4.0 OHV identifying california emissions and advice on high idle/lean codes

[SenorNoob]

I get 98-11 when I look up an 02 radiator. Shape is different AND significantly larger. If possible it's be entirely custom work.

 

[Michael Rogge]

I replaced every intake gasket (MAHLE) with torque specs according to the Haynes manual and little changed, engine is a little smoother when it's starting to lug but still atrocious fuel consumption, still have 172 176 411 codes. triple checked every vacuum line and now when I pull one off the manifold the RPM drops (before it increased). Tested plugging each vacuum line except for the fuel pressure regulator and none of them affect the idle. I am now wondering if my idle is actually high, the tach reads 1200 but the tach is also broken (wont read above 1500 when interior cold, stuck exactly on 2200 when interior warm). There is definitely substantial rev hang, it will go up to what sounds like 2500ish rpm while changing gears and when sitting at a stoplight but goes back to the typical idle when the throttle is stabbed sharply. (it has always done this). what's weird is that the throttle plate itself is not sticking, I opened the hood while the idle was stuck high and the plate was bottomed out on its stop screw. unplugging the IAC does not lower the idle either, whether it is idling high or how it usually does. This truck is turning into quite the enigma. my current plan is to make sure the exhaust manifolds are sealed (I hear a tick from bank 2) and replace the 02 sensors (yes I know its a joke about "mechanics" just throwing 02 sensors at the codes). What else could be happening? When I got the truck it had a MAF code which went away when I cleaned it (truck was run with a hole in the intake pipe by previous owner).

sorry for restarting old thread

 

[SenorNoob]

Those 3 codes scream vacuum leak. What they are saying is that PCM has added all of the fuel it can and still getting a lean reading at the O2 sensor.

172	(R,M) Oxygen sensor not switching – system is or was lean – Single, Right or Rear HO2S – Fuel control

176	(M) Oxygen sensor not switching – system is or was lean Left or Front HO2S – Fuel control

411	(R) Idle speed system not controlling idle properly (generally idle too high) – ISC

There are more codes that I would've expected in that situation but OBD1 doesn't usually throw all the codes. I suspect that only certain ones are even enabled on certain PCMs.

I did just notice that it's actually both banks. That's significant. Either too much air or not enough fuel. Not enough fuel tends to cause hanging idle on small engines. No idea if that same principle applies to the 4.0 with fuel injection.

 

[Michael Rogge]

Those 3 codes scream vacuum leak. What they are saying is that PCM has added all of the fuel it can and still getting a lean reading at the O2 sensor.

172	(R,M) Oxygen sensor not switching – system is or was lean – Single, Right or Rear HO2S – Fuel control

176	(M) Oxygen sensor not switching – system is or was lean Left or Front HO2S – Fuel control

411	(R) Idle speed system not controlling idle properly (generally idle too high) – ISC

There are more codes that I would've expected in that situation but OBD1 doesn't usually throw all the codes. I suspect that only certain ones are even enabled on certain PCMs.

That's the theory that I was going with, hence the gaskets. I am replacing 02 sensors and checking for exhaust leaks because it smells rich (though that may have been gas from the filler neck that I just found out is broken) and as far as I know lean AFR won't cause poor fuel economy. Is there anywhere other than that cluster of vacuum lines on the back right of the upper intake or the gaskets that could cause a vacuum leak?