Engine Code P1176 (AJ-16 Engine)

I am throwing a P1176 code (Lean Condition - Long Term) and a “Check Engine” light in my USA 1995 XJS, with the 4.0 liter AJ16 engine.

I have done the following:

  • Replaced the fuel filter
  • Checked the exhaust manifold for cracks (none)
  • Checked torque on intake manifold (good)
  • Cleared the code, and will be monitoring for reoccurrence

Anyone else ever had this? I understand it can result in poor fuel economy, as the engine ECU tries to “richen-up” the mixture. I’m still getting my normal gas mileage of about 20 (US) MPG.

I may want to pull the plugs and inspect them. Let me know if you have any advice, experience or suggestions.


Check/ clean you Air Flow meter
Check for air leaks after the AFM, smoke test.

And welcome to the forum!

Thanks for the suggestion. I’ll give it a try.

Trying to check everything before buying a set of new injectors…. (Which is one of the recommended suggestion the service documents).

I don’t want to just throw parts at this thing!


When was the last time the oxygen sensors were replaced?

Cleaning out the MAF is a cheap and easy first stab at a solution. Certainly try that first. It should only cost you about 10 minutes and a can of MAF Cleaner spray. Check to make sure the pins on the MAF are making good contact too. You may want to use some electrical cleaner on the contact points at the harness.

As a free check, you may also want to check your ECU connection at the passenger footwell. If there is any green corrosion, that could be the problem as well. Also a cheap and easy diagnosis.

Cats and 4x O2 sensors were changed in July, 2019. That fixed the P420 code it was throwing back then.

I cleaned out the MAF sensor, and checked the intake tract for leaks…. Looks good.

Pulled plug #1, also looks good. Guess I have to drive it a little bit now.

In the next week or so, I’ll try & look at the ECU connections, but it’s pretty dry here in Arizona, most of my electrical connections are in good shape.

Thanks again for the advice.


Pull the little hose at the fuel pressure regulator.

If there’s any moisture or fuel smell, it could be the fuel pressure regulator.

Does anyone know the “theory” of this P1176 code? The info I found on line is not very elucidating.

My guess….

Fuel input (mixture) is derived from the MAF and estimates of the fuel injected by the ECU.

Somehow the ECU estimates mixture richness/leanness via inputs from the exhaust O2 sensor(s), based on what it THOUGHT it was injecting.

That must be how a vacuum leak COULD cause this error… or a “real” lean condition (low fuel pressure - injectors, pump, valve or filter).

I would just like to better understand the problem I’m trying to solve….

Thanks -


And a exhaust leak before the 0² sensors that sucks air (venturi effect).
And add also the PCV valve at the equation.

I recall this document being very useful to learn about how the car is fuelled.

Thank you all for the support.

Very helpful.

Good news. After doing all these checks, and minor cleanups, we have driven about 600 miles, and am not throwing any codes!

So maybe it was the fuel filter, or an O2 sensor connection…

Car is running good, getting about 22 mpg!

Thanks, all!