2.9L Merkur Scorpio - Off idle hesitation when cold

[brokencase]

So desperate I've jumped to you Ranger folks for advice, with the hope that your greater numbers would mean that someone with a Ranger might have experienced this.

1988, 89K miles.

Symptoms - When starting up at ambient, engine will have a hesitation or stumble when you stomp on the throttle.
Sometimes it may back fire on a very rapid stomp. Condition subsides as the engine warms up turning into only a very tiny hesitation.
No issues if throttle is slowly opened.

No EECIV codes issued.

To address the issue I replaced ACT, ECT with quality Delphi items.
New old stock MAP swapped in.
Swapped TPS with spare, no change.
New Cap and Rotor. New rotor has brass post. Old one had aluminum - don't ever buy the aluminum ones!
Verified timing at 10 BTC with SPOUT removed.
Fuel Pressure : 45 psi KOEO, 35 psi running at idle.
Throttle body and IAC have been cleaned.
During KOER test the EECIV changes idle with IAC and that seems to be running correctly.
Extensive exploration for vacuum leaks. Used propane to look for leaks. Clamped of all vacuum lines to manifold to see if the situation would improve - it did not.


Other items that have been recently replaced (within the past 2 years.)
EGR new and tested OK. New PFE sensor and EGR solenoid.
New Bosch ign wires
New O2 sensor
New Fuel Pressure Regulator
New Fuel Filter
New CAT and "Borla CAT Back" stainless exhaust fabricated.

This doesn't leave much. Fuel injectors? TFI?

I sure would like some way to verify injectors are the issue before I start ripping the manifold off.

 

[brokencase]

I think I found the problem...

It was the Idle control solenoid. I had previously cleaned it, but I did not test it.

With the IAC removed I took some tubing and I blew through each port. I noticed no restriction when blowing through either port.

I then removed the solenoid from the valve itself and then rotated and seated the valve. I then noticed that on one port I could not blow through. Which is what I expected.

However when I re-attached the solenoid the the valve the valve was slightly pressed open again.

So what I did is added another O-ring between the valve and the solenoid such as the valve remained closed.
Started the car and the hesitation problem is gone.

There appears to be a spring in the valve and a spring in the solenoid. I think the valve's spring is worn out.
So it can't keep the valve closed against the spring in the solenoid.

So I am going to look for a new IAC.

Anybody ever run into this?

 

[Paulos]

The Ranger/B2 2.9's don't have an ISC, unless your talking about the IAC. Usually (from my experience anyway) a bad IAC results in a high idle. Basically a vacuum leak.

 

[brokencase]

Correct - I meant IAC - Lets be explicit "the solenoid valve that bypasses air around the butterflys" OK? It was essentially a vacuum leak. Upon cold start the EECIV was enriching, but since the we had a slight vacuum leak this is why it stumbled when cold. As it warmed up this became less of an issue since the EECIV begins leaning out the mixture anyway.

The leak was small. When I performed KOER test the EECIV it had no trouble during the phase where it changes the idle with the IAC.

 

[brokencase]

Actually I wasn't off in my initial "ISC" terminology... They just changed it in 1993...