My 1999 E150 van has periodic problems running at an idle. I have researched this and have come up with three possible problems:

* EGR Valve
* EGR Solenoid
* Idle Speed Control

Does anybody have any idea which is most likely to cause the problem?

 

I believe the first thing to try is cleaning the throttle body.

 

Sounds like the IAC - Idle Air Control motor. It's less than $40 for a new one.

 

You need to be much more descriptive in your problem - but one of your three guesses is probably right. To distinguish a tune up problem from a power train management problem (IAC, EGR, TPS etc) you need to know when the idle problems occur and how they are characterized.

 

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9 times out of 10 it is a dirty or failing IAC that isn't moving fast enough and will allow the engine to stall.