Chrysler Repair: 93 3.3L wont idle when warm, coolant temp, dependent problem

Question
QUESTION: History- '93 Grand Voyager. Cylinder head was R&R. Now van will start and idle fine until the engine temp reaches 200 (via Auto-Xray unit). At this point it begins surging (very low up to about 1500 and back, around 2 second cycles)and eventually dies.
When I disconnect the MAP (driving it back into "limp" mode?) it idles smooth as glass.
The EGR valve moves smoothly and appears to seal well, the TPS moves smoothly and reads 38 to 486 ohms (other side is same), AIS is clean.
I replaced the MAP but see no change.
I am suspecting a loose/disconnected ground but don't know where to look for these.

ANSWER: Hi Bill,
You didn't mention whether you tried for fault codes using the ignition key:"on-off-on-off-on and leave on" doing that in 5 seconds or less elapsed time. Then watch the check engine light, which remains 'on', to see it begin to flash, pause, flash, etc. Count the number of flashes before each pause. Then repeat to assure an accurate flash count and let me know the results.
Have you followed the resistance of the coolant temp sensor: it should start at around 4,000 ohms and steadily drop to around 1,000 or less at operating temperature. It might have air trapped in the thermostat housing which would throw off the readings, or the sensor could be inaccurate. That would be the area I would check next for the temperature-dependent problem.
Roland
PS Please 'rate' my answer and consider giving a 'yes' where you see the question about a nomingation of me to be 'volunteer of the month'. Thank you

---------- FOLLOW-UP ----------

QUESTION: On the Auto-Xray it comes up with "No trouble codes" every time.
I will try the temp sender unit but the Auto Xray shows that it progresses smoothly (as does the dash gauge). Is there another temp sender unit to check or only the one on the forward head near the pulleys?
I have driven it about 25 miles so I doubt that there is air under the thermostat but I will try to check.

Answer
Hi Bill,
For the '93 3.3L:
The temp sender that impacts the mixture is located next to the thermostat housing on the top of the engine. A separate gauge sender is on the front of the engine. So check out the one near the thermostat to see what it reads in ohms at 200F. In later years the gauge sender was eliminated when the cluster went 'digital.
Roland
PS Please 'rate' my answer.