911 Engine Cut Out

[RDS137]

I have an 84 3.2. Engine runs strong on start up. Good for 20 minutes or so, come to a stop or significant slow down and the RPM's drop quickly and vehicle stalls instantly. Sometimes starter engages right away, other times takes many turns for car to start. Key turns, dash lights come on, just feels like there is no engagement. Voltage remains constant and the battery and alternator are relatively new. Problem is somewhat intermittent.

Any suggestions would be helpful. I did have part of the ignition replace last year, maybe I did not get to the root of the problem.

Thanks

[scarceller]

Is the idle switch on the throttle body working?

You can easily test it following this procedure:

- engine fully warm and idling. The 84-85 cars idle at 800RPMs, does it idle at 800?
- The idle switch connector is on the RHS of the Throttle body. It's the 2 pin connector, locate it.
- With engine at idle fully warm, unplug this connector. The idle speed MUST increase to above 1000RPMs. If you unplug this connector and nothing happens to idle speed then the idle switch is bad or not properly adjusted.

Report back the findings.

[T77911S]

DME relay.
probably a bad solder joint,
as the relay heats up it stops working,

if you can solder i would pull it out and inspect it. look for a small line around the solder joints.
if you cant find it then just resolder all the joints.

check for spark when it wont start

[scarceller]

Yes, possibly the relay.

To test this quick when it won't start, in addition to testing for spark also turn the key to 'RUN' but do not start the engine. Then go in the engine bay and see if the Idle Control Valve is vibrating and humming. If it is not then the DME is not booted up and running. Could be the relay.

The description of the problem sounds like an idle issue when returning to idle, is this correct? It only stalls out when you lift off the gas and allow the engine to return to idle? If so you must verify all the idle components. Idle Switch, Idle Control Valve and the base idle speed needs to be checked. The 84-85 cars idled at 800RPMs while the factory bumped the idle speed up for 86-89 to 880RPMs. The factory realized the 800RPM idle speed was simply to low. This causes the 84-85 engines to be very temperamental at 800RPM idle.

Originally Posted by T77911S

DME relay.
probably a bad solder joint,
as the relay heats up it stops working,

if you can solder i would pull it out and inspect it. look for a small line around the solder joints.
if you cant find it then just resolder all the joints.

check for spark when it wont start

[Steam Driver]

Another idea on this.

A friend of mine had a similar situation with his 3.2. The problem turned out to be a restricted air filter! It was one of the blankety-blank K&N’s but I suspect it could happen to a stock installation as well.

Seems odd, but I think what is happening is that the ECU is getting mixed signals in that the AFM isn’t passing the air the rest of the sensors are wanting and it just throws up its hands in disgust!

[gomezoneill]

How many miles? Maybe the reference sensors are starting to go bad.