1986 3.2 quits below 1500 rpms

[Amberjack]

Long time 911 owner (this car), new poster on the forum. A few years ago the car developed a stalling issue at low rpm's. Two different mechanics haven't been able to solve the issue but it can't be unique to me. I'm hoping another 911 owner will recognize the symptoms described below and tell me how they solved it.

1986 Carrera 3.2 130,000 miles strong reliable engine except for this problem

Car runs fine in warm, dry weather
Stalling issue happens in cool or damp weather
If I can get it running and drive it long enough to be thoroughly warmed up the problem usually disappears

On stalling days car starts harder and engine sounds different. I can't really describe it, it just sounds or feels different. I can get it out of the garage by keeping the rpms high but the engine quits when rpms drop below 1500, with or without the clutch engaged, in or out of gear, doesn't matter. This isn't really a stall, it just quits with maybe one or two pops at the first intersection. Once it stalls it is very hard to restart and will only restart after sitting for 15-30 minutes and then continues to quit below 1500 rpms. This is not a gradual thing, the engine runs OK above 1500 rpms but as soon as the rpms drop below that it stops abruptly.

New in the last 8 years:
flywheel
distributor cap and plugs
head temp sensor
idle stabilizer valve
new fuel filter this summer and all fresh ethanol free gas

Seems like this must be a component that controls low speed rpms and is sensitive to cool or damp weather but mechanics haven't been able to diagnose it.

[proporsche]

it looks like you have 2 problems..
2nd problem is possibly your fuel pump check valve.it is supposed to hold the fuel pressure in the system...
1st problem .where do you live state?? climate wise..

Ivan

[911obgyn]

Pop distributor cap off and have a look, carbon tracks, moisture, loose wires, wiggle plug wires and at coil.
Get a can of starting fluid and when it won’t start spray a bit in the intake and see if it fires, if it does it’s a fuel issue.
Check idle switch per Bentley manual. You can hear it click just as throttle opens before you start it.
Check the 3 plugs on the left, head temp, and 2: crank sensors make sure they are not loose.

[Dan Owens]

I would be looking at the components that operate or control your engine at idle, since the engine runs fine at higher RPMs. ICV would be the first place I would look to make sure it is operating correctly, although I think you indicated it was replaced??? If it's clogged and partially operating it can cause you exact issue. You already changed out the CHT sensor. Also check the AFM for proper operation as it can cause similar issues. Also check the closed throttle switch for proper operation,( my bet on this).

[Amberjack]

Thanks for the support guys, it feels good to have some direction where to look.

Proporsche--Seattle, where its cool and damp 9 months of the year therefore the car is not reliable 9 months of the year in its current state

911obgyn--we've been all over the distributor cap, replacing it, sealing it against moisture and keeping it dry during storage. I understand this was an issue with 86 & 87 3.2's. I'll get to work on the other items you suggested

Dan--yes, the idle control valve has been replaced (at least I was told it was, I'll check it). AFM and closed throttle switch are next up. 'Closed Throttle Switch'-- hmmm, if words could describe a component causing this issue that would be it!

This is a beautiful car, 1986 911 3.2 M491 Moss Green and a heck of a lot of fun to drive. I need to get it back on the road.

[Dan Owens]

Here's a link and short blurb about the closed throttle switch and some test info for you. The switch can be failing intermittently so a test of the switch may not show anything unless the issue is occurring at the time. Intermittent problems like this can be very frustrating to find. The part isn't terribly expensive. inspect the connectors also as they can degrade and become brittle and have cracking which can also cause issue separate of the internal operation of the switch.


https://www.porscherepair.us/porsche-911-1984-1989/throttle-position-switches.html


Keep us posted of your findings as you work thru this. It may help someone else and because we're noisy! We may also be able to provide additional feedback to help

[jpnovak]

Have you opened the AFM and inspected the carbon wiper tracts to make sure they are not worn?

Here is an example.

Air Flow Meter (AFM) Operation and Testing

https://forums.pelicanparts.com/porsche-911-technical-forum/1032105-air-flow-meter-adjustment.html

I expect they are worn and causing issues.


It could also be that your coil is failing.

You can use a timing light to verify if the coil shuts down during your hard start conditions.

[jlex]

Sounds to me like your idle isn't adjusted properly. Must first jumper the port on the left side of the engine (near coil) to take the idle stabilizer out of the loop. Set it to proper idle speed. After the jumper is removed, the idle with the idle stabilizer valve now enabled should match idle with the jumper intact. Do a search to find out which two terminals you need to jump.