Erratic idle and stalling

I have a 94 Cobra Mustang with a 5.0. For the past few months it has had an erratic Idle and stalls when trying to idle. I’ve had a number of suggestions on how to fix it and nothings seems to work. I checked for vacuum leaks, changed PCV, new plugs, new IAC valve, tested ICM and throttle TPS and even adjusted idle. Still no luck. Any other suggestion?

hmmm … you’d done a lot of the obvious things already, sorry so far you’ve had no luck. I’m assuming all the guages work and don’t show anything unusual, no overheating problems, you checked all the vaccum controlled devices for leaks one by one using a vacuum pump/guage gadget, the check engine light is not on, and you’ve had the DTC codes read and there are none current or pending. And if adjustable, the idle rpm and timing have been set according to the emissions sticker under the hood.

Ok, here’s some ideas

Does this engine have a manual idle speed screw used to set the idle speed? If so, sometimes this is used to fix a problem which shouldn’t be fixed that way, and this symptom can be the result. Make sure if it has one, the idle speed screw is set to its factory position. If it won’t idle well when set there, work on that problem, don’t use the idle speed screw to work around it.

Check the compression in all cylinders.

Check the fuel pressure at the injector rail.

Check the EGR.

Check your TPS to see if it is a two part type. One side is a variable resistor, the other side is a switch that is used to indicate closed throttle and WOT. If the switch side does not detect closed throttle, the computer will not attempt to control the idle, it thinks your foot is still on the gas. It also wont set a code for the same reason.

How are you checking for vacuum leaks? It’s possible to have a leak inside the dash so doing this visually does not often work.
If the car were mine, I’d connect a vacuum gauge. This will not only tell you if there’s a leak somewhere but will also provide a heads up about whether or not compression is dropping in a cylinder; or plural.

Losing any coolant? The gasket on the EGR plate can leak and allow coolant into the engine’s intake and in turn could cause an idle problem.

EGR sticking open is another possibility as is ignition timing since you mentioned the ignition module. It’s unknown as to whether the distributor has been removed or turned though.