Chrysler Repair: 1996 Sebring JXI 2.5 stumbles when warm, coolant temp, wd 40

Question
Roland, I checked the EGR valve it was working ok and the temp sensor was reading ok. I received a code of 1255 when I turned the ignition switch on-off-on-off-on, what is this code?

Answer
My wife's Sebring will start and run for about 15 minutes then dies and sound like it is running on only two or three cylinders ( no service engine light). When you let it cool down after 30 minutes or so it will start up like nothing is wrong.She took it to a mechanic he could not find anything wrong, no codes came up. Any ideas?
 
Answer:  Hi Dennis,
I would check the coolant temp sensor to see if its resistance is droping from 7-14,000 ohma when cold, down to about 1,000 ohms when the engine is warm. The other possibility is that the egr valve is sticking open when it warms up. It is located in a pipe from the front manifold that returns toward the throttle body. Its stem is accessible in the flange area between the body and the round vacuum actuator on its top. There is a slot in the stem into which you can insert a screwdriver and move the valve. Make sure that spring-action closes the valve tightly. If not, then spray the stem where it enters the valve body with WD-40 and move it some more.
If you need more advice, use the "thank and rate" tab to get back to me. There is a comments sections to insert your questions/observation.
Try the ignition key to get codes: "on-off-on-off-on and leave on" doing that in 5 seconds or less elapsed time. Then watch the check engine  light to begin to flash, pause, flash, etc. Count the number of flashes before each pause. Then repeat for accuracy. Tell the counts in the order of appearance.
Roland

Hi Dennis,
12 and 55 are the 2-digit codes. Unfortunately they are not diagnostic:
The 12 code means the power to the computer was disconnected sometime in the past 50-100 key cycles, such as disconnecting the battery for example. If that is absolutely not possible then there could be a intermittent disconnect in that battery supply wire to the computer, but it would need to be temp/time dependent which doesn't seem likely.
The code 55 means "end of readout".
I would recommend that you similarly check the resistance of the intake air temp sensor as it, like the coolant sensor, could be "off-value". If either sensor is bad, the mixture could be too rich when the engine is warmed up and produce your problem for that reason.
Let me know the result via the "thank and rate" tab where you can tell me via the "comments" section. Mention the resistance readings when hot, for both sensors, please.
Roland