Looking for some help with my 1996 F350. Details: 460 gas motor, 4EOD, 4x4, 106k. I just pulled the motor to replace the heads due to exhaust port rot. While I had the engine pulled, I removed the smog system. I plugged the ports on the exhaust manifolds and removed the smog pump and hoses and valves. I left the EGR valve in place, got a new EGR hard pipe and fitting that connects it to the exhaust manifold.

The motor runs great with lots of power, no hesitation, no smoke or ticks. The problem I'm running into is that it seems to idle high. I don't have a tach in my truck but I'd guess it's at 1000 to 1100 RPM. Also, I'm getting a few data trouble codes. When I start the truck, there is no CEL. After driving for 5 or 10 minutes, it comes on. I'll turn off the truck and start it again... no CEL.... drive for 10 minutes and it's back on.

KOEO codes:
172 - system lean
173 - system rich
128 - MAP vacuum not changing

KOER code:
172 - system lean

The first thing I thought to check was for a vacuum leak. I sprayed some brake cleaner around the engine but didn't hear any change in idle. I think I need to do this again more thoroughly. When I put the motor back together following the head job, I was very careful to connect everything and check all lines.

I've got the truck up for sale and don't want any potential buyers to be scared off by a check engine light so getting this sorted out is a priority. Any input would be appreciated!

 

Code 128 is a Continuous Memory (CM) only code. Clear the codes then drive the truck again.

Codes 172 & 173 can be displayed in CM or KOER. Since Code 173 is not in the current KOER code list I also suspect it is a code from the past.

Code 172 is the most likely cause of your CEL. Since you have a high idle as well, I suspect a vacuum leak. I have never gotten conclusive results using the spray method to find vacuum leaks on a modern EFI engine. I prefer to use a hand held vacuum pump/gauge to test each circuit.

 

Since you have a code for MAP vacuum not changing, I would start with checking the map sensor and its vacuum source. A bad/incorrect map signal will cause the other two codes.

 

I would tend to agree, but the MAP code is from CM, not KOEO/KOER that is why I suggested to clear the codes, drive the truck for a bit then re-check.