Cold hard start Rich erratic idle shenanigans

[scam75]

The plug on the loom to the AFM is a definite cause of rich running as the sensitivity of the signal wire to the ECU is degraded as it gathers resistance over time. That part of the loom, certainly on the turbo, also folds back on itself and can cause issues down the line. I solved a nightmare rich/very rich car eventually by spraying de-oxit on the AFM connector and as if by magic it was cured....and has been for 2/3 years now.

Stuart

 

[bmnelsc]

...

i also seem to remember that the fuel pump will not be switched on by the ECU until 200 rpm is reached at cranking

Hmmm - that would explain why my '91 has to crank a bit before starting rather than the near instantaneous startup of my other fuel injected cars. Thanks.

 

[924Srr27l]

...

i also seem to remember that the fuel pump will not be switched on by the ECU until 200 rpm is reached at cranking

Hmmm - that would explain why my '91 has to crank a bit before starting rather than the near instantaneous startup of my other fuel injected cars. Thanks.

All 8 Porsche big (4 cylinder) car's I've owned have done that ! Turned over slower and longer than virtually any other Vehicle!

although 200RPM will be achieved within milliseconds.....

 

[peanut]

All 8 Porsche big (4 cylinder) car's I've owned have done that ! Turned over slower and longer than virtually any other Vehicle!

although 200RPM will be achieved within milliseconds.....

I read that a lot on the various Porsche forums and two of my past cars a 944 Lux 85.5 and a 89 944S2 both had slow turnovers. However my current 944S2 89 spins the engine over like a terrier with a rat . I refurbished my starter and solenoid cleaned all the earthing points throughout including the starter solenoid and stripped out the alarm and immobiliser wiring which transformed the cranking speed. My car usually starts after only 2-3 revolutions and within 1/2 second .

I suspect that a lot of cars may have a fuel system leak issue which results in the system not holding any fuel pressure after shutdown and delaying engine firing.

 

[peanut]

Well there has been some development so i thought I'd add the outcome and current status to the thread.

I managed to start the car and get it to the garage last week and eventually got the emmisions right down to get an MOT pass however the rich idle mixture issue has not gone away or been cured yet so I'm still looking for the cause and a permanent solution. Heres what happened at the MOT station.

Quick recap car suffers with a rich idle mixture. It would hard start then on full throttle and pumping, then cold or hot the idle would hunt from 600rpm up to 1200rpm and back continuously until eventually it died from the plugs sooting up. The car revved normally and performed faultlessly with perfect throttle response up to WOT. At the testing station on the exhaust emmisions tester, I tried removing the connector for the ICV (idle control valve ) and within a few seconds the 02 and HC levels dropped significantly .With the ICV disconnected I believe the default condition of the valve is fully open as per cold start condition ? With the ICV disconnected I also removed one of the vacuum pipes and the 02 then immediately dropped from 10.031 right down to 1.783 ! within 8-10 seconds. (pass is 3.500) At the same time the HC also dropped from 1239 down to 138 ! (pass 1200 ) Incredible. So presumably the ECU had registered the extra air supply and adjusted the pulse rate to the injectors to lean the idle mixture back to normal .? Now I've just got to figure out why the engine is getting too much fuel at idle or insufficient air or whether the ECU is either faulty or not receiving the data from the AFM, ICV, or engine temperature sensor etc, New pump ,strainer and filter has now been fitted and the fuel pressure is stable at 3bar .Leak down test and flow rate are fine too so I'll start with cleaning and testing the injectors as the car has been stood unused for long periods over the past few years.

Following that I'll have to test all the sensor voltages in the ECU connector to make sure that the ECU is seeing what it should.

 

[scam75]

Have a go at cleaning up the connectors to the AFM like I said. It certainly won't do any harm. The signal wire (1-5v sensitivity I think) can cause havoc if it is not getting the right signal to the ECU.

Stuart

 

[Mike_Pollock]

Sounds like the ecu is fine. I would be looking at the AFM, can't see if you have cleaned / repositioned wiper in it, if so I'd go with Stuarts suggestion.

 

[George_Mayson]

Hi Mate,

I'm sure you saw my post a while back with a similar issue now solved. It's not exactly the same as yours and I know you will have tried most or all of this, but I wanted to do a very very quick recap and give some food for thought; (I was solving this for nearly 4 months)

[ul][*]Running Rich[*]Black Plugs[*]Poor idle - hunting around 600rpm[*]Perfect power/response at most throttle openings, but still rich at all throttles[*]Poor Economy[/ul]The things I tried that weren't the problem

[ul][*]AFM Tested perfect, including temp sensor[*]Coolant Temp Sensor perfect[*]Fuel Pressure at the rail perfect, including bleed down[*]Speed/Reference sensors perfect[*]ECU Plug contacts all good, and all readings at sensors duplicated at the Plug![*]No Oxygen sensor on my early '83 Car[/ul]What I found to be the fix

[ul][*]Found that moving the place the spring contacts the cogwheel in the AFM adjusts mixture - handily labeled for 0.1% CO increments. I made the AFM "Barn Door" harder to open thus changing the metering of the air to the computer, solving the rich running I had AT ALL RPM's and THROTTLE OPENINGS![*]Couldn't find anything else wrong with the system, so this fix is stable and no other component seems to be overworked[/ul]Hope this provides some food for thought, I also played about with thoughts of auxiliary air valves at idle but my Richness was AT ALL RPM's and Throttles! Simple fix was best rather than overthinking in my case

 

[Mike_Pollock]

That's very interesting George, I've never heard of any one doing that before, however I did try it on my 2.7 trying to fix what turned out to be a failed FPR......

 

[peanut]

Hi George thanks for posting .Yes I did see your fix I had been following your thread .

The more I read about these problems the more I believe it is something very simple and transitory rather than a component failure.

Adjusting your AFM has fooled your ECU into thinking the engine is receiving less air causing it to reduce the injector pulsing and weakening the mixture. It has clearly worked but I want to know why !.... Your fix is inventive but the problem is still there and we don't know what it is.The AFM didn't suddenly start giving false air flow data to the ECU .

I have pretty much followed the same troubleshooting tests that you have followed except I found a different fix by accident. Whilst my car was having emissions tested I noticed that the 02 and HC came right back down to normal when I removed both the vacuum pipe and disconnected the idle control valve connector.

This seems rather odd because with more air getting into the inlet presumably you would expect the ECU to register the increased air flow and actually enrich the fuel supply . Perhaps the increased air flow into the inlet is allowing the excess fuel to be burnt .

rain has stopped play for most of the past week but with good weather on the way I'm hoping to continue my testing tomorrow.

ps yesterday the car started almost normally on no throttle which was completely unexpected but an hour later it was back to hard starting on full throttle and pumping the pedal....?

 

[George_Mayson]

Depends whether the airflow through the idle control valve is metered? I'd say not - if you wanted more air to lean the mixture you wouldn't want it metered.

I agree it must be a simple fix - but what is it? Presumably the fault must be connected to what the vacuum pipe is attaching to, or to do with the idle controller?

IS your richness confined to idle or is it at all throttles?

 

[peanut]

I'll stick to this thread I think until this cold hard start and rich erratic idle issue is completely resolved.

Hopefully when it is resolved I can tidy up the thread and it will be a useful go-to resource for other owners when these issues effect their cars....and it will

So.....you know the old saying 1 step forward 2 steps back ?....well its pretty apt for my ongoing issues with this 944S2 this week.

Yesterday I removed the Idle Air Control Valve from the car and thoroughly cleaned it. its really easy to remove the IACV from beneath the inlet manifold. Don't whatever you do be tempted to remove the inlet manifold unless you have other work that requires the manifoldn to come off. Its 15 minutes work tops ! I'll attach a youtube video I made to show you how easy it is.

OPERATION

So ....it turns out that the 944S2 IAC valve is a revolving valve operated by a coil winding type solenoid housed in the body of the valve. Unlike the earlier 944 which have a 3x pin IAC, Later cars have a 2x pin connector.

The 2x pin IACV is fed a constant 12v+ and the valve is maintained in its normal default open position by a strong internal return spring. For normal warm running the IAC valve is kept closed against the spring pressure by the ECU which grounds the solenoid coil of the IACV .When the ignition is switched off the IAC valve loses its 12v+ supply and the powerful return spring opens the valve once again ready for the next cold start.

If the car is restarted some time later with a warm engine, the engine temperature sensor tells the ECU that the engine is not cold so it grounds the IAC valve ,...closing off the additional cold start air supply that normally bypasses the throttle for cold starting. Thats how I figure it works but I still don't really understand its operation fully

So its simple to see how critical the correct operation of the ETS and IAC are to cold starting the 944 engine.

On examination it looks like all the condensation this Winter together with the lack of use of the car had caused the internal surfaces of the valve to oxidize and expand slightly which effectively jammed the valve .A little carb cleaner and careful cleaning with bits of rag via the hose spigots soon cleaned it up fine and flashing the valve with a PP3 9v battery soon had it working smoothly again.

I was initially surprised that the 944S2 AIC valves default condition is open.... I had assumed that it would be the other way round but I suppose if the IAC valve were to jam or fail ,you'd want it to fail open so that the car could always start when cold. The rest of the journey the mixture would be rich but it would run and the ECU can compensate to some extent by adjusting the duration of the injector pulses every revolution of the engine.

Anyway I digress as the little man would say.

Today I reinstalled the IAC valve to test the cold start....absolutely no difference ! grrrrr

When I pulled the connector off the IAC valve during warm up, the engine promptly died !. I'm sure that that is diagnostic but I can't work out how right now...I need to eat and then i'll tell you all about another interesting development.

YOUTUBE VIDEO REMOVING THE IAC VALVE

https://youtu.be/yHAajWoRV6E