Chrysler Repair: 1997 LHS running hard, diagnostic capability, engine controller

Question
Roland I have an LHS that the check engine light came on.  I had it in and the service man did a complete tune up plugs and wires and replaced a few fuel injectors.  The light was off for about 2 blocks from leaving the station and it went back on.  The car seems to vibrate on low RPM's.  Once I hit about 2000 or so the vibration leaves.  It seems stop lights and parked are the only times it seems to really be an issue.  They pressure tested all of the cylinders and those are fine as well.  Any idea?  Thanks in advance,  John  

Answer
Hi John,
The on-board diagnostic capability should be taken advantage of in a situation like this. The light coming on means there is a fault code stored in the engine controller. '97 was the year when the fault code system was in flux and some cars had a self-readout capability via the ignition key and others required a plug-in via a diagnotic reader to get the codes. I would suggest theat you give this a try:
The most useful thing to do would be to try to get the fault codes that may 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). By "on" I mean just the normal position when the engine is running, not the cranking position. The 'check engine'light will remain on when you leave the key in the "on" position with the engine still not running. But 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".
I have the troubleshooting manual for several engines and we can look up the possibilities of what is wrong based upon what fault codes you show. When you write back tell me what engine you are driving.
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. If this approach doesn't produce fault codes at all, not even a 55, then you will either have have to go to a good tune-up shop where they have a more sophisticated code reader in order see if there are any codes (you should be able to get a readout for under $50) OR some chain-type auto parts stores will do a readout for free ( e.g. Autozone).
So let me know what the current codes are, and if you happen to know if the shop that did the tune up looked into the codes and happened to tell you what they were.
Otherwise, without the codes, there are many possibilities I could suggest, but that is flailing around when we have a Check Engine light "on" that begs to be decoded.
Roland