Hi all,

Got some issues with my 99 C43 / 5.4ltr.

First off, cold start is not real good, seems like its lean on fuel at start up, but only for the first start. If you shut it straight off then start again, its fine.

Secondly, it seems to have a bit of an off-idle hessitation that makes it difficult to drive smoothly at low speeds.

Third, there is a rattle at idle that goes away as soon as you touch the throttle, appears to be coming from timing chain, but cant seem to narrow the sound down to one side or the other. Does this with belt on or off.

Forth, it seems to be losing low down torque, up higher in the revs it seems reasonably good, not what it should be, but floor it off the line from a standing start id expect easy wheel spin, 18 months ago it would spin off the line at about 1/2-3/4 throttle.

If the traction control cuts power at low rpm for wheel spin, the power comes on very strong and seems a lot better than if it is a straight up punch the throttle with no traction control intervention, not sure why this is.

I have replaced the following items over the past 18 months:
- Timing tensioner
- plugs 40,000klms ago
- plug leads ( factory OEM kit )
- coolant temp sensor
- cam sensor
- crank sensor
- MAF ( 3 weeks ago, genuine OEM )
- intake manifold gaskets
- variable runner vacuum hose
- throttle body gasket
- rubber hoses between intake and rocker covers
- pedal position sensor
- rocker cover gaskets
- water pump
- fan clutch
- idler pulley
- tensioner pulley
- MAF intake elbow rubber seals
- fuel pump
- fuel filter
- radiator
- ESL
- O2 sensors ( genuine Bosch )
- Lateral accelorometer ( silver one in the boot )
- transmission electrical connector

There may be a couple other items i have replaced that ive forgotten.

I have not replaced coils or knock sensors, but coils have been removed and put back in different spots before with no change.

what could cause this thing to seem down on power the way it is? Could cam timing be out due to worn parts?

No codes any time ive had it in to the workshop, but this being a Euro spec car there is no check engine light either.

ive not had the chain off at any point, i doubt its even been off.

no, it wasnt seperated. If i hold my hand over the MAF while idling, the engine dies pretty quickly and does not seem to lose the vacuum very quickly there at all, even though my hand does not make a real good seal.

its brand new and from a sealed Bosch box, there was a minor improvement over the old one it replaced. But only very minor.

Mine was not that bad before, old MAF was pretty ok.

if i had a vac leak big enough to cause an issue, wouldnt it lose vacuum quite quickly after the engine shuts off with my hand over the intake? It just seems to me that it is holding vacuum quite well.

The rattle sure seems to be coming from up the front more so than anywhere near the exhaust, but ill check that out.

All i read seems to suggest the chain guides are pretty much a life time part and dont really cause issues, the chains seem to be mixed opinions, there are lots saying that the chains are no issue, and just as many saying theyve found them stretched to buggery.

If the chain was stretched and cam timing was out, would this in turn directly affect spark timing? Is spark timing triggered by cam sensor or crank sensor?

Would this rattling noise be causing timing retardation due to knock sensors picking it up?

If not the cam chain what else would cause this rattle that goes away with a 100-200 rpm increase?

You Tube

How much influence does the transmission control unit have over off idle hessitation and surging at low RPM slow take off?

mine is not that loud, its noticable, but goes away with as little as a couple hundred RPM above idle.

I replaced the majority of them, and theyve all been checked a few times, theyre done right. I did 11 years working on Corvettes and made quite a few of those run smoothly.

The issue started coming up before i had the intake manifold gaskets replaced by a workshop with brand new genuine Merc parts. When they did this, they pulled the vac hose out for the variable intake flaps and replaced it with one that was too small to fill the hole, against my advice. They sealed around that with silicone, which made the car run perfectly smooth for about a week. They then took the manifold back off and replaced the hose with a much fatter one, and sealed around that, although apprently the hose is a snug fit. The issue has been there since just after this.

The gaskets were reused, they had only been in 4 weeks.

the intake has been opened up before, but not by me or the shop i use when i dont have time to do these jobs.

Can you tell me how you did that? The diagnostic port is under the bonnet on the passenger side.

Did the knock sensor code go away after turning off the engine?

what is the part number for the knock sensors?

Thanks mate, i aint taking the bonnet off!

What was your reason for using the M156 knock sensors?

Does anyone have any info on any sort of diagnostic equipment i can buy for a Euro spec car that will allow me to check most modules?

Are there any around that i can make changes to the settings within the ECM?