lumpy idling and power loss 2.0 Petrol

[tempragolf]

My 2.0 petrol (1999) V reg. It idles around 600-650rpm and is lumpy. Acceleration is poor. If I am in 2nd or 3rd and floor the throttle it is sluggish but never misfires. Also, when I am driving along and take my foot off the throttle I feel a very slight jerky movement - very slight. I have had the car for 3 weeks, its covered 97K, had the cam belt replaced on the third day for safety, changed the plugs (Bosch 4 electrode ones), oil and filter changed but have't changed the fuel filter yet! I love the car and the way it feels to drive. Any ideas on where my problem may lie, please?

[teamster1975]

Welcome tempra!
Have a read through this post, it may be of help.

[mjb]

Also, when I am driving along and take my foot off the throttle I feel a very slight jerky movement - very slight

Engine mount?

[tempragolf]

Thanks for the advice. I will have a go at this over the weekend. Thing is, my 2.0 petrol engine is an EW engine not XU. Is the stepper motor roughly in the same place? I'll have a search! Cheers guys

[tempragolf]

Well took the stepper motor off and cleaned it etc but no change! Back to the drawing board. Someone said that a buggered lambda sensor can cause these probs?????

[jasper5]

Yes, a faulty lambda can cause your symptoms, but so can other things.I replaced a faulty lambda recently on a Nissan Almera, similar symptoms as you have, but on the diagnostic machine, the lambda voltage read zero, the management light had been on and off for a couple of weeks previous.The fault code read as "fuel system lean".

Was the car ok before you fitted those 4 prong plugs? Some ignition systems don't like those plugs, they can alter the voltage and cause ECU faults.

Have you had a diagnostic check?

Change the fuel filter and fit some injection cleaner.

[mjb]

The fault code read as "fuel system lean".

Just to repeat something I've said 1001 times: The diag results are just what the ECU 'sees'

if the diag says 'lambda sensor error' chances are good your lambda sensor's correct, but it could be something BEFORE the engine buggering up that's causing odd lambda sensor values

Always treat diag codes as symptoms, not causes.

[DaiRees]

Always treat diag codes as symptoms, not causes.

That's a cracking bit of advice. Bet most DIYists treat fault codes are the word of God.

[jasper5]

I agree, but as a pro, a live data test is also done to trace the fault.....zero voltage from the sensor is pretty conclusive.

The fault code can list many possible causes, but live data is much more accurate.

On the Almera, for example, a fault code pointing to cam position sensor fault, more often than not, means that the timing chain is worn, you always have to remove the rocker cover and check the protrution of the tensioner....more than 10mm means a new chain and tensioner....the crank and cam sensors go out of phase and put the management light on.

It's all about experience!

[mjb]

That's a cracking bit of advice.

Not bad for a 2:30am drunken post eh? ;)

[tempragolf]

Well I changed the lambda sensor and things now work well again! Thanks to everyone for the great advice. Much appreciated.

[lakemaligne]

Hi ,your fault sounds very similar to mine.I have owned a MK1 1996 2Ltr LX petrol 406 from new.The car has covered 149,000 trouble free miles apart from a leaking A/C compressor. The problem I am having started over a year ago. For no apparant reason the engine tick over will suddenly remain at 1200rpm if i shift in to neutral while the car is still moving,and only drops to the normal 950 rpm once the car comes to a complete halt. This happens moving forward or backwards! The car will also jerk, as the power comes off when i completely lift of the accelerator ,instead of the usual smooth transition from engine driving the car to using the engine to gradually slow the car. When I depress the accellerator again,there is another jerk when the power comes back on. These symptoms will persist for a few days ,then clear itself for a few days, then come back again. The tick over instantly drops to normal once the car has stopped moving, which seems to suggest that a motion sensor of some type is involved with this fault. The dealer I originally bought the car from replaced the MAP and oxygen sensor to try and sort the problem, but that only caused the engine fault light to start appearing, which until this point had never appeared in the cars life. All the symptoms remained also. They then replaced the throttle pot and cable and reset the adaptives,but still the fault kept appearing.The fault is not linked to changes in driving conditions ,ie heavy rain or dry spells,or bumps in the road.The vehicle tech who worked on the fault said that the ECU had recorded an "intermittent fuel regulation fault"(MP511), but was getting a reading of Lamda1, and said that his laptop was showing emmisions of that of a new car,and every thing was spot on,but agreed with me about the car having the symptoms i described .I have since taken my car to another dealer ,as I had a falling out with the one I purchased the car from.This second dealer has also ran diagnostic tests and can only see the down loaded "Irregular fuel delivery" fault.They gave me some "Wurth-SeBesto" petrol additive to clean the injectors to see if that cured the problem,but it has not . Has any one any suggestions please. This is an annoying fault which makes driving my 406 very awkward at times,because she is usually a very smooth,quiet ,powerful car.
If any one reading this is interested ,i did fix the erratic speedometer fault my 406 developed a while back.

[tempragolf]

What was your speedo problem then? I have mine drop to zero now and then...

[lakemaligne]

The needle would not move until the car was doing about 10mph,then it would shoot up to 40 mph and stay there.It would then flick back down to indicate any speed it felt like displaying ,usually on the approach to a speed camera.I could get the gauge to behave for a while by banging the top of the dash just above the speedo ,which indicated to me that the fault was in the actual instrument pod itself.If this is similar to your fault ,I can explain what i did to fix it.

[ddoherty406]

Im having this problem with my 2l glx, please explain how you sorted the speedo! maybe make a how to if its not muh bother.