Hesitation / surging at high speeds

geekman · 4 Feb 2013 at 18:15

Think I may have an issue with my car (Volvo 850 T5).

I'd previously blamed it on loss of traction, but after replacing tyres and suspension components the problem is still there, and appears to be getting worse.

Basically, if I put my foot down at a low speed, say 20MPH, and keep it planted until say 70MPH, the car accelerates rapidly and pulls strongly - no hesitation, juddering or strange noises.

However, above 70, for instance if I'm accelerating from 70-100, the car judders and shakes, as if the power is being switched off and on very quickly.

After keeping your foot planted for a while, it sometimes picks up, sometimes not. The needle on the boost gauge wobbles as well, whereas when accelerating at lower speeds it stays steady.

I had intended to post a video to demonstrate what I'm talking about, but I don't want to get into trouble with the law so I'm afraid my crappy description will have to suffice.

I have limited mechanical knowledge, but I assumed the issue may be damaged hoses or even a dying turbo? If anyone could point me to possible causes of the problem it would be much appreciated

Many thanks.

Brookert · 4 Feb 2013 at 18:19

If your engine has a maf, disconnect it and go for a quick spin. It will quickly highlight whether it is a problem or not.

geekman · 4 Feb 2013 at 19:03

Brookert said:
If your engine has a maf, disconnect it and go for a quick spin. It will quickly highlight whether it is a problem or not.

I believe it does, and as my lambda light comes on occasionally that could well be the problem. Just went out to have a look and I can't seem to find the maf, or indeed the plug, any idea where it may be located?

Brookert · 4 Feb 2013 at 19:06

geekman said:
I believe it does, and as my lambda light comes on occasionally that could well be the problem. Just went out to have a look and I can't seem to find the maf, or indeed the plug, any idea where it may be located?

find the airbox, it is normally located just after that, or between it and the intake manifold somewhere. You'll see a connection going into the piping.

geekman · 4 Feb 2013 at 19:10

Brookert said:
find the airbox, it is normally located just after that, or between it and the intake manifold somewhere. You'll see a connection going into the piping.

That's what I was looking for, but I can't seem to find the airbox - I'm utterly useless at mechanics and have never really done anything like this before. I've got a picture of the engine here if it helps?

GinG · 4 Feb 2013 at 19:19

Could the problem be the airfilter?? Heatsoak may have a bit of a issue.

Brookert · 4 Feb 2013 at 19:22

See that cone filter thing on the right? The connection just after it, thats your maf. Unplug the electrical connector (not the tubing!) but do it carefully.

geekman · 4 Feb 2013 at 19:59

Brookert said:
See that cone filter thing on the right? The connection just after it, thats your maf. Unplug the electrical connector (not the tubing!) but do it carefully.

Right, I've done it, thanks! Just about to go out and I'm bringing a friend with me to video any possible noises etc

geekman · 4 Feb 2013 at 20:57

Just got back, and have taken some videos which I'll upload later when my internet is less useless. I'd also like to apologise to anyone who happened to be on the m25, I don't normally drive like a ****

Anyway, once I unplugged the MAF the lambda light came on straight away. The car felt down on power, but in general accelerated smoothly at any speed, although there were still a few blips where it stuttered a bit. Nowhere near as much as usual though. The blips were in general at the upper end of the speeds I reached.

I did another run with the MAF plugged back in, and interestingly the lambda light stayed on. It now felt back to full power, but didn't judder or hesitate like it normally does, again there were a few small blips but nothing serious.

So, would the consensus be MAF-related issue then?

thepharcyde · 4 Feb 2013 at 21:18

Get some electrical cleaner spray on it.

geekman · 5 Feb 2013 at 07:58

thepharcyde said:
Get some electrical cleaner spray on it.

Should I spray it all over the MAF itself as well?

Jonnycoupe · 5 Feb 2013 at 10:06

If its a dirty MAF then that aftermarket cone filter is probably to blame.

Paul. W · 5 Feb 2013 at 10:12

I'm just waiting delivery of my new MAF and standard air filter. Last owner fitted a K&N Panel filter and im sure thats to blame.

Exactly the same symptoms as your car btw. I proved it was my MAF though from reading the codes.

MAF's aren't cheap either, especially for Bosch ones. Mines around £70 and thats including carparts4less discounts and money off for returning my old one!

geekman · 5 Feb 2013 at 10:48

Paul. W said:
I'm just waiting delivery of my new MAF and standard air filter. Last owner fitted a K&N Panel filter and im sure thats to blame.

Exactly the same symptoms as your car btw. I proved it was my MAF though from reading the codes.

MAF's aren't cheap either, especially for Bosch ones. Mines around £70 and thats including carparts4less discounts and money off for returning my old one!

I think my MAF is a bit cheaper than that, but I'd rather clean it first and see what difference that makes, especially as I don't want to buy a new one and have that ruined by the air filter!

Is there anything I should do with the air filter short of replacing it? Should I clean it or anything?

rodenal · 5 Feb 2013 at 11:16

Just get rid of it tbh, you could try a heatshield for it and a cold air feed but tbh other than making noise and potentially ruining mafs they're pretty useless.

geekman · 5 Feb 2013 at 11:27

rodenal said:
Just get rid of it tbh, you could try a heatshield for it and a cold air feed but tbh other than making noise and potentially ruining mafs they're pretty useless.

I can't simply remove it though can I? Or is it just a bolt-on kind of extra which doesn't replace an actual component of the car?

HummuH1 · 5 Feb 2013 at 11:30

geekman said:
Should I clean it or anything?

If you keep it, yes you should. You can get cleaning kits for cone filters. Chances are it hasn't been cleaned and oiled in ages. The oil is important to help the filtering. Don't over oil though as it can cover the MAF in oil, which is another potential cause of MAF issues.

HummuH1 · 5 Feb 2013 at 11:35

geekman said:
I can't simply remove it though can I? Or is it just a bolt-on kind of extra which doesn't replace an actual component of the car?

You would need to replace it, most likely with an OEM intake (plastic housing and panel filter and more than likely a cold air feed from underneath the bonnet).

You might not be able to fit it all back in though. Looks like your hoses have been changed from OEM and they might have put a cone filter in there as the new hoses conflicted with the intake system.

Best bet would be to find one at a scrappy, should be cheap and check to see if it will fit. If it does, get a new panel filter and re-fit. It should be very straightforward.

Take care when handling the MAF at all times, it takes very little to fubar them.

HummuH1 · 5 Feb 2013 at 11:43

Think this is your engine in OEM form:

You can see the black plastic filter housing where your cone is. Looks like it should fit back in OK but you'd need to check.