Check Engine light and temp gauge question

[Niels]

Hi all. I have a '99 SOHC XLT all stock. Last week the temp gauge dropped down to the "C" while driving. There was plenty of heat, but the radiator cap was cool to the touch. The wife brought it to the mechanic because of this and the Check Engine light was on.

The mechanic put the code reader on but no codes were logged, according to him. He revved the engine a couple of times and then the CEL went out. Well, now it is back on and stays on. Good heat, all the gauges are working correctly and nothing odd has been noted with the performance of the engine. Everything seems normal.

Given the fact that the CEL is on I tried to find some place open today to pull the code, should there be one. Nothing open on Saturday, of course. The code reader that I borrowed does not have the EEC-V connector. Is is possible to pull codes using the ignition switch like on the Chrysler vehicles or is a code reader the only way?

Also, and I know this borders on a vague/stupid question , what could cause the temp gauge to drop and the CEL to come on? I did look at the temp sensor connection and all of the rest (air cleaner, oil pressure, various vacuum lines, etc.) but I couldn't find anything out of place or obviously wrong. Thanks for any insight or thoughts.

 

[swetrid]

Could be a sticky thermostat, what was the code?

 

[Niels]

I don't have one. My code reader does not have the correct end and the mechanic's in town are all closed today.

 

[Niels]

I brought the truck to the mechanic. He pulled the codes, no numbers but he said that one was for the "Left bank-lean" and the other was "Right bank-lean", or something to that effect. He thought that it probably was the result of bad fuel. He cleared the codes and they stayed away for about week or so.

The CEL is back on and now the first start of the day the engine stumbles and the rpms drop when the engine first starts. Sometimes it'll recover by itself. Other times it dies and needs to be restarted.

Once the engine has been ran for a while it starts fine. The air cleaner was past due for replacement so that was replaced. According to the wife it now starts better, no stumble at any rate.

So, I am questioning if a clogged air filter could cause a lean condition and the stumble on start up. I realize that just because the air cleaner looks good doesn't mean it isn't plugged. On the other hand you would think that a clogged air filter would cause problems across the engine rpm range, not just on start up.

I was thinking that the stumble and CEL were related issues, possibly fuel pump or filter related. Now I am not so sure. Another question is if the CEL will go off with out being cleared by a code reader? Thanks for your help.