CEL at idle speed?

[Supertrucker]

Hey guys, I've got a 1991 GMC Suburban, 6.2L w/ Banks turbo kit. Lately, it has thrown the light once the engine reaches operating temperature when it is at idle, around 500 rpm on an ISSPRO gauge. I'm still learning about these engines and this is my first diesel so bear with me. It has approximately 183,000 miles and other than the light, seems to run just fine. It gets around 17mpg when recently checked on a 300 mile trip on the interstate with the cruise set at 70mph. The idle doesn't seem to be rough and there's no excessive smoke. I have been adding Power Service to the tank at fill ups, so I was wondering if the ULSD has anything to do with this? The oil pressure shows above 40 pounds on the gauge as well. I recently installed a new alternator and batteries as those were weak. Other than that, I haven't really done much since I bought it. It also only had 600 miles on a full service when I bought it. I have only put on about a 1000 miles since then. Let me know what you think.

[Supertrucker]

Oh...I should add that once the engine speed climbs above idle, the light goes off.

[Robyn]

EGR fault most likely
The 91 did not have much in the way of codes to worry over.
May be the egr solenoids on the Valve cover or possibly a vacuum issue.

1500 or 2500 series??

Pull the codes and we can see whats going on.

I had a 91 and the light would come on every so often and it was anoying but thats about all.

Good luck and good to have ya

Robyn

[Supertrucker]

Thanks for the info. I had a feeling it may have been egr related, but I will check the code and see what happens. It's a 1500 series by the way. I didn't think it was anything serious since the running quality didn't really change. Now, if the problem is egr related, is there some way that I can remove the egr system short of changing the intake manifold to a J code? Another question I had has to do with oil in the bottom of the Banks airbox. I took the filter out to clean it and noticed an oil film inside the airbox and a small puddle in the bottom of the box. I hope this doesn't mean that the seals in the turbo are out or it needs to be rebuilt.