986 stalls at start up - 986 Forum - The Community for Porsche Boxster & Cayman Owners

Hi Forum. Lately my 97 2.5 Boxster has changed behaviour. when starting it from cold I have always been able to just turn the key , without touching there Gas pedal and it would start and settle on 1000RPM immediately now it also starts , but it is going to 800RPM down to 500RPM for a few seconds . sometimes it comes up to 1000 RPM again and settle but other times it stops? If I apply som throttle and keep it 0ver 1000RPM it settles on 1000 RPM immediately. I have changed the MAF ( it had cutouts during driving) and it helped a lot on the driving Plugs are new, air filter is new ,- no error codes. It drives perfectly and also idles fine at 800 RPM when warm ( it feels like there is a little changes in RPM under idle , it fluctuates around 800 ( nothing I can see on the Tacho,- just a feeling) When the engine has been started and been running fore a minute or so , it starts fine without me touching the gas. Any ideas on where to start BR Barthol

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I would check to see if the AOS is working properly.

cold start problem with no codes. I would look at the temperature sensor signal with a durametric or better yet an oscilloscope and someone who is good at reading them. could be a lazy signal from the temp sensor. I was going to say do the same with the MAF sensor but I see you changed it out. These are just guesses on my part. But given it is a cold start problem with no codes it is where I would start. just thought of this. Very first thing I would do is a vacuum test both dead cold. (see if you can get someone to hold the RPM at a steady level). And warmed up. try to take vacuum readings at lowest RPM the car will run at cold. You could have a vacuum leak this seals up once the engine is warm.

BFeller. how do I check the AOS, can I just check for oil in the pipe connecting to the inlet manifold?

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“A very basic test for your AOS is while the car is running, remove the oil fill cap. If it's very hard to get off due to vacuum draw, then that could be an indication it's on it way out. There should be some vacuum draw but not excessive” I pulled that from another thread after searching AOS Test. A bad AOS can cause idle problems due to its effect on vacumn.

Hi All, Just checked the TEMP sensors Both the intake air temp, the cooling water temp , the engine compartment temp and the oil temp is around 20 deg C , when the car has been standing over night ( the same as the ambient temp. As soon as I start the car they starts to climb, Water and oil fastest intakeair temp is climbing slower together with the enginecompartment temp Temps actually looks fine, and according to the heat up of the engine. For the vacuum there is no significant resistance inn removing the oil cap not cold nor hot? If I start the engine from Cold ( it hs been standing over night) without touching the gas pedal it stalls and dies, on the 6-7 attempt it starts running erratically at 500 rpm and after 10-20 seconds it increases to 900 rpm and runs fine. When it warms up it idles steady at app 750 rpm. If I at the cold start applies the gas and takes the rpm to 1500 RPM and keep them there for a few seconds then it will immediately idle at 900 RPM when I let go. In general the car runs fine , no oil consumption , nice and clean acceleration, gas milage is app 10 km/liter as soon as the car has been started I can restart it without touching the gas?? can it be bad spark/s , Coils acting up when cold?? BR Kim

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Are you reading the temp from your instruments on the dash.? Or from a scanner hooked to the OBD port? if you are just taking readings from the dash you need to hook up a scanner to the ECU via the OBD port. sounds like the signal from sensor to dash is fine but you also need to know what the ECU sees. Do a vacuum test with a vacuum gauge cold and hot. Reading should be 19-21 with a steady needle. I see your in Denmark so you may need to change that reading to a metric number. If that is good I would start looking for things that can affect fuel or air when cold. That car should have a throttle position sensor might want to check that signal with a scanner right as you start it cold, see if it gives an erratic signal. But pin the vacuum readings down first. After you are sure of good vacuum readings try this as a check. with the engine dead cold unplug the MAF sensor (This will force the ECU to go to a set fuel MAP). Try to start the engine. If it starts and idles fine that should tell you it is fuel related. get back to us with what you find.

I had some additional thoughts on your cold start problem. The fact that you have to try 5-6 times to get it to start when dead cold says your fuel/air mixture is to lean for cold start. Engines need a richer mixture for cold starts then they do once warmed up. I am wondering if there is a problem with your throttle body butterfly when dead cold. you say once you bring the RPM up for a few seconds everything is fine. so as a test the next time you try to start it after it has sat over night. Press the gas pedal all the way to the floor then take your foot off of it and see if it starts normal. what I am trying to test by having you do this is to see if the butterfly position in the throttle body is linked to the problem.

Hi All, Just tried to Disconnect the MAF - No changes Tried to take of the pipe going from the top of the AOS to the intake right after the throttle body- There was a little oil in the pipe. I blocked the hole in the intake where the pipe connects, and the engine seemed to start immediately I guess that the AOS and the pipe going to the intake is a good place to start ? All my temp readings is from the durametric sw:-) I have tried to press the pedal all the way down a couple of times before attempting the "cold start " without any changes in the outcome BR Kim

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Starting to sound like a faulty AOS is creating a vacuum leak. A possibility that BFELLER pointed to. A simple vacuum test would have pointed to excessive air (vacuum leak) versus not enough fuel. Either one would create a lean condition. So cold start problems. But a vacuum test tells you which direction to look. I am not up on the AOS system so I can't help you much on it. I do know that a small amount of oil in pipe going to the intake is normal. You could do another "dead cold" start with the AOS pipe removed and the hole plugged just as a proof. As I have read that replacing the AOS is not that much fun Keep us in the loop I always like to know the outcome when I am trying to help someone. Helps me learn more

If this car is a non e-gas there will be an idle control valve on it. It is controlled by the DME to modulate the idle speed. It does this by bypassing air around the throttle body with a valve that is opened and closed depending on what the engine needs. If it isn’t working properly it will cause the exact symptoms you are experiencing.

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Cosmo, For my own knowledge: Would you know how to test it for proper function? or is there a signal that can be read with a scanner like the Duramatic?

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Cosmo, For my own knowledge: Would you know how to test it for proper function? or is there a signal that can be read with a scanner like the Duramatic?

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With it being a 97, I don’t think the Durametric will monitor its performance. Will probably just show what voltage the DME is sending to the idle air controller. I would take it off and clean it and see if the condition improves.

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Cosmo, Thank you. Guess I need to read up on it so I know how it works and how it is integrated into the system.

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Any news? My 97's Boxster have the same problem. 😔

Hi Forum, thanks a lot for all your ideas and suggestions. I changed the AOS and the Vacuum line going from the top of the AOS to the inlet near the throttle body. This cured the issue. Please be aware that I got a newer type AOS where the tiop round part I vertical vs my old one where it is Horisontal. The vacuum line with the new AOS has to be a few cm longer. I initially got the original one which turned out to be to short . the longer one was 996.107.145.06 whereas the older shorter one was 05 at the end. BR Kim

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Thanks for getting back to us help everyone learn from each other. Glad to hear your problem is fixed