Intermittent Check Engine Light

So, while driving my '92 Mondial T, after a few minutes of driving, I had the yellow "Check Engine Light 1/4" come on intermittently. It did so again this morning. The interesting thing is that I noticed today, that it would do so only when the vehicle was stopped at idle-- as in when I came to a stop at a traffic light. After being stopped for some 10 seconds, the light would go on. Immediately when I accelerated from a stop because the traffic light turned green, the CEL would disappear. The "slow down" lights never came on. After this happened this morning, I parked the car for about an hour, and when I drove it an hour later, no lights ever came on. I understand that, generally, the CEL is an indicator of catalytic converter temperature, and if the light persists, it usually requires an new CAT ECU (I had the other bank's CAT ECU replaced several months ago after the CEL and slow down lights came on and remained on causing that bank to shut down). However, with this being only an intermittent problem that seems to occur invariably only when stopped at idle, I wonder if there are any other ideas about what this could be-- O2 sensor ?, mass air flow sensor ?, or just a sporadic electrical gremlin.

Any thoughts appreciated. Thanks.

 

Dave:

Thanks. I was under the wrong impression that the CEL, like the slow down light, also related to the CAT temperature but it's good to know that I was wrong. I looked through the 348 linked thread re: pulling codes, and will do that this week to see what I get.

Thanks for the info.

 

So I followed Dave's very helpful advice that linked to the procedure to pull the ECU codes, and did that. There were 3 stored codes:

2111- this is listed in the linked page as an "undocumented code" but appears to be related to the intake air compensation solenoid valve-- which is known to cause a wind whistling type sound between 3,000 to 5,000 rpms. does not appear to be a big deal.

4114-this code corresponds to the TDC control unit. my suspicion is that because my CEL is only coming on when the car is at idle for about 30 seconds or more, and then disappears as soon as the car is in motion, and that it does this even when the car is not hot, that this is the true culprit of the CEL coming on when it does. It could be either a bad TDC rpm sensor unit itself, or a loose connection.

4121-the dreaded catalyzer temp ECU. I replaced a CAT ECU a couple of months ago because I had this issue before (with the slow down lights staying on), and ended up switching the CAT ECU's to opposing sides, putting a whole new unit one on one side, and switching the other one (which did not malfunction) to the other side. This code may be a relic from a couple of months ago when this was done (I am hoping). Because I am not getting the "Slow down" light coming on along with the CEL, and because the CEL comes on at idle even when the vehicle is not at hot temperature, I am optimistically hoping that it is not a CAT ECU issue for real.

Any thoughts ?

I cleared all the codes from the ECU after pulling them, so I will see if the CEL continues to come on, and if it does, I will recheck to see if all of the same codes are still present. The thing is, the car runs and performs perfectly. The only issue is that the CEL 1-4 comes on at idle whenever the car is stopped at a light for about 20-30 seconds or more. I just want to make sure that I am not overlooking something that could lead to a more major issue if not taken care of now.

Thanks again to Dave for the helpful link on pulling the codes.

 

Getting the Kia rpm sensor may be the possible next step. The funny thing is that after I cleared the codes and posted here about it, I took the car for a 20+ mile drive, and the CEL came on during idle only once at the beginning of the drive. After that, despite the fact that I was stopped at a number of lights--a situation that previously would have brought on the CEL without fail-- the CEL did not come on anymore. I am guessing (hoping) that clearing the ECU codes may have solved some of the reasons for it coming on in the first place. We'll see how she does over the next few days.

Thanks again.