2002 Windstar Surging Issues

I am helping a friend with her 2002 Windstar 3.8L. It has had issues which I originally thought was the 171/174 issue, but don't know now. Now, with what I've done, it surges and will almost die at idle (whether in neutral, park, or drive) and will like to surge hard in drive when you step on the gas. I have done the following:

What I've done:



Changed plugs and wires ... old plugs were gapped all over the place, from about .080"+ to under .030" ... one of the wires was in contact with an exhaust manifold, so assumed it was bad.
Changed the IAC
Checked EGR ... works correctly and not slogged with oil
Fuel pressure is at 42psi at idle ... read it is supposed to be between 35-45psi, I believe?
It appears it has the newer valve cover (so should not have excess oil into intake manifold issue)
Checked operation of the tps ... appears to be smooth ohm transition as it should, but really hard to tell. I read online there should be a way to check voltage at .9v between two places (89 & 90) I believe of the "breakout box" ... I have no clue what this is supposed to be or where it is located.
No apparent vacuum leaks, though would be hard to tell for sure
It appears the O2 sensors are working correctly as I'm getting plenty of movement.

Next thing I'd like to look at is the TPS, but am unsure on how to test it. Do you read the voltage directly at the PCM or where is this "break out box" I've heard spoke of (or is the PCM what they are talking about??). The TPS reads 18% at idle (as read from a hand held OBDII reader live data), which seems very odd to me. Mine line of thinking says it should read 0% at idle. If this is an issue, it could be what is causing what's wrong.

If that does not pan out, I'm thinking the isolator bolts need to be changed, as this could easily be the problem. I just don't want to tear the top end apart to see if this is the issue before I check everything else.

What do you guys think?

have you put a vacuum gauge on the motor? I know from experience there are a lot of turns and elbows that are suspect to leak and need close inspection. I'd be checking that to make sure the vac is ok. I'd also make sure the IAC is functioning properly, sounds like you did that but just to make 100% sure. I can't offer any advice on the TPS--hopefully someone else will chime in.

Yes, I installed a new IAC on it. This actually improved (along with the wires & plugs) how the engine runs. It has much more power than it did before. I don't think the IAC had much to do with the power, but it's doing better, so not a step back :)

You may need to do a bit of cleaning: ... the throttle body and throttle plate, ... and the MAF sensor.

Already done.

Have you done a compression test? You did not mention a check-engine light. ??

Have you done a compression test? You did not mention a check-engine light. ??

I am not seeing a reason to do a compression test at this point. It isn't low on power (in fact, quite the opposite). When off idle, it runs smooth and strong ... a little too strong in fact. Nothing leading me to believe this is an issue. Besides, those back cylinders would be a true PITB!! Lol!

There is a CEL on, but I haven't got the van back yet to check it. There was one on the first time when I got it, but it was only a cylinder misfire code. After I cleared it, it never came back. I figured it would have been gone for good after I found the burnt plug wire.

That code would sure help with the diagnosis. Anytime there's a misfire I'd check that coil pack real carefully.

Don't hide the weeney! Get the code!

oh ya, if you've got a code.. find it out!