1994 L6 130k --runs great, been insanely reliable for last 10 years.

I am trying to get past smog once again. This time I failed for running too lean. I pulled the plugs and they were pure white verifying the lean condition. Before getting it smogged it was throwing a O2 sensor code like it often does. Replaced it with a Bosch O2 sensor and the code went away like it always does. So back to the lean condition.

I checked for air leaks and did not find any. I replaced the fuel filter and it did not help. One odd thing is that ocassionally the car idles up and down and then starts idling higher and higher --indicative of an airleak though when I unplug the IACV it goes back down to normal and everything is fine no more run away idle or up and down idle. Car idles perfectly at 650 when stopped at lights etc. Its fine until I unplug the battery and then it does the up and down run away idle things. No check engine codes. ...but it fails smog for being lean...

So what exactly controls the air fuel ratio when not at idle. Since the car failed smog at 25mph and 15mph. Is it the O2 sensor that gives the reading that adjusts the injectors? Could I have the wrong O2 sensor? 94 only has one and its downstream... Would the IACV also effect when not at idle? Maybe some sort of internal leak or its sticking?

Lots of questions and Im all over the place here. Basically, trying to solve a lean condition.

 

Hi Hoodun

I've never done this on my Jag but I've done it on my Merc, which 'may or may not help you'

(1) Check the Fuel Pressure
While I know you've changed the Filter it 'Could' (only 'Could'!) be a Failing Fuel Pump (let's hope not)

(2) Check the IACV (Idle air control valve)

Stone Cold Engine: Start the Car and then unplug the IACV (then turn off the engine) do NOT allow the Engine to Warm up!

Remove the IACV and measure the Piston, which will (should) extend on Start Up to allow more Fuel in

Replace the IACV plug it in, then Start the Car only this time let the Engine Warm up

Then with the Engine Still Running (Unplug the IACV) and THEN Switch off the Ignition

The reason you would do that is to Freeze the IAVC Piston in 'Time' which wouldn't happen if you just switched off the engine

Then Remove the IAVC and measure the Piston in the IAVC again, where you 'may' find that the Piston in the IAVC is Stuck

As I say not done this on a Jag but this was the problem on my Merc and I managed to fix it

Maybe the IAVC Piston is Sticking on the way out and not fully extending

 

 

The coolant temp sensor was replaced a couple years back. The TPS was replaced around the same time. I have a multimeter and use it quite often. What are the readings for the MAF. Is there a way to clean the MAF? Car was recently sanded and painted so it could be dirty from dust...

 

The easy answer is to go to your parts store and get a can of MAF Cleaner. Not electrical contact cleaner, but MAF Cleaner. It'll say so on the aerosol can. Then take off the MAF and spray her up and see what happens.

The other option is to have someone press the gas while you take voltage readings at the MAF harness and/or the ECU pins.

I'll have to check my manual to see what the proper readings should be, but in the meantime, go get some MAF Cleaner!

 

Maybe EVAP valve not work properly.

 

Idling high is indicative of a air leak in the sense that its lean, which doesn't have to be from extra air. My 4.2 bent a valve from running lean (I hunted all over for vacuum leaks for he high idle) and it turned out to be poor fuel pressure from clogging.

Would recommend checking fuel pressure as well as getting a vac gauge to help look for leaks.

 

How do I get to the MAF sensor. I pulled the entire piece out and even unscrewed the two screws to pull the sensor but it was stuck in there via wires. I didn't want to pull too hard so I screwed it back... The new ones are only sold as one entire piece so I am thinking its not made to come out, which makes it impossible to clean.