Thump when slowing down
 

Hi Guys and Gals,
my apologies for being wrapped up in my little world almost exclusively of late.

My 3.7 FL 40v has developed a thump coming from the trans when slowing down normally, I also seem to have fluctuating tickover.
I have read somehere that the thump is caused by the MAF sensor, is this correct? Something to do with it sending the wrong signal to the Torque Converter?
Could any of you Gurus out there shed some light on this? As I won't drive the car until I have effected a cure.

Thanks in anticipation,
Steve

Hi Steve
Have you tried a VAGcom scan?
MAF errors normally show up so at least that would be a starting point

Hi Guys and Gals,
I have done vagcom on my poorly blue boy, (though the chauvinists might say HE is really a SHE!)
below is an engine read out, I can also hear air (sounds like induction leak) at idle.
Also at idl;e there is the faintest hum of fuel pump, which makes me think I have acombination of problems, possibly a perished hose, and a fuel pump on the edge of dying. Your thoughts, as always are appreciated!

16514 - Oxygen (Lambda) Sensor B1 S1
P0130 - 35-10 - Malfunction in Circuit - Intermittent
17536 - Fuel Trim; Bank 1 (Mult)
P1128 - 35-10 - System too Lean - Intermittent
17538 - Fuel Trim; Bank 2 (Mult)
P1130 - 35-10 - System too Lean - Intermittent
17544 - Fuel Trim: Bank 1 (Add)
P1136 - 35-10 - System too Lean - Intermittent
17546 - Fuel Trim: Bank 2 (Add)
P1138 - 35-10 - System too Lean - Intermittent
17549 - Load Calculation Cross Check
P1141 - 35-10 - Implausible Value - Intermittent

Readiness: 0000 0000
Best Regards to all,
Steve

Could be Oxygen Sensors or MAF steve - for example

17536/P1128/004392 - Fuel Trim; Bank 1 (Mult): System too Lean

Possible Symptoms
Malfunction Indicator Light (MIL) active

Possible Causes
Mass Air Flow (MAF) Sensor faulty
Oxygen Sensor Control faulty
Oxygen Sensor(s) faulty
Fuel Injector(s) faulty

Possible Solutions
Check Mass Air Flow (MAF) Sensor
Check Oxygen Sensor Control
Check Oxygen Sensor(s)
Check Fuel Injector(s)

Hi Neil,
thanks for that, informative, but, NO MIL light on, symptom is engine running lumpy,(sorry, forgot to mention that) not as responsive from idle so, idle, foot down, pause and then revs, with a large amount of hissing. I'm fairly sure I have some split vacuum hoses, which would also probably fit the majority of symptoms, mix weak, on both banks, O2 sensor actually reading correctly as the mix is lean due to the ingress of air.
Will try this first, as replacing the vacuum hoses was high on the hit list anyway!

Will report back when time allows me the opportunity of swapping the hoses.
Many thanks to all.
Best regards,
Steve

The MIL light is only a possible symptom, its possible to have a duff sensor with no light showing.

The light will only come on once the sensor starts giving readings outside the expected range.

A faulty sensor can still give readings within range but the wrong readings which could result in fuelling issues. For example on a cold day, it could tell the ECU that its warmer and the result could be lean running

Vacuum pipe issue? Pop the covers off and check that the vacuum pipes around the back haven't given up the ghost.

Thanks mannyo and psyche,
TBH, the vacuum pipe replacement was so "up there" on the list of things to do, that that roll of replacement pipe is actually in the boot!!
Hoping for some spare time through the festivities to get a go at it.
Many thanks one and all.
Best regards,
Steve

Hi Guys and Gals,
I'm pleased to report the "thump" has now disappeared, after I replaced the small vacuum lines, and removed the PCV through which I cpould hear was an air leak, subnsequent dissembly revealed a diaphragm in two halves, so two questions, does anyone have a spare?? I don't want to go to the stealers, as the valve is £74!!!! Failing that I will be in contact with our sponsors, fine body of men they are!!
Later on, I may try a repair to the diaphragm, possibly bonding a condom to the existing halves, as it is an all but circular split. I have seen this repair before on motorcycle CV carb diaphragms.
I suppose the moral of the tale is, before you spend big dollars, have a check around using some old fashioned nouse!

Best regards to all.
Steve

Hi Guys and Gals,
further to this, the intake is now plugged, and I'm awaiting delivery of the new valve. I have done a vagcom scan, and I'm free of DTCs!!!(Hooray!!!)
Interestingly, using vagcat online, I obtained the part No for the valve, and asked TPS, this reduced the rate to £54+ VAT, I then googled it, and was astonished to find that AMAZON could supply it, from the USA, at £49 inc VAT and delivery!!
Just thought I'd share....!
Best Regards to all
Steve