86 Carrera - cold start issue UPDATE

[73pcar]

As some suggested in my OP, I disconnected the CHT plug to see if there was a change to my symptoms. With it disconnected, the car would not start after 4 or 5 attempts but there was noticeable 'rich' fuel smell. So, I re-connected the plug and it started but still had to feather the gas to keep it running...initially for about 20 seconds very rough from the obvious extra fuel in the system then it cleared up fine. I am inclined then to swap out the CHT. To refresh, my initial post the other day began because during a cold start the engine would fire immediately, go to 1K rpms then immediately die...and it would do that repeatedly unless I then applied some pedal to keep it running. After 20 or 30 seconds it would idle just fine around 1K rpms...very smooth idle from then on and when running hot as well. There was a suggestion from one or two who responded suggesting some 'carb cleaner' being sprayed (I forget now the exact terminology of where it was suggested it be sprayed but the intent was to obtain a better idle), but again, the idle is perfect with a hot or cold engine....just that first 20-30 seconds I need to keep catch the rpms from falling off. Hope this makes sense and I continue to appreciate everyone's thoughts and suggestions.

[proporsche]

Hi ..i suggest to do one thing at a time..So clean the idle control valve ...then you can test your starting procedure...make sure that when cleaning use a compressor asap to blow the cleaner liquid out...also what was the last time you have check the c/o mixture? fuel and air mix...
Ivan

[cabmandone]

Put this with your original thread.

[73pcar]

Originally Posted by proporsche

Hi ..i suggest to do one thing at a time..So clean the idle control valve ...then you can test your starting procedure...make sure that when cleaning use a compressor asap to blow the cleaner liquid out...also what was the last time you have check the c/o mixture? fuel and air mix...
Ivan

I will do the ICV clean tonight, but I honestly don't understand why that would be an issue....again, the car idles perfectly hot or cold and wouldn't a faulty or dirty ICV exhibit bad idling all the time?. My initial posting mentioned that it was only a 'cold start' issue with the car starting immediately but just as quickly shutting off unless I 'catch' the RPMS with the accelerator before they drop and then engine shuts off. When I do catch the RPMS from falling and keep the car running at around 1K RPMS the idle is also perfect....after 20/30 second it will idle (again perfectly) on its own with no need to touch the accelerator. I'm new to the 86 and appreciate the replies.

[proporsche]

what is your idle speed when warm 800 or 900?
When did you last checked the c/o?
Do you have the oxygen sensor plug in or not plug in?

Ivan

[73pcar]

Idle is either 900 or 1000 rpm...just don't recall, but again, consistent hot or cold. I just purchased the car so I have not checked the c/o but it is a car that has all records and has been consistently and well services. Oxygen sensor is NOT plugged in and was that way when I purchased it, but in looking at other threads on this forum, it seems that is actually a good thing....most agree it yields better performance (more rich than lean) if one can accept less miles per gallon which I'm fine with.

[steely]

Try connecting the O2 and see what happens.
ICV may be needed for finer control when engine is (CHT and O2) cold.
What year again? agree - one thread is preferable

When I got my 87, the ICV drive didn't work, there were small vac leaks, and the O2 was disconnected by the PO who told me it didn't need it. My car was starved of fuel when starting cold (below abt 50 F) until warmed up. I fixed all 3 and the motronic was happy.

[proporsche]

steely ..it is written on top here..... 1986 911 carrera;-)

[adias]

CHT... ICV... Please expand the acronyms for those who do not know their meaning.

[73pcar]

Originally Posted by steely

Try connecting the O2 and see what happens.
ICV may be needed for finer control when engine is (CHT and O2) cold.
What year again? agree - one thread is preferable

When I got my 87, the ICV drive didn't work, there were small vac leaks, and the O2 was disconnected by the PO who told me it didn't need it. My car was starved of fuel when starting cold (below abt 50 F) until warmed up. I fixed all 3 and the motronic was happy.

Thank you for your thoughts and I will go through the ICV tonight, connect the O2 sensor, and turn the key. Sorry for making a new post...thought it would be easier for everyone but guess it only confuses.

[darrin]

73pcar - does your CHT (cylinder Head Temperature sensor) use a single wire (old) or two wires (newer)? If still a single wire unit, you might want to replace proactively (and see if it helps/addresses your problem) -- It's my understanding that the newer 2 wire unit solves a number of issues the older single wire unit (which came with my '86 carrera and failed in the 1990s) had

[cabmandone]

I'm starting to understand why Sal strongly recommends an AFR gauge. It would be helpful to know if the car was running lean due to an air leak that would also lean out the cold start mixture. I think in your original post you mentioned that you barely noticed an idle drop when you removed the oil fill cap. Might be time to take a good look at your vacuum lines and clean your IACV.

adias,
IACV = Idle Air Control Valve
CHT= Cylinder Head Temp Sensor

[steely]

Originally Posted by proporsche

steely ..it is written on top here..... 1986 911 carrera;-)

ahh, merci

[73pcar]

Originally Posted by cabmando

I'm starting to understand why Sal strongly recommends an AFR gauge. It would be helpful to know if the car was running lean due to an air leak that would also lean out the cold start mixture. I think in your original post you mentioned that you barely noticed an idle drop when you removed the oil fill cap. Might be time to take a good look at your vacuum lines and clean your IACV.

adias,
IACV = Idle Air Control Valve
CHT= Cylinder Head Temp Sensor

Thank you. I did not look at the tach to see the RPM drop when the oil cap was removed, but it was indeed noticeable..easy enough to check again to see exactly the RPM drop. I cleaned the IACV last night...will re-assemble it back on the car tonight and before doing anything else will try a re-start to see if the original symptom is still there. Will also inspect the vacuum lines (will look for a diagram that shows exactly where they are) and can ask my tech who helps me on my early 911S to check the air/fuel ratio...just not a tool I have. Thank you all again.

[73pcar]

Originally Posted by darrin

73pcar - does your CHT (cylinder Head Temperature sensor) use a single wire (old) or two wires (newer)? If still a single wire unit, you might want to replace proactively (and see if it helps/addresses your problem) -- It's my understanding that the newer 2 wire unit solves a number of issues the older single wire unit (which came with my '86 carrera and failed in the 1990s) had

Mine indeed is a 2 wire unit. Thank you for the post and idea.

[cabmandone]

Originally Posted by 73pcar

Thank you. I did not look at the tach to see the RPM drop when the oil cap was removed, but it was indeed noticeable..easy enough to check again to see exactly the RPM drop. I cleaned the IACV last night...will re-assemble it back on the car tonight and before doing anything else will try a re-start to see if the original symptom is still there. Will also inspect the vacuum lines (will look for a diagram that shows exactly where they are) and can ask my tech who helps me on my early 911S to check the air/fuel ratio...just not a tool I have. Thank you all again.

I installed a AFR in my car after Sal did some tweaking on my Motronic. The unit cost me $280 and I got a longer cable for the wide band 02 sensor. I figured out my oil cap was off once by noticing my AFR's were off. It's a handy tool to have on an engine worth more than $10,000 currently

[73pcar]

I cleaned and re-installed the ICV...same symptoms as original. I then connected the O2 sensor which has been disconnected since purchasing the car about a month ago...still no difference. So, I guess that might still leave a faulty CHT sensor (unplugging it as another poster recommended only resulted in the car refusing to start and exhibiting a strong fuel smell). Will get to checking the AFR, but if that checks out, then perhaps changing the CHT is the only answer....a few hundred dollar part so I want to be sure. Thanks again for everyone's help.

[pmax]

Why not replace the ICV ? It’s cheap

[cabmandone]

Originally Posted by pmax

Why not replace the ICV ? It’s cheap

Why replace it when in a few minutes and a $1 can of cleaner you can clean it and have it functioning properly?

[pmax]

Originally Posted by cabmando

Why replace it when in a few minutes and a $1 can of cleaner you can clean it and have it functioning properly?

Given cleaning didn’t fix the OP’s issue, are we saying a bad ICV has been eliminated as a possibility ?