternator, and ac condenser all ok. shifting fine. it had been throwing a catalytic converter code 6 months back, I thought it was maybe a clogged CC, but again no codes currently. maybe the MAF sensor??? it is possible that the sparks plugs need to be swapped out??? looking for an assist, this one has me stumped.

**Astro14** · 07-12-2017, 12:18 PM

Bad MAF rarely throws codes and it would be my first guess...but since we're guessing, I would work cheap to expensive and stop when. The problem goes away. So, start with new plugs.

Then clean the ETM.

Then try a MAF. Get a Bosch off Amazon. Volvo wants some crazy price.

A bad MAF can cause exactly what you describe. It's drive by wire, so the throttle won't open more than the computer thinks it needs to and the injectors won't put in more fuel than the MAF measurement determines.

But that's a guess...and I hate guessing...

**mikeymike54321** · 07-12-2017, 01:08 PM

thanks for the advice. the ETM was thoroughly cleaned 1 year ago. I will get some new spark plugs,,, and MAF if necessary.

**JRL** · 07-12-2017, 02:58 PM

You could have a bad/failing coil that is just starting to go bad under a load and when it gets hot

**mikeymike54321** · 07-12-2017, 04:47 PM

Would the coil start to fail and no codes thrown?

**Astro14** · 07-12-2017, 05:48 PM

Originally Posted by mikeymike54321

Would the coil start to fail and no codes thrown?

Maybe. A coil failure generally (not always) manifests itself under load as a miss, which sets a code.

But you could have a misfire from a failing coil that the ECM didn't recognize. In which case, no code.

How long have you owned the car?

When I get a used car, I "baseline" it: all new filters, fluids, belts and spark plugs. I can see tires and brakes, so they get replaced when needed, but the fluids, filters and plugs are usually of unknown age, so it's easier to replace all that and know where I am starting from...back in the day, I would've included cap, rotor, and plug wires, but those parts don't exist on anything I've bought lately, so, I don't include them any more...

**vtl** · 07-13-2017, 07:30 AM

What catalytic converter code did it throw?

In ideal world at this mileage the car should have been running on a third set of oxygen sensors

Front HO2S is crucial for engine computer, this is its primarily feedback sensor. The sensor needs to heat up before it starts to report correct value, this is why few first minutes after cold start ECU is preparing fuel-air mix according to internal tables, with slight fuel overprovisioning to prevent H2OS and converter from burning up. Then, when the sensor is hot, it switches to HO2S readings. At this moment, if the sensor is dead, you car may start running weak or even rough.

**GearheadTool** · 07-15-2017, 11:55 PM

Originally Posted by JRL

You could have a bad/failing coil that is just starting to go bad under a load and when it gets hot

How would he test that?

**VolvoXC70NO** · 07-28-2017, 03:28 AM

I've had 3 coil failures. All of them threw error codes. But you didn't need an error code to know something was up. The engine misfired like crazy under acceleration and even idle was really rough and the whole car shaking. The coil failures stopped when new sparkplugs were inserted. Worn sparkplugs will kill coils. Something about the current drawn, I'm no electrician..
To test it: Do some hard accelerating. Normally it's noticeable the instant the automatic does a kick-down.

Mine improved acceleration when I replaced the TCV valve and fuel filter aswell.

MAF sounds like the most likely culprit if there's no error code. Had a VW Passat TDI with defect MAF, it had no acceleration whatsoever. Full throttle or no throttle in 4th and 5th made no difference.

**mikeymike54321** · 08-01-2017, 12:02 PM

Thanks for the great info all!! much appreciated! I finally got around to replacing the spark plugs, and that seems to have helped some, but there is still some drag on the engine. I am going to replace the MAF next and see what results that yields. While swapping out the plugs I noticed some oil around the coils, I am replacing the oil filler gasket tonight, and making sure the PCV is clear/unclogged.