1988 924S will hold an idle and stalls out

[solex3274]

After replacing a number of old rubber hoses under the intake manifold this winter and putting it all back together, the idle surges to 3000 rpm when started then quickly stalls out.

The following has been tested:
1. Tomming belt correct, all marks line up.
2. Compression test, all four look good.
3. Wires and cap on right, spark to all 4 plugs
4. Did not do a fuel pressure test, but pulled the rail and cranked the engine. All injectors spraying nicely.
5. Plastic vacuum hoses all connected

I think the source of the problem lies in the manifold area. How do I test the Idle speed Control valve and the Air Flow sensor to see that they are actually working? Any suggestions welcome.

[John_AZ]

Usually a surge is a lot of air getting into the vacuum lines.

Start at Clarks Trouble Shooting page and then the AFM information for ideas:
Troubleshooting - Engine

It is real easy to have a hose come off under the manifold when replaced.

Were the AOS seals replaced?
Did you replace the rear hose to the ISV? The short hidden one under the intake.

New injector gaskets and FPR "O" ring? (Same as bottom injector fat "O" ring)

Under the air intake boot is a plastic vacuum line connection---gets brittle and cracks easy.

Check all hoses and clamps for tight connections.

EDIT--Remove the AFM connection and check the pins. Clean and make sure the connection is tight.
GL
J_AZ

[jpk]

My '85.5 was doing this. Would start and run well for a few seconds, then die suddenly. Blipping the throttle had no effect; when it decided to die, there wasn't anything I could do to change the situation. I could re-start it right away, it would run a few more seconds, then die again.
I swapped the DME and the problem went away.
Check the obvious stuff first, but it might be time for a brain transplant. I was able to use a borrowed DME for a while, but I just recently swapped my original one out for a rebuilt from ecu doctors in Florida.

[solex3274]

Thanks for the suggestions, I did use a multimeter and there is voltage in the harness going to the air flow sensor and the throttle switch. That tells me the DME is working.
However it looks like I am at the point that I have to start throwing parts at it, something I would rather avoid.

[Chunkerz]

Have you tried bypassing the ISV? You can unplug it from the j-boot and cap off the vacuum line/hole in the j-boot with your fingers while someone else starts the car. You can also use some small corks to plug the hole in the j-boot/vacuum line going to the ISV. Just make sure they're big enough to not get sucked in. If you don't want to try those, you can jump ports B&C on the test port to the right of the brake booster (looking at the front of the car) or just disconnect the ISV, but that's almost impossible with the intake on. There's more info on Clark's Garage on bypassing/testing the ISV.

Any moisture/cracked solder joints in your DME? Just because the AFM is getting power doesn't always mean the DME is working correctly. Have you tried another DME? Are your speed/reference sensors working properly? TPS working/adjusted correctly? Have you tried pressurizing your intake and listening for leaks? I don't have the video handy, but if you search on YouTube Van posted a video about it how to do it.

Edit: ISV info:
Idle Control Valve Testing Procedure
Idle Valve

Speed/reference sensor testing:
http://www.clarks-garage.com/shop-manual/ign-02.htm

TPS checking/adjustment:
http://www.clarks-garage.com/shop-manual/fuel-06.htm

DME cracked solder joints info:
DME Bad Solder Joint Repair

Intake pressurizing to check for vacuum leaks:
http://www.youtube.com/watch?v=AL3jbcrqY8g
The car in the video is a turbo, but it'll work on any version of the 944.