83 944 NA only runs when ignition is in start position

[gilmore27]

I have an 83 944 NA that's been sitting for a few years. I've been dealing with a no start issue. it would turn over, just wouldn't start. I finally got it to a point where it will run only when the ignition is in the start position. As soon as I let it back off the start positions it dies. If I keep it in the start position the engine sounds good. It responds well with the throttle. I don't do that for long fearing damage to the starter, less that 20 seconds.

Here's what I did so far to get it to this point.

replaced fuel pump and filter
fuel pressure checks good at the rail with a gauge
cleaned, rebuild, and checked the fuel injectors
replaced coil and spark plugs
reference sensors checked good with an oscilloscope at the DME connector
Replaced ignition switch
Cleaned ground point MPII

also, the tach's not working, Im guessing it's unrelated, but thought id add it in case it is.

I couldn't find an issue like this in this in this or any other forums.

any help is much appreciated.

thanks,
Dave

[jhowell371]

Bad ignition switch? They can crack and cause problems.

[gilmore27]

It's been replaced. I also checked continuity of the old and new switch in different positions and they are the same.
Thanks for the reply.

[gilmore27]

I found that if I disconnect the temperature sensor, the engine runs. As soon as I reconnect it the engine stops. The resistance looks ok at pin 13 to GND on the DME connector (2K ohms). Has anyone heard of a temp sensor causing it not to start?

Thanks,
Dave

[gilmore27]

I got it. At least its better. The AFM was disconnected. It still runs rough and cuts off especially at low rpms, but I think thats due to a vacuum leak. The AFM tested good (using Clarks Garage's procedure). At least now it will run with the key in the ON position and Temperature sensor connected.

now to replace the badly needed vacuum hoses.

thanks for your replies,
Dave