Strugeling to idle when hot

[s2_bo]

So my new engine is finished and its all fitted and running, but the idle is a bit odd.

I have two mafs to chose from, one in the stock position just after the airbox and one just after the intercooler.

If i use the stock maf the car will idle when its cold but once the engine warms up a bit it cant idle at all, if I push the clutch in any gear at any speed for more then a second or so the engine dies, the revs drop very quickly straight to 0

If i use the pressure mounted maf i dont get this problem but its not too pleasant to drive like this as its not been mapped yet and part throttle is a nightmare.
With the pressure mounted maf connected it idles but not to smooth, the revs bounce from 700 to 1300 quite regularly, this only happens once the car warms up.

If i have no maf connected the idle is fine regardless of engine temperature.

Both mafs are new,
All sensors are brand new too as is the RS2 turbo and the car is not showing any fault codes. Its still on stock 3b injectors and FPR atm till the remap.

Does anyone know if the RS2 turbo could be the course for this? Or has anyone got any ideas what could be coursing the bad idle when the vacuum mounted MAF is plugged in?

Im not to worried as its getting remapped soon ish but i am qurius as to what could be course of this.

Thanks.
Bo

[S2central.net]

Slowly here... you have rebuilt the engine and have RS2 turbo fitted - is that all - anything else ?

SUggest you try output tests to make sure the ISV is being tickled by the ECU.

Have you setup the throttle switch properly for when it clicks to idle mode ?

Check all the temperature sensors are fitted OK and working.

I'd stay away from pressure side MAF for now - mapping will be skewed off as you discovered.

[s2_bo]

Yeah there are a few other bits like full wagner kit, scat rods, rs2 shells, engine balanced etc etc.

I have tried 3 ISV's 2 of them were old and the one fitted now is new, the idle changes when its unplugged so i presume its connected up right.
Could you give me quick how too on output tests?

TPS clicks as soon as throttle moves and clicks again when throttle closes so thats set up ok. I have not checked all the sensors over yet, however they are all new apart from the lower rad temp sensor.
Which ones could effect idle?
Also there is no ecu codes coming up when everything is plugged in.

Cheers.
Bo

[S2central.net]

To activate the Output Tests, you must first connect the Jumper Wire across the Fault Code Connectors as shown in the above diagram and THEN turn on the ignition to begin the output tests.

DON'T START THE ENGINE. Remove the jumper wire after at least 4 seconds.

NOTE: The LED should also be connected so you can see the output test codes blink out, but it does not "have" to be connected to initiate the Output tests.

FUEL INJECTOR TESTS: After removing the jumper wire, code 4411 will be blinked out by the LED, indicating injector #1 will be ready for testing, open the engine hood, place your fingers down on fuel injector #1 and then open and close the throttle with your other hand. #1 Injector should click 5 times and then be quiet, place your fingers on Injector #2 and again open and close the throttle, Injector #2 should click 5 times, place your fingers on Injector #4 and open and close the throttle, Injector #4 should click 5 times, repeat for Injectors #5, then #3, after doing the last injector test on #3 the Output test will switch to testing the IDLE STABILIZER VALVE (ISV). You should hear this Idle Stabilizer Valve clunk open and closed. If you go back inside the car, the LED should now be blinking 4431.

Connect the jumper wire again for 4 seconds to go to the next output test:
Carbon Canister Test Code 4343, will be displayed and the Carbon Canister valve at the back of the engine behind and below the cylinder head will be cycled on and off. You may want to place your hand around the carbon canister valve to feel it operate.

Connect the jumper wire again for 4 seconds
Waste Gate Frequency Valve TestCode 4442, Waste Gate Solenoid will be cycled on and off. This valve operation is pretty loud, so you should be able to hear it operate.

Connect the jumper wire again for 4 seconds.
(Test #7) Code 0000, End of Output Test Procedure, fault code memory has been cleared.

NOTE: To repeat the Output tests, the ignition should be turned off for at least 20 seconds.
If Output tests are repeated, the INJECTORS will NOT be cycled again, unless the engine is started and run briefly.

[S2central.net]

You have a lot of new variables there Bo, but individually they shouldn't have any impact on idling... Obviously the new bearings won't be run in yet, but nothing should be that tight as to bring so much extra at idle as to make it stall.

Is the throttle body itself positioned correctly - there's the 5mm drill trick from memory to setup the gap at idle. Maybe it wants more air than the ISV can provide.

What about crankcase pressure - are you venting OK ? Just wondering if you plumbed that all back up OK - and what pistons rings used - something a bit odd / silly if it doesn't like to warm idle - thats what got me thinking about clearances when hot. Did you plastiguage all the new bearings for clearance ?

[twoqu]

The TPS might click but is it going closed circuit at idle? If you remove the rubber from the conector of the TPS you should be able to back probe the connections. Pins 4 and 6 are the idle switch ones with 1 being upermost. So its closed circuit at idle, open the rest of the time. If you don't have a multimeter you can just bridge those connections with a short piece of wire to see if matters improve.

[90/90qs]

A faulty coolant temp sensor would cause rich mixture after the engine warms up and cause the symptoms you describe.

[s2_bo]

You have a lot of new variables there Bo, but individually they shouldn't have any impact on idling... Obviously the new bearings won't be run in yet, but nothing should be that tight as to bring so much extra at idle as to make it stall.

Is the throttle body itself positioned correctly - there's the 5mm drill trick from memory to setup the gap at idle. Maybe it wants more air than the ISV can provide.

What about crankcase pressure - are you venting OK ? Just wondering if you plumbed that all back up OK - and what pistons rings used - something a bit odd / silly if it doesn't like to warm idle - thats what got me thinking about clearances when hot. Did you plastiguage all the new bearings for clearance ?

Thanks for the info,
Can someone shed some light on the 5mm drill trick? I didnt know that the TB had to be set up. As far as im aware it closes fully when the throttle is shut off. Maybe im starving it of air.

I have a catch tank that is venting all the crank pressure, its all cleaned so there shouldnt be any restrictions there.

I used new OEM piston rings and they were instaled to sepcefications too. I checked the crank with a plastigauge and it was well within spec.

I also compression tested the engine, before i ran it in The dry test showed difrences of up to 1 bar but the wet test showed that all cyliners held practicaly identical pressure.


Im still wondering though why this dosent happen when the pressure mounted MAF or no maf at all is plugged in.

Thanks for your input guys,

[Jamo]

Posted in your other thread, this has been seen before and was to do with false MAF readings on vacuum side, only moving to pressure side cured it.

Never heard of it with a RS2 turbo though

[S2central.net]

I'll try to remember to lookup the TB setup with 5mm drill... Also thinking about air or PCV leaks and the possibility of unmetered air.

Have you tried both MAFs in both positions yet ?

With VAGCOM you can see the LOAD value coming from MAF - it would be nice to know if they are same at idle with both MAFs in both positions.

3B - Group 0 - Field 2

[Jas11n]

[Rusty]

Could be that you have a leak on the maf to turbo hose or boost system. That would explain the differences in the two maf positions. If it's not calibrated then that may explain why it idles but not steady, it could be out of range. Boost leak test the whole system from the maf hole if you've not done so already. HTH

[s2_bo]

Cheers guys. I will check all these things today.

Will let you know what I find.

[s2_bo]

Ok i spent a couple of hours checking things over today.

All the sensors are properly connected and wired up, the TBV potentiometer is correctly set up, there are no boost leaks.
The PCV is fully removed apart from the valve which is still connected just to keep the ECU happy, its venting to atmosphere and when you remove the sump vent pipe while the engine is on there is plenty of gasses flowing out so its not blocked or restricted.

I checked the TBS with a multimeter, its reading 0 at idle and around 10v when the throttle opens.

Its not managing to idle at all when the engine is warm now, revs bounce from 600 to 1000 and then after about 20 seconds it dies.

The weird thing is that as soon as the vacuume maf is unplugged its all fine. Idle stays dead on 900, when you blip the throtle it picks up and when you let off it drops back down quite quickly to 1100 and then dampens to 900 again.

If thinking Jamo may well be right and the vaccume mounted maf is getting incorrect readings coursing it to stutter and then die.
I have tried both mafs in both locations but have not measured outputs yet as i have no access to vagcom atm.

All very strange ...

[jameswkr]

The "5mm drill bit" adjustment is for the throttle damper ....basic throttle setting is full shut then approx 1/4 to 1/2 turn in on the stop screw and lock ( before setting the damper ).