[dry664]

My car is doing a couple of things it shouldn't. Firstly the throttle is lumpy when cold and secondly the engine tries to stall when taking foot off the accelerator when cold (revs drop, especially when the air temp is cold). Its always had the lumpy throttle when cold, it started doing the stalling thing after a top end rebuild so I think this is likely two separate issues.

I've checked a number of things including:

- Changed ICV for a used replacement

- Changed and tested DME Temp sensor

- Changed and tested <acronym title='throttle position sensor'>TPS</acronym>

- Tested hall sensor

- Passed a vac leak test



My mechanic had a look last week. Checked for faults using a Hammer (3rd time in 6 months) and nothing comes up. Ran the car with the Hammer attached. Car runs rich when cold with electronics trying to even the mixture. Runs perfectly when warm.



He's given me a few things to try and also invited me to cannibalize his ClubSport for parts to test parts. Any thoughts?

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[dry664]

Come on chaps I could really use some help with this!



I used the car for the first time in cold/damp air since last winter and it starts up really rich. When you let the revs drop it tries to stall. Once its warmed up it runs beautifully.



Any ideas??

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[dry664]

Other things I've done...

- Changed DME relay

- Cleaned <acronym title='mass air flow'>MAF</acronym>

- Checked oil cap seal ok

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[Bulti]

Is the throttle body clean and are it's seals ok?



A bad coolant temp sensor could also cause these symptoms, but you say it runs rich when cold...

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[94SilverCab]

Cap and rotor?

Spark plug wires?

Fuel Filter?



Lots of possibilities.



Don't cannibalize a Club Sport (Best advise in this post)



Jay

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[dry664]

Throttle body is clean. I assume its seals are ok as its passed a vac test.



Replaced the coolant temp sensor already, then tested the old one which was fine and replaced with that.



Are cap, rotor, spark plug wires or an old fuel filter likely to cause the car to run rich? I guess the only way to test these is to replace the lot?

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[Bulti]

It is supposed to run rich when cold...



Check the wires in the dark, you would see sparks when badly worn.



Cap and rotor could be checked easily when looking at the contacts, according to some here (who could know) they wear off quicker than one might think. They are quite cheap to replace if I'm not mistaken.



If the fuel filter is more than 2 years of age I would replace it.

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[flash]

it is only supposed to run rich for about 60 seconds. then it goes to stoich. i think there is actually a timer built in.



definitely check more closely for vacuum leaks. a small one, like at the ported throttle, the lines under the manifold, and such, will cause this symptom.



has the throttle body plate been incorrectly adjusted? if it is closed off, and the ICV isn't working properly (which could be electrical) you won't get enough air in there



check the seal at the oil filler cap. if it is leaking, you will have a vacuum leak





how old is the O2 sensor? those things are only good for about 60k miles



what chip is in there? are there any other mods?

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[dry664]

Bulti,

Some good stuff to check there. Fuel filter hasn't been changed since Ive had the car and no record of when it was last done before that. I have a brand new filter that's waiting to go on.



Flash,

I will have another look at vacuum leaks but Ive spent a good couple of hours tracing everything and my mechanic went round everything with some carb cleaner. I think the next thing would just be to replace all the hoses?



Can you elaborate on your comment on the throttle body plate? What adjustment? I know there's a small screw to adjust its starting position. Is that what you mean? What electrical issue could cause the ICV to work incorrectly?

Ive tried two ICV's now having tested both off the car and they both sounded like they were working correctly. Both show exactly the same stalling issue so unlikely to be the ICV?

Oil filler cap seal is ok.

O2 sensor is old but I believe the car doesn't start taking data from the o2 sensor until its warmed up? Ive run the car with the O2 unplugged, still has the stalling issue.



Car is running a ROW Promax chip on 98 octane fuel. I only installed the Promax a couple of weeks ago (after my original post) to see if it would sort the issues out. Its 99% eradicated the lumpiness but the stalling issue remains. Only other mod is airbox per your spec. Once its warmed up it pulls like a train.

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[flash]

carb cleaner is no way to test for small vacuum leaks. you won't find anything that way. that's fine for an intake manifold and stuff like that, but there are too many ports on this car for that to work. you have to pressurize the system and look at a gauge.



there is a test in the durametric for the ICV, but basically the ICV opens and closes based on a signal it gets from the ECU via the connector that plugs into the ICV. if it isn't opening, it won't run right.



the car takes data from the O2 sensor almost immediately. "warmup" is only 60 seconds. you can just about set your watch by it. that being said, if the issue persists with the sensor disconnected, then it seems all the more likely that it is the sensor. however, if you are saying that the symptom goes away when it is warm, whether the sensor is plugged in or not, then i tend to think it is not the sensor



not likely the chip or airbox.

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[dry664]

Cheers Flash.



What about the throttle plate?

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[flash]

the throttle plate should be essentially closed at idle, and all of the air coming in via the ICV.



this may seem counterintuitive, and you may think that an open throttle plate would make it lean, but actually it's the reverse. if it is open, then the ECU is going to think that the engine is under more load than it really is, due to the increased airflow, and it will add fuel to match the load it thinks is there. when cold and at idle, it could easily make it very rich.

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[dry664]

One last question. I did try and follow the test procedure in the attached with two different <acronym title='throttle position sensor'>TPS</acronym>', lowest voltage I could achieve was 0.46V. Is that likely to be an issue?

http://www.968forums.com/topic/11765-thr...ntry118910

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[flash]

it should read about .5V at one extreme and about 4.7 at the other

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[Bulti]

"O2 sensor is old but I believe the car doesn't start taking data from the o2 sensor until its warmed up? Ive run the car with the O2 unplugged, still has the stalling issue."



Flash, I read somewhere that the coolant temp sensor essentially shuts down the other sensors from influencing the air/fuel ratio until the temps are high enough and the risk of running too lean (by adding more air) has gone away.



But you say it is controlled by a timer of some kind. That's a bit strange: if it's freezing outside, wouldn't it take more time to heat up than in case it's, let's say, 10°C?

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[flash]

not according to the data logs i have watched as i was tuning. they showed everything sending a signal.



every time i did a cold start, it took almost exactly 60 seconds for the mixture to go from rich to stoich. it was really interesting to see it too. it was as if somebody flipped a switch. it would run rich for 60 seconds, and then abruptly start leaning out, taking only a few seconds to hit stoich.



that being said, if it were colder outside, it might take longer after the "switch" was flipped to get down to stoich. here in 70 degree weather, it only took 5 seconds or so. in 10 degree weather it would probably take a bit longer.

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[Bulti]

Interesting. So most other cars would use the method I mentioned above to prevent damage from running to lean? Why does our car work differently?



Many questions, I know :-)

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[flash]

not sure other cars would do what you describe either. emissions standards require that a car pass on a cold start. that would preclude any significant mixture meddling. i went through this when i was getting the CARB certification.



yes, precautions would be taken to prevent detonation, but more likely it would be timing retardation more than fuel fattening. other sensors would get involved to determine the time at which things could be returned to "normal". however, fattening things up at startup became a lot less common every since fuel injectors and electronic ignition came into play. decades ago you would "choke" the engine until it was warm. it isn't so much the case anymore. like i said, only the first 60 seconds is rich, and even that isn't that far. i would have to do some testing, but i think that is how long it takes for the O2 sensor to be fully warmed up. it would certainly seem to be the case, as the mixture really leans out right after that period.



on the tiptronic cars, there are further precautions which limit the programs in the transmission until it is warm.

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[flash]

a thought occurred to me while i was pondering this one. way back when i first started talking about the airbox mod, i told everyone that in really cold conditions that it might run rough until warmed up. this is the nature of the larger amount of cold air, and the immediacy of it hitting the MAF.



i would try closing off the 4 ports in the box, and see if that makes a difference. take care not to let whatever you use to close the ports from getting in there and getting stuck where it completely blocks off the air.

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[Bulti]

"emissions standards require that a car pass on a cold start."



Over here we are required to arrive with a fully warmed up vehicle when going for our annual emissions test. The invitation we get from the testing station mentiones it literally.



What makes me wonder is how diesels can pass emmissions over in the US. These engine's emissions are through the roof when cold...

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