2006 C5 2.0 16v diesel pulsing throttle.

[MFHBlueberry]

At gentle throttle openings the engine pulses like I’m constantly pressing and letting go of the accelerator. It does it on cruise control too. It’s only very gentle but it irritates the heck out of me.

Any ideas?

[GiveMeABreak]

If it gets any worse it will disengage the cruise control and throw a wobbly.

Get it read with Lexia to see if there is a fault code. If not there may be before long. Check air hoses for the smallest of leaks, but if the hesitation gets worse the fault may develop, which you may have to wait for it to do to ascertain a fault code.

[Bob_V]

I had that with my 2.0 2007 C5 estate. I was at the point of taking it into the garage for it to be investigated but I had a motorway trip coming up so I left it. During the trip I had occasion to give it an italian tune up due to some idiot in the middle lane. I gave it a real blast on the throttle. Looking in the mirror I saw a big cloud of black smoke coming from my exhaust. I did it several times during the trip. Each time the smoke was less than the time before. Eventually no smoke on a fierce acceleration. The next day I noticed that the hunting had gone away. To this day it has not returned. I can only assume that there was some crud somewhere in the system which was causing the problem. I make a point now of giving the car the occasional blast just to see if there is any black smoke. It worked for me so why not give it a try.

Bob

[Paul-R]

Smoke just shouldn't happen on either a 2007 or 2006 car as the FAP is there to catch all the particulates. Is it possible that the 2007 car had been defapped?

[Peter.N.]

I had a 'hunting' problem with the previous model with the 8 valve Hdi and it was due to the pressure regulator on the back of the HP pump, don't know if the 16v uses the same one.

Peter

[MFHBlueberry]

Next time I go out I’m going to try disconnecting the maf sensor to see if it has any impact.

[MFHBlueberry]

Disconnecting the air mass meter had cured the problem. Might there be any detrimental effects from running with it disconnected for a week or two as I can’t afford a replacement just now?

[GiveMeABreak]

The engine ECU relies on the information from the MAF to determine the correct fuel to air ratio. Disconnecting the MAF will result in either too much air air (lean running) or too little air (rich running). Neither of these are good for the engine and can cause rough idling / stalling and smoking issues. So don't leave it for too long. It would seem your MAF is faulty - but try cleaning it with some MAF cleaner first - although be very careful not to damage or touch the MAF sensor wire - it is very sensitive and can easily be damaged or contaminated. Spraying MAF cleaner onto it can perk it up.

[MFHBlueberry]

I gave it a good blast with Maplin (rip) contact cleaner which I once used on a MAF from a Yaris to good effect, but in this instance it made no change.
I guess I need to raid the back of the sofa for some cash... There seems to be a wide range of prices out there, are there any brands to avoid?

[myglaren]

VDO is the one to look for.
Siemens was the OEM and VDO was spun off from Siemens.

Cheap ones are generally a disappointment.

[GiveMeABreak]

Absolutely - try and go for a genuine one from a dealer having a clear out.

Pop your VIN up here if you want the part number.