96 Polo 1600 Idle Problem

[ironmaiden67]

:mad::mad::mad:Hi,I have a 1600 Polo that has got bad idling problems,despite checking and changing all the obvious.The computer showed up a problem with the Throttle Body so it was changed for a new one,but after warm up it promptly reverted to it's previous state,which was uneven idling (700-1400 rpm) before stalling.The engine will start up and run,but has a distinct flatspot,which is almost like fuel starvation.The idle will stay like this until the engine has cooled down.It will then run ok and idle at app 850 rpm until the temperature gauge reaches normal and the same thing happens again.The computer test shows no other faults other than the Throttle Body and just about everything else has either been changed or checked.
The temperature sensor has not been changed as the reading is showing 85 degrees when tested on the computer.The Throttle Body was a new one and not a "reconditioned unit"as some are advertised.Any ideas would be most welcomed,as I have run out of ideas....Thanks.

[g40jon]

dizzy timing could be out a bit. it can cause a lumpy idle. was the new t/body reset when fitted?

[Crasher]

I agree with Jon, the throttle body was probably not reset.

[ironmaiden67]

dizzy timing could be out a bit. it can cause a lumpy idle. was the new t/body reset when fitted?

Thanks for the reply.With regard to the reset of the throttle body it was supposedly reset by a local garage after I fitted it.The problem there was the man only had a crypton analyser and did not seem to know what I was talking about when I mentioned VAG COM.He insisted his computer was able to reset the body,but I had my doubts.I think you are probally right and I am getting it reset by a Bosch guy that has the right equipment.Funny thing was the other guy said he has never had a problem with the reset on these throttle bodies with his crypton equipment.It was him that originally diagnosed the faulty throttle body.Anyway I will let you know the outcome once the Bosch man has checked it out............Keith

[ironmaiden67]

:mad::mad::mad:Well it looks like this is going to be an ongoing thing,as the engine still refuses to idle even after the ECU was reset properly.The Bosch computer shows no faults and he has reset it a total of three times,but each time it reverts back to it's former state.He disconnected the MAP sensor and the engine still ran and actually made an improvement.He said there was no way the engine should run with this sensor inoperative.He is now of the opinion that the ECU is corrupted and said he might be able to get it reprogrammed.He also said if the car has not got the factory fitted immobiliser,which goes through the ECU,then I might be able to fit a secondhand one.Any advice on the above would be most welcome,as the car is really beginning to bug me.

[Crasher]

ECU failure is extremely rare; having an idle problem without a fault code is odd. I am not familiar with the Bosch KTS idle reset procedure but in VAG speak it is in Basic settings 04, display group 001. Is he doing this with the engine running or the ignition on and not running?

[ironmaiden67]

ECU failure is extremely rare; having an idle problem without a fault code is odd. I am not familiar with the Bosch KTS idle reset procedure but in VAG speak it is in Basic settings 04, display group 001. Is he doing this with the engine running or the ignition on and not running?

Hello mate,He did the reset with the ignition on ,but with the engine not running.The other garage did it with the engine running,which I thought was wrong,but who am I to tell him his job.As the Bosch computer was doing the reset you could see the throttle body opening to different settings and then closing.All the settings were spot on,including voltages.The geezer was ripping his hair out (what little he had) because there were no fault codes showing up and the car just would not run right.Until it warms up you would not know there was anything wrong with it.Maybe I should flog it while it is cold and take the money quick.

[Crasher]

He could try deleting the learnt values which in VAG speak is Adaptation 10, group 00 read and save but again, I have no idea what it is on the Bosch KTS.

[ironmaiden67]

He could try deleting the learnt values which in VAG speak is Adaptation 10, group 00 read and save but again, I have no idea what it is on the Bosch KTS.

I think this motor is sending me a little mad,as I am getting my MAF's mixed up with my MAP's.I will point out the values you have given and see if he can make anything of them.It has got to be a reset problem,as everyone I have spoken to is saying the same thing and like I said before there is nothing left to try.Whether the ECU firmware is somehow corrupted and wont save the data that is input is something that I am also being forced to consider.It might be possible to flash the eeprom if the firmware is available,which I doubt it is.Thanks for the help,I will let you know if I get it sorted.

[Crasher]

Your car doesn’t have a MAF sensor, only a MAP (Thrust) sensor.

I had one of these the other day that was driving me nuts like this, it turned out to be a tiny and impossible to see or hear split in the plastic inlet manifold. We fitted a new manifold and it cured it. That gave an idle adaptation fault code though which yours isn't doing.

[ironmaiden67]

Your car doesn’t have a MAF sensor, only a MAP (Thrust) sensor.

I had one of these the other day that was driving me nuts like this, it turned out to be a tiny and impossible to see or hear split in the plastic inlet manifold. We fitted a new manifold and it cured it. That gave an idle adaptation fault code though which yours isn't doing.

Thanks for that mate.I will have a good look around the manifold,etc.I originally said MAF sensor,but edited the post to MAP sensor when I read through it.Like I said this motor is driving me to distraction and I will most likely end up in the local loonie bin if this goes on much longer.

[Crasher]

I tried to pick up the leak on the one I was doing using commercial leak detector spray and could not find it, even though I knew it was there. The only way I could prove my theory was to get the customer to change the manifold (I was diagnosing the fault for another garage) and changing the manifold solved the problem. Incidentally, that one ran better with the MAP disconnected and after it was done, I found the ignition timing was also out. I had suspected the timing of being out but with a fault code stored you cannot initiate Basic Settings group 001 with the engine running and this is the mode in which you check the timing.

[ironmaiden67]

Crasher,the MAP sensor has been changed and did not make the slightest difference.He also used leak detector and could not find anything.All vacum hoses have been rechecked and no fault has been found.He has eliminated the coil and distributor and is of the opinion that it is not electrical.He deliberately induced a fault on the TB and it showed up on diagnostics as 3 faults.He then rectified the induced fault and reset the TB and all was clear with a reading of 0 faults,but the engine is still running exactly the same,i.e,idle varying between 850-1400rpm,then dropping to nothing and stalling.Restarting the engine will temporary clear the problem for app 30-60 seconds and then it starts all over again.
The engine still runs perfectly ok whilst it is warming up,but as soon as the temp gauge hits normal the fault appears.He has obviously eliminated the temp sensor.There are no leaks around the servo or adjoining hoses.I was wondering if it might be possible to change the ECU for a secondhand one to see if there is any change.According to the Bosch man the immobiliser is an aftermarket fitting and does not route through the ECU,as he thinks the car is to early.Could you confirm that this is the case with a 1996 Polo,as this will obviously make a difference.I think what you are saying about the Manifold is looking very possible,but it is the lack of fault codes that is strange.The other possibility that has crossed my mind is contaminated fuel,maybe water,but the fact that the car is running nigh on perfect at driving speeds tends to eliminate that little theory.The tank was filled up with fresh petrol before this started.I really don't know where to look next.

[Crasher]

If your car has a key fob or plug immobiliser, that is aftermarket and nothing to do with the ECU, BUT your car definitely has a factory fitted passive immobiliser with a chip in the key and the immobiliser box, just under the dash next to the steering column, is coded into the ECU. Swapping over to another ECU of a suitable number is easy to do; the ECU and immobiliser can be readapted to each other in seconds. PM me the cars reg and your email address and I will send you some info.