86 3.2 stalling on decel

[vancouver86/911]

I did the following to my 86 Carrera 3.2:
-dropped the engine and trans
-unseized my clutch lever, replace trans fluid
-replaced both reference sensors and cyl head temp sensor (the top reference sensor was seized right in there so had to take the bracket off and reset the speed sensor depth with a .8mm (.032 inches) washer as per Bentley)
-removed the intake manifold and replaced the gaskets and torqued down to Bentley spec
-replaced all fuel lines with recrimping professionally done
-replaced plugs
-valve adjustment

Start up symptoms:
-started after second crank and then very soon sought 800 rpm and idled steady - the engine was the quietest and smoothest idle I had ever seen on this car-no engine shake and exceptionally quiet (my neighbours would appreciate that)
-once the engine came to operating temp the valves started to make noise again
-when I try to hit the throttle the engine stalls on deceleration
-I let the engine cool down a bit and tried to start it again and instead of
starting right away like it usually does it took two tries and it idled low at
first until it found 800 rpm and stayed there
-it stalled when I first tried to give it gas as well until it idled for a while and then it would accept gas and increase rpm but still stalls on decel
-the ICV valve is new as well and functioned prior to the above work being done

Thoughts? Suggestions?

[efhughes3]

I'd look for a vacuum leak to start with. Did you get all the lines back in correctly?

[vancouver86/911]

I can't find an air leak anywhere. I adjusted the A/F mix richer and now it runs when warm. When cold it accepts gas and revs but when it comes down it drops well past 800 rpm and then stalls. Once it warms up this symptom disappears. If I adjusted the valves too loose or too tight could it cause this cold stalling issue?

[kidrock]

sounds to me like the prior owner may have adjusted the mixture in the AFM to cover up or mask some vacuum issues.

Before you start messing with the AFM, I gotta ask: Have you tried to set the base idle at the throttle body yet?

[vancouver86/911]

When I realized it was now stalling after reinstallation of the engine I jumpered it to disable the ecu and then turned the A/F mix until it ran better and then set the idle to 800. That allowed it to run when warm but it still stalls on decel when cold. The engine ran quite well before I did the valves, changed out the speed, reference and cht sensors and intake gaskets. I'm wondering if I did something wrong somewhere.

[techman1]

Double check the idle switch. Sounds like it is not closing, telling the ECU to take over and manipulate the ICV to regulate speed.

Just a wild guess.

[vancouver86/911]

I'm still chasing this decel stalling issue. It only happens when the engine is cold and it is decellerating. When it gets a little warmth in the engine the car runs great and it just passed the aircare program with no problem so I don't believe it is a mixture problem.
I can hear the idle switch clicking when I slightly open the throttle. I conducted the idle switch test procedure in the Bentley manual by unplugging the idle switch while the engine is idling and it raised the rpm by 500 just as it is supposed to. When I checked the decel fuel shut off function by bridging the terminals of the idle switch and raising the engine rpm the engine did not start surging as the manual stated it should. Any thoughts?

[vancouver86/911]

Suggestions welcome..

[dshepp806]

I'd verify that idle switch functionality with an ohmeter..audible "clicks" bare no electrical information,.....

as well,..I recall Loren speaking of this Bentley test (the increasing 500 RPM stuff) as bogus....search his threads on this....

I'd verify the O2 and CHT sensors for functionality (at least resistance measurements).

BEST!

Doyle

[vancouver86/911]

I checked the idle switch and I have continuity when closed and when throttle is opened no continuity. This was checked several times and and I received the same result each time. The idle switch wiring is getting 5 volts as per the manual as well. The cylinder head temp sensor is reading 2.7 ohms (within correct range as per manual). The CHT sensor is new as are the reference and speed sensors. The O2 sensor is new and is reading .4 volts when engine is warm and it passed the aircare program like this easily. The ICV has the correct ohm readings and I have also switched it with a new one and it made no difference. One thing I hadn't mentioned is the ambient air valve was buzzing loudly right around the time I did these repairs which I believe is a sign it is failing. Would this have anything to do with the car stalling while cold on deceleration?