MK3 Golf stuttering under load at 3000rpm

[aris]

Apologies for the re-post - I posted this in the Passat forum after I found my symptoms with a google search.

I have a problem on an 8v MK3 GOLF GTI (1997):

Car feels a bit flat, but when I get to about 3000 RPM, the car stutters quite badly. If I lay off the accelerator and accelerate gently then it is a bit better. It is also a fair bit better if I put the accelerator down to the floor when accelerating. The problem only happens under load - like on the motorway. I'm stationary with the clutch disengaged, then the problem does not occur.

I tried replacing the ECU relay (the one marked 30) - this did not help.

I took it into the garage, and the diags said the lambda was out - so we replaced this - along with the rotor arm, cap (they were looking a bit cracked - they needed replacing anyhow), and also a temperature sensor.

No joy - same problem.

The ECU relay I replaced the #30 one with is not a VW one - but an aftermarket one - could this be making the difference? Changing this relay really did make no difference.

I've had this problem for over a year - and intially I changed the plugs and leads, and air-filter. No joy there either.

I don't want to go putting good money after bad and changing everything in sight.

Any ideas?

Thanks,

Aris

[aris]

The lambda was installed yesterday, and it does still stutter, but the car does feel smoother and more responsive when it is not stuttering. I've not checked for any codes since the new lambda has been put in - will do that this week perhaps.

[Crasher]

Normally a lambda sensor fault code is more symptomatic rather than being the problem itself, huge numbers of lambda sensors are replaced for no reason and often a new senor will be ruined by installing it into a faulty car. I have lost count of the number of sensors I have had to replace that were already new after I have cured the fault as the previous garage had done what I call “barking at the code” and just replaced the senor as it came up as an error. I image a code read will bring up the same code so when you have the results, please post them.

[aris]

OK - no more codes on the diagnostics machine. Some progress though - after some fiddling about he decided to disconnect the cable from the Air Mass Meter - and after that the car is running like a dream. No misfires, and it goes like it has just had a coffee enema. Logically I would think that the Air mass Meter needs replacing - or can it be fixed, or cleaned, or could it be something else wrong that disconnecting the Air Mass Meter would affect? Thanks,

[Crasher]

AMM's cannot be cleaned or repaired, only replaced. Only buy a new AMM from a VW dealer under the part number 037 906 461 BX, aftermarket (typically from fleaBay) supplied AMM's have been causing terrible problems and from VW they are only £96.35.

[aris]

Thanks for the info. Are the ones from German and Swedish ok? Their website says they are Siemens. Is there a problem in running with this disconnected? It has been 100% without it. Will I see poor fuel consumption perhaps?

[Crasher]

If I had meant the ones from GSF were OK I would have said so but at least it is better than fleaBay as long as they are genuine Siemens and not a reconditioned Siemens unit in a white box. I have to say I am having terrible problems on a daily basis with parts that I buy from both GSF and ECP, we have to be very careful what we buy from both of them. I only but AMM's from VAG. It isn't acceptable to run the car with the MAF disconnected as the fuelling will be wrong which will eventually cause a lambda error and possibly shut down the catalyst and cause increased emissions. If it was OK to run it without one, VW wouldn't have bothered fitting one in the first place. Once a new AMM has been fitted, you will need to have the fault code erased that will have been stored due to it being disconnected. It is also distinctly possible that fitting a new AMM will bring all the problems back and so that in the end, that the AMM wasn’t faulty.

[aris]

Oh dear - a 100 quid part, replaced and it still might cause the original problem? Is there any way of testing the mass meter on the bench? What else could I look at before replacing this expensive part?

[Crasher]

That is a good question. It is near impossible to diagnose a faulty AMM, the only way I have found to be reasonably successful is "No codes, running problem, fit new AMM, keep fingers crossed" and it usually works but it isn't 100%. What I would say is that the unit used on the ADY/AGG (which is usually Hitachi if my memory is working) is very reliable (unlike the current Bosch items) and I have only replaced a handful over the years and some of those turned out to be a mistake.

[aris]

I'm fairly certain mine is an AGG (how can I confirm this?) - according to the GSF website AFT/ADY/AGG is a Siemens part which they sell. Reliable enough?

Aris

[Crasher]

I can tell if you PM me the reg or chassis number and the brand of AMM is moulded into the AMM.

[aris]

I had a look at it - it is a Hitachi. If I went to VW and bought one, do you think it would be a Hitachi?

Aris

[Crasher]

I would expect so.

[mjpuds]

What damage can be done by spraying a carb cleaner or something like this into the AMM...

[Crasher]

The thin film transitor can have debris washed onto it and besides, this post is over 11 years old...

[mjpuds]

So is my car.. in fact it is feeling about;) 95..