Idle issue's

944mech · 944mech's Garage

Lately my '83 944 has been idleing really rough and seems like its missing. It does a sort of a bogging sound and it will die if I dont hold the gas. It revs and drives perfectly fine after its gone past the 2k rpm's mark.
But under 2k and closer to 1k rpms it is horrible and will die if I let go of the gas. Ive adjusted the the idle screw, toyed with the wilks chip back and forth from stock to chip, toyed with the adjustment settings on the side of the DME and it just changes the problem a little bit.

Its not the air bypass valve under the intake manifold and almost everything is new or repaired.
I think it may be the DME going bad or maybe the AFM is going out.
Could it be the reference sensors?

There is a bad wire going to the AFM that could be causing this, because if I wiggle the AFM wire when the car runs it causes the rpm's to drop imediatley and almost die if I dont hold the throttle.

Any idea's?

Razorback1980 · Razorback1980's Garage

I think you called it pretty well with the wire. Fix that first as it definitely needs it. Second, the problem should not be with the DME or the reference sensors. The reference sensors do set time I guess but the default timing should idle fine but have problems at higher RPMs. It sounds to me like you have a vacuum leak. When was the last time all the vacuum lines were replaced under the intake?

1988_944 · 02-10-2007, 09:08 AM

Check all the vacume lines, and air intake hoses. U may have a leak or a loose connection, You can also adjust the idle up a tad.

944mech · 944mech's Garage

I did the lindsey racing vacuum line kit when I rebuilt my top end last summer so those are all done. Im going to replace the hoses that run down by the intake box and under the manifold, the fatter hoses that the venturi is connected to.
Ive set the idle the best I could at about 1100 because anything below that it vibrates and is quite annoying. I probly need motor mounts but just getting the car running is more important at the moment because of school.
Im going to use some propane around the engine bay and see if there are any leaks before taking things apart.

SoCal Driver · SoCal Driver's Garage

Check the J boot between the throttle body and the AFS -- including the large elbow connection on the bottom. J-boots tend to come loose at the throttle body and AFS flange.

You could also have a loose intake manifold or an o-ring around the base of the injector.

944mech · 944mech's Garage

I just replaced the injectors and orings with brand new ones.
I'll check the J-boot.
Could an alternator cause this? Maybe a faulty regulator?
The alternator is original.

SoCal Driver · SoCal Driver's Garage

There can be many causes. Best to go back over the most recent repairs and check all items removed and reassembled. Read the last line in my signature.

944mech · 944mech's Garage

Well, my dad found out that if you hold the AFM wire just right it'll run perfectly fine, so I ziptied it to the air hose next to the airbox and so far its running great.
Both cold and warm idle are back to normal.
Im still going to rewire that section of the harness but at least it runs, for now.
Stupid old brittle wiring!!!

1988_944 · 02-10-2007, 12:52 PM

Good Job. Nice trouble shooting.

Razorback1980 · Razorback1980's Garage

Make sure the AFM connector is clean first...it may be that by moving the wiring you are moving the connector and reestabling a connection on one or more wires.

944mech · 944mech's Garage

I pulled off the connector and made sure they were tight and clean. The section that has a problem with it is under the intake manifold, so I may have to pull the manifold off.

Does anybody know if it's possible to get new connector's for the AFM, TPS, and water temp sensor?
I may make a new harness from the computer forward and make it better than the original.

Razorback1980 · Razorback1980's Garage

The problem may not be with the AFM wiring, it may be with the TPS. Check those connections for that switch for tightness as well. I am not sure if you can buy those connectors or not, but I suspect that you can. Look them up on PET and they should have part numbers that you can use to order them. They may be the ones listed in the last section of electrical but they only show them by color and number of connections.