So my 99 ranger 6-cylinder 4.0 OHV has had the CEL on for these codes for months. I have tried replacing the MAF the o2 sensor the IAC valve to no avail. But just recently the truck has gained an even rougher idle then before. It acts like it is trying its hardest to stay running while idling and occasionally just die. There has been a few days where it would die with me while driving as soon as I let off the gas. So here i am wondering what else this could be, low fuel pressure from a pump that's on it way out the door or an upper/lower intake manifold gasket? I have also checked the PVC valve and all the hoses with no luck. I am debating on getting the truck looked at by a local garage to help me pin point the problem before i invest money and time into doing either the fuel pump or the intake manifold gaskets myself to find out that it did nothing at all. Any light or similar experiences that anyone can share would be greatly appreciated! Thanks.

It is your lower intake gaskets are bad and need to replace them that is what fixed mine

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1999 Ranger 4.0 and extreme Snap-on tool fetish

http://www.therangerstation.com/foru...ad.php?t=94437

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1998 Ranger XLT Super Cab 4.0 ohv v6 - 5r55E automatic Trans - 8.8 with 3.55gears - Toreador Red Clear Coat Metallic -Explorer Sport Trac White Faced Gage Cluster -2006 Mirror Swap-16" Mustang wheels with 215-65-16" Falken Tires

I had the code for lean mixture on bank 1. It ended up being a vacuum leak. When the engine was running I could barely hear a whistling like noise and that was the leak. I put a new hose on and that was the end of that. I've read that those vacuum leaks can be really hard to detect so maybe having a shop search for a leak could be a good start? I'm sure there are ways to do it yourself too.

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2003 v6 4.0 4x4 xlt extended cab
manual transmission 135000 miles
29x12x16 tires bilstein 5100 shocks

Get some starting fluid, start the truck, spray under manifold. If rpm's go up, you've found the leak. Most likely upper/lower intake gaskets.

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1998 Ranger Supercab 4.0L, Medium Metallic XLT, auto, painted valve covers (10 HP), 30x9.5/15.

2008 Mustang GT, stroked 5.0 3v, RGR cams, R2300 S/C, suspension, Kooks LTs w/HF cats GT500 TB, Flowmaster cat-back exhaust, GT500 fuel pump setup.