Chrysler Repair: 2000 Grand Caravan Transmission, auto tranny, professional mechanic

Question
After van (with 3.8 and 4 speed auto tranny)has been run a while and stopped in gear (waiting for a light), the van surges as though the engine idle is jumping.  Is this a tranny problem or an engine speed problem?

Answer
Hello Allen,
I have not heard of the trans being the cause of that sort of behavior, but I can't be sure. I would do two things:
Find out what the idle speed is when the trans is in neutral and the van is trying to do the surge. If you don't have a tachometer on-board you may need to get an inexpensive one or ask a friendly amateur or professional mechanic if he would use his meter for you for free (it takes about 1 minute). Then compare that with a specification on the underhood sticker (if it is given there) or if not, I would say that if it is under 1,000 rpm the idle speed is o.k.
The other possibility is that the idle speed is not being held at that low level reliably (it may only happen once in 5 minutes, or at random). The most useful thing to do would be to try to get the engine contoller fault codes that may be stored in the engine controller memory to readout. Try using the ignition key: turn it "on-off-on-off-on" and leave it "on" (doing this quickly, no longer than 5 seconds). Then watch the 'check engine' light to begin flashing, then pause, flashing, pause, etc. Count the number of flashes before each pause and keep track of the numbers. Repeat the readout and verify the counts are correct. Then group them in pairs in the order that they came out, thus forming two digit numbers. You may notice that the pause is shorter between the digits of a given number, and longer between the numbers themselves. Then send me a 'follow-up' question telling me the results of your readout. By the way, 55 will be the last number (two groups of 5 flashes each) and that is the code for "end of readout". Code 25 would indicate a trouble with the idle speed control circuits.
There is also an essay on fault codes at the site:
http://www.allpar.com/fix/codes.html
which gives the meaning of the code numbers. But then you need to get specific info for what exactly might be the diagnostic tests or parts to replace to complete the repair.
Roland