89 F250 with 351W fuel injected engine, EGR has been removed, plated off, Manifold capped, tubes broken off and sealed, and EGR Eliminator plugged in for computer response. EGR vacuum solenoid, TAB, TAD, removed, electrical plugs wrapped with black tape. I have no emissions, or inspections to worry about.

When started up cold it surges up and down hard, sometimes dying off completely other times almost dies but comes back, when it warms up it calms down a lot, but minor surging still present.

I have noticed that when it surges up high RPM if I unplug the MAP vacuum it idles down nicely, but it still has up and down idle fluctuations.

What does this computer use to determine choking until engine is warmed up?

Any other suggestions welcomed.
Frosty

 

Welcome to FTE. I hope you enjoy your time here.

IAC valve is one possible for what you are looking at. Here's a webpage with technical information- Ford Fuel Injection » Idle Air Bypass (IAB)

One thing we typically tell people is to pull the diagnostic codes. Here's a webpage to assist you with that- Ford Fuel Injection » How To Run a Self-Test You can also get a code reader for a decent price if you're having difficulty with the method outlined on that page- mine I purchased at O'Reilly for about $30 and it will read OBD1 codes for 87-95

With all the emissions stuff removed, be prepared that you will get some codes that are irrelevant for your truck. However you should still get some codes to point you in the right direction.

Given that unplugging the MAP sensor smoothes out the idle, it could also have a vacuum leak. You may be able to find it using a can of carb cleaner and spraying different hoses/connections/gasket areas of the engine, but a better method is to have a vac gauge. When you know what vacuum it should be reading a gauge will easily tell you whether or not there is a leak present.

That's all I've got. Good luck and keep us updated.

 

Good call on the idle air bypass, the solenoid was all but dead, would kind of respond to power sometimes, not at all at others, replaced the solenoid and it purrs like it should. I have no check engine lights at all. i will check for codes this weekend to be sure, thank you.