Okay, so I own a 16-valver for about a year now. When I got the car it was idling fine, but after a few days after releasing the throttle it would do the common problem of idling hunting from 1300-2000 rpm. Disconected the battery terminals several times, until one time It started normally and was hunting from 1000-1100rpm. After a few miles I noticed that when I stopped completely it would idle at 900rpm. And that was it, within a matter of days the hunting was completely gone and the car would always idle perfectly.

 

Fast forward a few months and the problem started again, but much much worse. It would do the usual of not idling correctly but would not fix itshelf by just disconecting the battery.

I started digging and to date I have done the following.

Changed the distributor,

changed the temp sender,

cleaned throttle body,

blanked off the egr,

replaced all the vacuum hoses,

changed spark plugs,

tried a different throttle body, (Mine is 036133064E and the replacement was 036133064J)

changed the MAP sensor, (although I am not sure if i got the correct one),

Checked for continuity between different sensors and the ecu plug. Results are: Temp sender: Three out of four wires have continuity to the ecu pins The fourth one i pressume goes to the dash(?). MAP sensor: All of the wires have continuity to the ECU, however one wire has continuity to 2 different pins of the ecu, could not find continuity beetween the sensor's pins and ground. Also when the ignition is on the 2 middle wires have +5v

 

After all this, the car is still hunting, but less, (1300-1400rpm) and when I stop completely it idles at 1100rpm and not hunting.

BUT after all this the car is no longer running as it was. It has doubled in fuel consumption and the plugs come out dark indicating it is running rich. Also there a noticable power loss overal, but the most frustrating thing is that off the line the car is chocking even at full throttle until i pass the 2000rpm mark.

 

Vag com ruturns ABS faults (Bad ABS module) and throttle position sensor error but this can be attributed to running the car without the TPS plug for testing.

 

I tried running the car without the o2 sensor, nothing changes. Today as i was messing arround i unpluged the TPS plug and the MAP plug. The car was idling perfectly, but as soon as i opened the throttle it would choke and die since it has no idea how much air is going in.

 

I believe the problem can be traced to bad wiring or bad TPS sensor in the throttle body.

 

What should I try next? Does the wiring sound right to you? Any ideas are more than welcome. 

 

Was it a genuine VAG blue temp sender?

 

Wires need bad treatment to break. Connections can become poor and just need cleaning of oxidation.

 

As you have replaced so much I'll guess the plastic brake servo tube has a tiny split, and is letting in excess air down stream of the throttle plate, so the MAP sensor reading is way off at low speeds when there should be vacuum. 

 

Or the Exhaust Gas Recirclution valve is crudded or leaking.

 

 

 

 

Did you do throttle body alignment when changed TB?

 

Hi, thanks for the reply,

 

The temp sender that was in my car was an original. The replacement was not. Both are working okay though confirmed through checking real time temp on vcds. I have changed between the 2 senders multiple times. Nothing changes, both are working ok. Also both senders have the yellow ring not the blue one.

 

The EGR is blanked off, and the little egr valve controller solenoid is unplugged, so even with the valve stuck open no exhaust gas can enter the manifold.

 

Finaly the brake servo hose has been replaced as it indeed had a split resulting in the brake losing assistance quickly when the engine was off. Now it is fine.

 

I have tried to align the TB on VCDS but I have not been successful. It won't let me. I do not own a copy of VCDS so i have to visit the local garage to do it. Then again how can the TB lose aligment from one day to another with no changes to the car at all. The problem started out of nowhere.

 

Today I noticed the EVAP valve is constantly clicking. This means it is open right? 

Edited 24 April, 20224 yr by contactnfsu

Update:

 

Today I tested the TB Wiring. I found the black/red wire to be power, the brown/white wire to be the ground.

Then the blue/red wire appears to be the signal of the tb plate to the ecu. When ignition is on it has 5v or very close to this. When engine is on it receives 4.3v and as you open the throttle the voltage drops.

The yellow/white wire appears to have something to do with idle. When the tb plate is closed it has 0v and when the plate moves slightly it jumps in voltage to 4v approximately.

 

That's all i figured out. My plug is an 8 pin but has 7 wires going into it. So that leaves 3 wires that I have no idea what they do. 

 

Also my MAP sensor is an NTK 92899. Does someone know if it is correct for an AFH engine?

Also the red/black wire which is apparently power to the throttle body has 12v at the ecu plug and 5v to the throttle body plug, how can that be?

Really same wire?

 

Alignment - ECUs learn from O2 sensor feedback and correct the base map with a fine trim, so it's a moving target. Changes of ambient pressure also affect air density.

 

An EVAP purge valve leak will give symptoms similar to what you describe

https://www.yourmechanic.com/article/symptoms-of-a-bad-or-failing-canister-purge-solenoid

 

Not come across one clicking before... but sounds plausible. I'd expect it to only open when engine warm for short  period. Plug the hose from Carbon canister and see if that helps idle?

 

No Exhaust Gas Recirculation will mean more oxygen is present than ECU commands, so it'll burn lean, then over- compensate when O2 sensor detects that condition before the cat, and emissions and consumption will be poor.

 

Thanks for the reply again! 
the car was doing all of those symptoms even with the egr on. I will reconnect it to the car for testing, however I have somewhat forgotten how the vacuum lines should go from the manifold to the egr controller as I have removed that too in case it was leaking and then blocked the vacuum lines. If someone has a pic of the vacuum lines at the egr controller I would appreciate it. I am in the garage right now and just tried to block the vacuum line from the evap canister. Still nothing.

 

As for the wire I did a continuity test and indeed confirmed it’s the same wire. Red black on the ecu and red black on the tb plug. On the ecu it has 12v and at the plug 5v.

I don't have a Throttle body engined car to compare voltages.

That says there's a big resistance in the wire or contact, or the act of using multimeter is interfering with the system being measured.

 

Vacuum lines plumbing. I wonder if Haynes or Autodata have a diagram... or find a photo of an engine bay? Sorry not v helpful, I know.

 

I think you can more successfully remove the evap carbon canister system than an EGR. Might be worth fitting a vacuum gauge and seeing what idle vacuum below throttle plate reads, or if it varies a lot when stationary. 

 

Burnt or sticky valves can play havoc too.

 

Checking voltage supply and wiring to control unit

‒ Remove air cleaner => Page 24-20, Fig. 3.

‒ → Detach connector -1- from throttle valve control part -2-.

‒ Connect multimeter to measure voltage at connector contacts 4+7.

‒ Switch on ignition.
Specification: min. 4.5 V

‒ Switch off ignition

‒ Connect multimeter to measure voltage at connector contacts 3+7.

‒ Switch on ignition.
Specification: min. 9 V

‒ Switch off ignition

 

Check wiring between throttle body and ECU connector for open circuit according to current flow diagram.
Contact 1+socket 2
Contact 2+socket 26
Contact 3+socket 10
Contact 4+socket 14
Contact 5+socket 41
Contact 7+socket 17
Contact 8+socket 16

 

For some reason pin 7 isn't shown in the diagram below, but it is connected to the throttle closed switch opposite pin 3 and is ground wire 

 

 

 

Thanks for the useful information nige!

 

I did measure voltages as described. 
Everything checks out okay. Contacts 4+7 measure at 5v and 3+7 at 10v. These voltages are with the plug out of the tb socket. 
 

I did the measurements with the throttle body plug on the tb and contact 3+7 has no voltage. It gets voltage when you open the Tb plate. I suppose this is normal?

 

I also did the continuity check between the throttle body plug and the ecu connector. Everything checks out as described above, except for pin 7 on the throttle body plug, which is the ground, and also has continuity (except socket 17 on the ecu plug) to other sockets in the ecu plug. But I suppose this is normal as it’s the ground cable. 
 

The search continues. I also rewired the egr valve for testing. No difference. 
 

At this point I think I have to perform a compression test to rule out a mechanical problem in the motor, like burnt valves as described above by dvderlm.
 

I have no idea what other Sensor to check. The o2 sensor maybe? 
 

 

1 hour ago, contactnfsu said:

Thanks for the useful information nige!

 

I did measure voltages as described. 
Everything checks out okay. Contacts 4+7 measure at 5v and 3+7 at 10v. These voltages are with the plug out of the tb socket. 
 

I did the measurements with the throttle body plug on the tb and contact 3+7 has no voltage. It gets voltage when you open the Tb plate. I suppose this is normal?

 

I also did the continuity check between the throttle body plug and the ecu connector. Everything checks out as described above, except for pin 7 on the throttle body plug, which is the ground, and also has continuity (except socket 17 on the ecu plug) to other sockets in the ecu plug. But I suppose this is normal as it’s the ground cable. 
 

 

I would not expect any voltage across 3 & 7 when it is connected to the TB as that is how the ECU confirms the throttle butterfly plate is in the closed position, which you confirmed when you opened the throttle butterfly plate.

 

With the continuity from pin 7 to other pins on the ECU is to be expected as it provides a ground to the MAP/IAT sensor (pins 43 & 37) Coolant temp sensor (pin 42) & Disributor sensor (pins 8 & 13)

 

What year is the car ? 

 

When you replaced the Coolant temp sensor was it a genuine VW part or one from a non branded parts outlet ? as non genuine ones can lead to all sorts of problems.

 

You can normally get around the throttle body adaption by just driving for around 20 mins with the coolant at a "normal" range using varying throttle loads. Also you said before it would not do the TBA with VCDS if the ECU is not seeing the coolant temperature of at least 80c it will not run the test, which brings me back to my previous paragraph about non genuine sensors

Wow, thanks again for the quick reply. 
My car is 1998 or very late 97. The registration says 1998, but many parts have 1997 stamped on them. So can’t really be sure. I am really determined to solve this issue, I love my little valver.
 

The replacement temp sender is NOT a genuine one. However my previous temp sender which came with the car when I got it was an original. Both senders appear to show temp in the dash okay. Maybe the original one is bad, and the not original replacement isn’t working as it should? Possible.
 

Is there any way to test the sender to see if it’s working properly (the original one)?

 

I have also done a continuity test previously between the temp sender plug and the ecu socket. I find continuity on three out of four wires. The fourth one I suppose goes to the dash?
 

lastly my car has another temp sensor, (2pin) as it’s equipped with AC.  (I have read it’s to cut the ac if the car gets too hot) Does this sensor play any role in the ecu information of temperature? 
 

 

The coolant temp sensor is a dual element device with one for the ECU the other does the dash display, so it's quite possible for the dash to be reading correct, or within it's strange design feature that the gauge will show 90c for an actual coolant temp of between 75 ~ 107c ? and the other half of the sensor is sending false info to the ECU

 

You could try this resistance test, so at 80c your looking for about 340 ohms 

 

That additional sensor on the thermostat housing for the AC is just a thermal switch to stop the AC if the coolant gets too hot and it only signals the radiator fan control module and that does send a signal too the ECU so the ECU can adapt for the loading that the AC compressor will cause but the switch is only used when the AC is switched ON

 

The 4 pins on the coolant temp sensor

Pin 1 Brown/White wire signal ground back to ECU Pin 17

Pin 2 Brown/White wire signal ground probably again back to ECU Pin 17?

Pin 3 Blue/Green wire ECU temp signal pin 42

Pin 4 Yellow/Red wire Dash temp signal 

Thanks for all your help nige! 
 

Update: Continuity tested the wires as mentioned above. All is good there.

 

Then I proceeded to do the resistance test. I a complete noob on electrical. I put the multimeter on ohms. One probe went to battery ground and the other to the blue wire which is temp signal to the ecu. If I have done something wrong please correct me.

 

Fully warmed engine, and the resistance was 220-240ohms. Not 340 as nige mentioned. 240ohms means the ecu sees the engine overheating?  
 

 

That was the correct way of testing,  240 ohms would indicate the ECU is thinking the coolant is 85~95c so not too far off normal, I would re-do the same test with the engine at ambient temperature so leave it overnight and check it in the morning

Update: 

 

Temp sensor seems to be okay. With the car cold it reads 1200ohms and when fully warmed 200-240ohms.

 

I cleared all the codes off the ecu today (playing arround with the sensors and disconecting plugs had introduced some faults) and took a trip. After a 500km drive I checked again, no faults re appeared.

 

After the drive I noticed 3 things:

 

1. Turning the ac on nearly vanishes the problem. It still idles high at 1000-1100 rpm but it does not idle hunt. The same happens when I turn the wheel at full lock. It seems that when you put a load on the motor it fixes itshelf.

Together with what nige said above about the ac system it got me wondering... Maybe the ecu gets info that the ac is running and conpansates for the load, while in reality the ac is off resulting in the idle hunt situation. As soon as the AC actually comes on the engine smooths out. Probably I am talking nonsense, it's just a thought.

 

2. I always had a small exhaust leak, not noticable at all. Today I noticed that the leak must have gotten bigger as I could hear the exhaust leaking and rattling from down my feet at certain rpm. Could an exhaust leak produce an idle problem? I'll go get it patched up tommorow.

 

3. My ac has developed a problem. It was working fine until now but today I turned it on, and no cold air inside.  The ac line going to the evaporator gets cold, and then freezes (with actual ice covering it) if you leave the ac running for a long time, but the evaporator does not get cold. The compressor is working, the refrigerant level is good, I checked. Is there a valve that connects the evaporator to the ac lines? It seems like it's a valve is stuck not allowing the cold to reach the evaporator.

Those resistance figures look good so looks like we can rule that out of the problem.

 

You could unplug the radiator fan control unit (under battery tray) that will eliminate the AC ON signal to the ECU

 

Something else to try, connect a jump cable from the to the engine just to rule out a poor earthing problem

Sorry, you mean a cable from the battery negative to the engine nige? 

Yeah sorry missed to the battery neg,

 

On the AEX there was ground point near the inlet manifold for the sensor but I can't recall if there is similar on the AFH, if not somewhere like the distributor mounting bolts ? 

Update:

 

Removed one plug from the fan controller. (small one). No results. Still the same issue. 

 

Connected a thick cable from battery negative to engine. (At the head, could not find a good bolt to do a solid connection on the block). Still nothing.

 

The investigation continues.

 

I have been noticing that when the engine is cold, the issue is much less present. As the car warms up it becomes progressively worse. 

Also if I remove the oil fill cap, there a smell of gas in the oil.

 

I want to know more about the pcv system (black box behing the engine), but cant get any good info online, Anyone know how it works?

Does it get vacuum from the engine?

The PCV system

#28 connects to #3 below

 

This is the inlet vacuum system, not showing is the vacuum pipe to the fuel pressure regulator that you can see in the above picture,  

Nige you are a legend!

 

I am out for the weekend so I'll post the updates on Monday when I'm in the garage.

 

Based on the the pics above I'll check if there is a vacuum leak where the egr pipe meets the intake manifold, and I'll remove and clean the pcv canister.

 

Again thank you for everything!

Update:

 

Removed the pcv caninster/oil seperator. One port was completely blocked and in general it was filthy. I washed it with gasoline. I couldn't wrap my head arround the ammount of gunk that was in there. 

Anyway, now it's clean as new. I suggest everyone does this on their 6n once in a while.

 

Good news is that now the smell of petrol in oil seems to have gone away.

Bad news is that the idle issue is not fixed.

 

After everything the car seems to behave better. Now it starts perfectly everytime and does not idle hunt. The hunting appears only when the car warms up and only if I press the gas pedal to the floor once.

Any suggestions are welcome for what to try next. I think I am running out of ideas.

 

Could it be a bad tps? A bad ecu? Any ways of testing the tps?

Can't find any definite resistance checks you can do on the TPS only to see in live data that it goes from 0~100% smoothly