Is It A Misfire or Problem With Engine Mounts?

We have a 2000 Windstar LX w/ 3.8L and 121,000km.

The tranny was just rebuilt. when we got it back, I noticed it feels like it's misfiring. It feels like a mild vibration, not constant, but cyclic.

I cleaned the IAC a few weeks ago.

The plugs were changed last year, I'll change those.

I plugged in my code reader, but I didn't get a misfire code. There are no codes. I read the codes twice.

Acceleration is nice and smooth.

Could the removal/installation of the tranny have affected the engine mounts? How can I check the engine mounts?

Thanks.

First of all did you have this problem before your transmission was rebuilt? Was the van vibrating before the transmission needed a rebuild? If the problem started after you got your van back I assume it has soemthing to do with the transmission. It sounds like you have torque converter shudder. Does it happen when taking off from a stand still? Does it vibrate when shifting into 4th gear? Did ford rebuild the transmission? This ax4s transmission should only use mercon V not mercon. Also was the torque converter changed when they rebuilt the transmission?

The problem wasn't there before the tranny was re-built. The engine was actually running pretty smooth before the tranny broke.

The vibration can only be felt at idle. It feels like a mild misfire, but even a mild misfire should give me a code. There's no code. Vacuum lines are ok. IAC is clean and working.

The tranny was rebuilt by a reputable National chain specializing in trannies. The tech owned the shop and he has a good rep with the other mechanics in the area. I researched him first before deciding to have him fix it.

The van goes back in a week for a post fix check-up. He wants to re-check for leaks and other symptoms (no-charge). I'll bring it up with him then. I'm hoping it's just the engine/tranny mounts.

So many possibilities........you mention that you notice this ONLY at idle...
Do you feel this with the transmission in neutral or park?......or just when it is in gear.
If you still feel it when it is not in gear......it reduces the possibility of it being the transmission.
It could be a slight enough of a misfire that it is not causing a code to be set (yet).
I had that a couple times with my '96, which was prone to get dirty fuel injectors (only Berryman's B-12 Chemtool would clean them up).
A vaccum leak can cause the same thing.......
Also, clogged EGR ports in the lower intake manifold can cause this.....but should not cause it at idle.....but while under way (when the EGR system is activated).
Again....vaccum leak and EGR port issue could still be slight enough to not cause enough of a misfire to cause the CEL.

Another possiblility is the coil pack.....which seems to be problematic on the newer windstars.
Plug wires also.
If you replace the spark plugs......stick with Motorcraft or Autolite brand of DOUBLE platinum.....that is.....Platinum on both the center electrode AND the ground tab.
Stay away from those multiprong Bosch plugs........seem to not be well suited for the Windstar....can cause misfire right out of the box......likely due to the negative spark on one bank of cylinders and a positive spark on the other.

I find the Windstar engine mounts to be very rugged and would expect they will never require replacement under normal survice. Who know what may have been overlooked or loose during a tranny reinstallation. I would expect your mechanic will be able to locate the noise if you can demonstrate it to him.