2002 S60 AWD rough start won't run except at full throttle

[jeljm]

Good morning. I'm almost certain I know what this is. The trick is the reasoning behind it. So without further delay I'm fairly confident this is a massive vacuum leak potentially a failed intake manifold gasket.

When I first replaced the pcv system on my v70 I made a mistake and didn't get a good seal on the intake manifold. The car started right up then immediately died. I could only get it to run if I gave it some gas. I could even drive it but due to the lack of vacuum I had no brakes. I also smelled gas because the fuel injectors fire fuel right next to the joint between the manifold and the head. The fuel pooled and then spilled out causing the smell of gas. The reason I suspect it runs at full throttle is because the ecu doesn't expect a vacuum in a turbocharged car. It's looking for pressure. I suspect there'd be a sweet spot right where the turbo is putting out close to atmospheric pressure.

So long story short. Check for huge vacuum leaks likely near the intake manifold (because of the gas smell).

Good luck.

[witenite]

MadeinJapan you hit the nail on the head. I disconnected the MAF and it ran like a dream. Most cars won't run with the MAF disconnected but mine ran great. I replaced it and am back on the road.
Only thing is why did Bosh use security screws to hold the sensor in place?
Again thanks everyone for all your help. I really appreciate it.

[jeljm]

Hey that's great glad you got it. I'm a little disappointed I got it wrong. In my experience the engine will idle without MAF but then die suddenly when you give it gas.

[01_Nautic_V70]

witenite, glad to hear you are up and running again. Did you save the old MAF? I had a MAF problem but was able to get it running again with a can of MAF cleaner. May want to try cleaning your old one and setting it aside as an emergency backup.

[abscate]

Here is what happening on Volvo.

MAF connected...the ECU measures the air flow via the MAF and meters fuel precisely based on that measurement. One loose clamp letting in un metered air and the fuel air balance fails, usually to a no-start and/or poor run.

Disconnected the MAF...the ECU finds no signal and defaults to a lookup table of fuel vs rpm. This usually works pretty well as the total air coming is pretty matched to rpm, do the car runs pretty well.

The erstwhile mechanic thus concludes the MAF is bad, springs for a new one, and then gets the familiar, wretched taste of bile in the throat when the car won't run and the non-returnable MAF giggles at the drain it put on your bank account.

The Mechanic Vos Superium, however, has read the threads and searches for, diligently, with verve and elan, finding the loose hose, tightens it, and boosts the 5 speed off into the sunset.

[witenite]

01_Nautic_V70 I did try to clean it before I bought a replacement but it did not help. I had to return the old one for a core deposit so I hope this one lasts longer than the car

[MadeInJapan]

Glad I was right- that's rare these days it seems as more people with more experience than me!

I have a friend with an '06 XC70 I'm going to go and help him with today. His wont' idle but as long as you keep a foot on the gas, it goes...and no check engine light on the dash..
I'm taking with me, new spark plugs (has no idea when they were changed- at 200K miles now)... a MAF sensor replacement, a code reader and a rubber glove to check PCV pressure... Not sure what the issue is but between tools I have and extra parts, I think we'll be able to figure this out.
On a side note- all service records from the dealer- no tranny flush... 7500 mile oil changes with dino oil and who knows if PCV was ever done...timing belt at the 120K mile interval...