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Intermittent engine performance, rough idle and stall


I have a 2005 Volvo XC 70. For the last six months or so I am experiencing a very intermittent issue. Every once in a while the car starts to idle rough but then it returns to normal, sometimes while driving, even on highway, the car looses power, as if it ran out of gas but than, after a a couple of seconds, things return to normal. Last week, things got worse, as soon as the engine turned on, it ran for about 10 seconds and then it stalled. I ended up having to tow it to my mechanic but by the time the mechanic got to working on it, (it was the weekend so it was about two days later), things somehow miraculously returned to normal.

All diagnostic tests point to fuel related issues (low fuel pressure, etc; can’t really remember them all) but, given the fact that the issue is so intermittent, there is no clear diagnosis so far.

I changed the throttle body, air mass sensor, fuel pressure sensor and fuel filter so far but nothing really helped.

Any ideas would be much appreciated.

Intermittent problems can be an absolute headache to try to diagnose. I ran into one wherein the car would sputter intermittently under load, but usually not. It turned out that the car had a slight rod bearing knock and when under load, when the knock was bigger, the knock sensor was detecting the pulse and registering it to the ECU as if it were a spark knock. The ECU would then back off the fuel and ignition timing, creating havoc.

I am NOT suggesting that this is the cause of your problems as well, just pointing out how complicated intermittent problems can be on modern engines.
Do you have any other symptoms whatsoever, even if they seem unrelated?
Did you get a Check Engine Light? If so, do you know what the codes were?
Did the mechanic try anything? Checking any sensors, testing the fuel pump, checking the injectors, anything?
How many miles does the engine have on it?
When was the last maintenance done (new spark plugs, filters, etc.)?

The shop may be able to temporarily install a fuel pressure gauge that you watch while driving. If it falls right when you notice this problem occurs, they’d at least know it is caused by a rapidly falling fuel pressure. Once they knew that, they could get to the bottom of it pretty quick. The fuel pressure isn’t supposed to ever fall like that. Things that might cause that are faulty fuel pump relay, faulty fuel pump wiring, faulty fuel pump, dirty fuel filter, etc.

Or if the symptom occurred and the fuel pressure remained steady, that would be a big clue too. Ask your shop if they have the capability to do that. The other option is to leave the car with them, rent one for yourself, and ask that one of the techs there use your car as a daily driver. Eventually it will fail and the tech will be able to figure it out.


The issue turned out to be a corroded fuel pump electronic module. The electrodes/connector was totally corroded which I guess explains the intermittent nature of the problem. It has been replaced and everything is back to normal; no check engine light, no rough idle.

Thanks for all the input!


Thank you sincerely for your follow up post.

You should know that you’re not alone. Some years back a class action lawsuit was filed against a particular refiner for excess sulpher in their fuel eating up the connections on the fuel pumps.

Thanks for the posting the final solution. It’s a little unclear, was the part that failed inside the fuel tank, part of the pump ass’y in other words, or something outside the fuel tank?

Your post makes me think another idea for diagnosing problems like this, easier to implement than a fuel pressure gauge the driver could watch, would be a simple volt meter connected to the fuel pump power line. You’d have likely noticed the voltage drop when the symptom occurred.

Well, I spoke too soon. After the initial relief of thinking things got finally resolved, this morning I had the exact same symptoms back as before and at this point the car is actually un-drivable. My mechanic said he is going to tow it back to the garage tomorrow.

The saga continues, I will keep you posted.

If your shop guy runs out of ideas, ask if they could temporarily install a volt meter connected as close to the fuel pump electrical input contacts as possible so you could watch the readings as you drive. If the problem is the electrical supply to the fuel pump, you’d soon discover it this way.

Years ago I had a VW Rabbit that would have this symptom intermittently, stall while driving, and it turned out to be a burned out relay plate connection. The relay plate where the fuel pump relay installed. They had to install a bypass wire there to jump around the bad connection. When that connection failed it would cause a loss or lowering of electrical power to the fuel pump.

If that turns out to be the case, it can be caused by a flow restriction in the fuel line, like a clogged fuel filter. That puts extra load on the fuel pump and increases the current through the connections, which can corrode or burn them.

@the_same_mountainbik, to answer some of your questions:

  • Do you have any other symptoms whatsoever, even if they seem unrelated? Well, one strange thing I noticed about a year ago; a strange hair-like substance started to come out of my muffler. Initially I thought it was a prank by the neighbourhood kids or some animal got stuck in there but it turned out it is not all that uncommon, it is the inner fiber glass insulation of the muffler that got loose and is slowly being discharged via the pipe. I was thinking, can it be that somehow it got into the way of the exhaust and choke the engine or maybe affected some of the sensors that might be in that area (not sure what the exact anatomy of a muffler is). I mentioned this to my mechanic but he didn’t make much of this.
  • Did you get a Check Engine Light? If so, do you know what the codes were? The engine light is on constantly, but I don’t have the actual codes with me. My mechanic punched in the codes after he hooked up with his scanner, what came up was fuel pressure sensor, fuel filter, fuel pump, air mass flow sensor, and a couple of other things which I don’t remember, but all seemed to have pointed in the fuel system direction.
  • Did the mechanic try anything? Checking any sensors, testing the fuel pump, checking the injectors, anything? He checked the fuel pump and he thought that was OK but that was about it.
  • How many miles does the engine have on it? about 130K
  • When was the last maintenance done (new spark plugs, filters, etc.)? Hm… Actually, apart from the oil change, there was no real maintenance done on the car ever since I owe the car (since 2008). The mechanic did change the air filter though.

Thanks once again.

I have an 03 Ford Explorer and had the exact same issues you are having. My issues ended up being a blown head gasket. and because of the timing setup on the Ford 4.0 it was cheaper to change the motor. what was going on was compression was leaking from piston to piston. i hope this is not what your issue is, but it is something you can bring up to the one working on you car.