As the subject says I am having a problem with a rough idle and setting code 45. This only happens when the truck is warm, when cold it idles fine. This is an '87 GMC with a 350 tbi.

If, after the truck warms up, I sit at a light the idle gets very rough and throws a code 45. It also feels like it is going to pull away if I don't hold the brakes. I have diacom data which shows the O2 sensor reading (constantly) above 900mv during this time, and of course it goes in to open loop. All other sensors read normally. Immediately after hitting the gas a little (or putting it in neutral) the ses light goes off and it goes back to closed loop. The truck accelerates and runs smoothly, just problematic at idle.

I have tried all of the following (only ac delco parts used):

Replaced EGR valve
Replaced all plug wires
Replaced dis. cap and rotor
Replace all plugs (they looked normal though, nice tan/white)
Replaced O2 sensor (that also looked normal, no carbon build up)
Replaced air filter
Replaced evap. can. filter
Replaced fuel filter
Replaced fuel pressure regulator
Replaced both fuel injectors
Replaced MAP sensor

Fuel pressure is normal
Return line is not clogged
There is no fuel in the evap. can. line
PCV system is working normally
The gas mileage is normal
I triple checked and there are no vacuum leaks
Vacuum at idle is normal, until code is thrown, at which time the vacuum drops (as if under load)

I am thinking that it might be the torque converter engaging at idle and causing the load and ultimately the rich condition, but I really don't want to change it unless I can find out for sure.

Any comments/suggestions would be GREATLY appreciated.

Thanks,
Bill

 

It's not your tq converter. My car seems to idle higher lately than it used to. Try disconnecting the battery for 30sec. or so then see if the fast idle returns. You may also have a plugged up egr passage.

Steve