Replaced PCM on 2004 Ford Frestar - now occassionally chugs and idle surges

Maintenance/Repairs
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1

I recently had my PCM replaced because it got wet. Now, my Freestar will occassionally chug while driving around town, and every now and then while idling the engine’s rpms increase to about 1400 and then drop back down to 500 rpm (normal idling rpm for this engine). I run Seafoam through the gas tank every 3rd tank, and had new plugs put in per routine maintenance. It has 88,000 miles. Any idea what’s up?



Thanks!

2

How did the PCM get very wet? How many electrical connectors (like the PCM connector) got very wet?

3

According to Ford, the PCM got wet because of s design flaw where the enclosure was located just below where the water runs off of the windshield, and the enclosure wasn’t water-tight. There is a TSB about how to seal this up if the PCM gets wet. Well, my PCM not only got wet, but it failed as well. After the PCM was installed, the Ford mechanic put it on their diagnostic computer and did not receive any error codes, and the van ran perfectly for about a week. Keep in mind that the van runs well now about 98% of the time - these are intermittent and occasional occurrences over the past couple of days only.

Thanks, again!

4

I would start with a careful check of the connector (on the car’s wiring harness)that plugs into the PCM.

5

I’ll try that Tardis, thanks!

What are the chances this is an unrelated issue that coincidentally surfaced now…such as a bad plug wire? How would I perform some simple “driveway tests” without digging in?

6

I know this follow-up is a bit late, but I just had another problem diagnosed that I thought may be useful. I just had the Freestar into the Ford dealership for yet another “Check Engine Light” issues, and my coil pack was cracked in 4 places! Thought those who were following this thread may want to know.

7

Thanks for the update, Sutherfam. A cracked ignition coil isn’t one of the things which come to mind when there is an engine surge; but, stranger things happen, inexplicably.
If the engine surge returns and/or a check engine light comes on, bring the problem/code here for discussing and cussing.