Ongoing 171 & 174 on 99 windstar

Hi everyone. I'm hoping I can get some advice. I can't seem to get rid of the lean codes. So far I have done the TSB for the isolator bolts. The kit included new valve cover, pcv valve and hose, regulator vacuum hose, the new bolts and new gaskets. After I did the repair the codes came back. Further research led me to believe lower intake gaskets were possibly bad so I replaced those. They were definitely bad, letting coolant into the intake but I don't think that was the main source for the leak because codes came back. While changing intake gaskets I also changed plugs, thermostat, and coolant temp sensor. Plug wires were changed about a year ago. None of this seemed to help because code will always come back. I saw the thread about the code reader and forscan so I bought one from ebay and downloaded the software. I don't know enough to properly use the data it provides but do know that high fuel trims indicate lean and low trims indicate rich. While messing around with the pid data I have learned that fuel trims are extremely high. So I started squirting carb cleaner around and from what I can tell the plenum is leaking at the lower intake manifold and the imrc is leaking where the shaft goes in to the intake manifold. When I did the isolator bolts I torqued them to 95 in lbs even though the specs were 89. I wanted to make sure it was sealed. So should I tighten the bolts even more to try and eliminate the leaking and is there a way to seal the shafts of the imrc. Sorry for the long post but hoping I can get rid of the cel once and for all.

Over torqueing the bolts will achieve nothing ... and may lead to their early failure. It may be that the vacuum leak is elsewhere ... use some thick high temperature grease, or an RTV sealer, on all hose connections to the intake ... also on the PCV connections. Some old vacuum hoses may have lost their "character" ... and be leaky, or too swollen to ever effect a good connection-seal.

Also use some grease to seal the IMRC shafts...

The front engine cover may have to removed and the gasket, and shaft seals, replaced ... as it is part of the evacuated crankcase.

Thanks for the reply! I sprayed carb cleaner around all vacuum hoses and where they connect to the intake while watching the live pid's in the scanner. I didn't get any changes when spraying around the vacuum lines. I did however get drastic changes in short term fuel trims when I sprayed around the imrc shafts and base of plenum. I also forgot to mention that I did a poor mans smoke test and was getting smoke coming out of the top of the iac from something that looks like a cap and a little from what looked like the egr diaphragm.

yep, fix those leaks and I"ll bet your code is also fixed.

That is a vent cap on the EGR valve, I believe.

I guess I will pull the plenum again but I don't know if that will achieve anything. I used a torque wrench on the bolts so I know they were tight enough. I even went a little tighter hoping for a better seal. I wonder if the lower intake might be warped or something. Also I have been looking at how to replace the seals on the irmc shafts with no luck. Any suggestions are appreciated.

An artist brush and some hi-temp grease around the shaft (I thought I covered this?) ... it that's not enough for you, follow the grease with several wraps of heavy package twine (cotton fiber) ... you can make it pretty much air tight if you wish. Even felt/fabric washers ... split to go over the shaft ... "stagger stacked"... etc, etc..

I'm not sure there are any real "seals" around those shafts ... I don't think so ... maybe bushings of some sort. I've never done anything to mine other than a few drops of engine oil every 10 years or so. ('bout to do it the second time a few years from now.)