Rough Cold Start

[Schulisco]

Not to forget in all troubleshoots - it has a root cause. The challenge is to figure it out....There's neither a ghost, voodoo or sth. else....it's technical and logical engine (IOW deterministic) without any artificial intelligence. For upcoming vehicles (I avoid to say cars...) with AI I'm not sure any more...even on the engine management...but that's another story...

[riparian]

Originally Posted by Schulisco

Not to forget in all troubleshoots - it has a root cause. The challenge is to figure it out....

Indeed! As my favorite youtube Porsche mechanic (https://www.youtube.com/user/irina25661/videos) would say, "Zweig für Zweig baut der Vogel sein Nest"!

[FA-18C]

Rip - from talking to a lot of 3.2 owners, I think your start up is more or less considered reasonably normal. The hunting for idle at start up is a function of the sensors settling in from starting and as the engine begins to warm up. I had similar condition and chased through the system and am down to the fuel pump check valve. Just need to get some time to get under and replace, and hoping that solves my cranking on start. Sounds like you might have some pressure coming out of the system, enough for the start from the solid state priming, but still not fully pressurized, so it struggles until the pump can catch up. That is very much that same on my car. Once it stabilizes above 1000 rpm I can drive, or if I wait 30 seconds it settles to 880-900 rpm.

[LBEEMING]

I had this exact condition. My AFM voltage with barn door closed was about 0.02V. It should be 0.25V.

You can test it with engine off but ignition on. Test lead 2 and 4. Should be 0.25V.

This worked for me anyway.

[riparian]

Originally Posted by LBEEMING

I had this exact condition. My AFM voltage with barn door closed was about 0.02V. It should be 0.25V.

You can test it with engine off but ignition on. Test lead 2 and 4. Should be 0.25V.

This worked for me anyway.

Thanks! I never solved the problem and will check out your solution after I get my motor back in the car (gearbox refresh).

[rbarton]

Originally Posted by riparian

Thanks! I never solved the problem and will check out your solution after I get my motor back in the car (gearbox refresh).

Hi, did you ever find out the cause of your rough initial cold start? My '86 acts the same as what is shown in your video.

Thanks.

[pmax]

No, it isn't normal for the Bosch Motronic (now if you have the Bosch MFI, please ignore this post).

Cold start begins with a higher rpm above 1K if I recall the last few times I drove the 3.2 and gradually settles to a tad below.

[RobFrost]

I think the video is normal. When it starts, oil is cold and lacking in various places. After about 15 seconds, things are better lubricated so revs climb. I'd say the high idle is a normal cold start adjustment by the ecu. Then it settles back to 800. I wish my idle was that stable.

Sent from my SM-G988B using Tapatalk

[riparian]

Originally Posted by rbarton

Hi, did you ever find out the cause of your rough initial cold start? My '86 acts the same as what is shown in your video.

Thanks.

Engine is still out. I decided to also do a glass-out repaint and am now in the process of putting it all back together.

[Schulisco]

How old is your ignition harness? Coil? Spark plugs?

Check out especially the distributor finger and cap! If there are some marks from jumping sparks - this could explain it. When engine is cold more ignition power is required...

Thomas

[riparian]

I finally got my car back together and can report back. Thank you to everyone that tried to help diagnose the issue. It idles as expected now.

With the engine out, I found the problem was most likely this pipe (930-110-328-05) circled in the image below, which our host has available for a mere $237.00. You can see my shiny new one installed (motor is in process of being refitted in photo).





Mine was both swollen at the hose, and cracked in half where the rubber hose meets the compression fitting. It was very hard to see/diagnose behind the heater blower (before I removed the blower for my heat and exhaust backdate). I discovered how bad it was once I had the engine out. I did not find anything else that I thought was bad enough to have caused the issue.

Thank you to everyone who tried to help diagnose the problem, and for those of you with a similar issue, perhaps this will be a good lead.

[pmax]

Congrats on finding the root cause to your idling issue.

Vacuum routing