need help with a 4.6 in a crown vic
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MAF = Mass Air Flow sensor. It's the thing in the round housing bolted to the back of the airbox. Remove the sensor CAREFULLY and spray some electrical contact cleaner on the two thin little wires (DO NOT use carb cleaner). You can use a Q-tip to scrub off stubborn deposits if you are VERY, VERY careful about it. However, I doubt this is what's causing your problem, which leads us to...
IAC = Idle Air Control valve. This is on the side of the throttle body at the top of your intake. It's not a major ordeal to remove - just unplug the connector and remove the two bolts - but it's in kind of a pain of a location on the '91 to '95 model 4.6's, because of the different intake elbow and such (points to the front instead of to the side). Remove this thing and hose that sucker out with THROTTLE BODY cleaner - NOT carb cleaner (which can eat up Teflon coatings and such) - and get all of the carbon crap out that you can see. Shake it out and let it dry for awhile before you bolt it back in there. If that doesn't help, you may (or may not) need to invest in a new one, but it's best to try cleaning it first before blowing a wad of cash on a replacement.
HOWEVER...
One annoying thing I've always had an issue with on early 4.6's is that stupid friggin' vacuum line running underneath the throttle body elbow. It's this funky reducer of a fitting that goes from something like a 1/2" nipple by the throttle body down to something like 1/4" hard plastic vacuum line that loops around to the PCV valve on the passenger's side. It's a major pain to see, but if you reach back and under there, you can feel it. I wish I had pics available to show you - check out a diagram of the throttle body elbow area in a Chilton manual and you'll see what I mean.
That vacuum fitting will tend to get all sponge-like and soft as it dry-rots, and it will usually collapse upon itself and/or spring a major vacuum leak. This thing will positively drive you nuts trying to figure out what's causing the problem unless you already know what to look for. I had this problem on my '94 Crown Vic Police Interceptor, my dad had the same on his '92 Crown Vic LX, and I had the same thing again on my '94 Cougar XR7, all with the same 4.6 design. The thing would stall out sometimes right after you stall it, stumble a bit when taking off from a stop, shudder around at cruise on the highway, and sometime trip a Check Engine light.
Two ways to fix it:
1. Buy the whole PCV valve "assembly" from Ford for around $40.
2. Take the old fitting off, go to a parts store, and piece together your own reducer connector with vacuum line and fuel line with a vacuum connector to adapt the two pieces together - might cost you $5 at the most.
One last thing would be to unbolt the throttle body elbow, itself, swing it up out of the way, and scrape out the built-up carbon crap in the EGR passages of the intake (use a Shop Vac to slurp the pieces out that you dislodge, as you don't want them falling down into the intake). This usually won't cause an idle problem, mostly just a steady-cruise stumble, and it'll keep triggering an "EGR valve malfunction" kind of trouble code. It'll cost you about $5 for a new throttle body elbow-to-manifold gasket, and maybe 30 minutes of your time.
Lastly, double-check every piece of vacuum line underhood. There's not a whole lot of 'em on the 4.6, but any one of them can make the thing act all kinds of funky until you remedy the problem.
IAC = Idle Air Control valve. This is on the side of the throttle body at the top of your intake. It's not a major ordeal to remove - just unplug the connector and remove the two bolts - but it's in kind of a pain of a location on the '91 to '95 model 4.6's, because of the different intake elbow and such (points to the front instead of to the side). Remove this thing and hose that sucker out with THROTTLE BODY cleaner - NOT carb cleaner (which can eat up Teflon coatings and such) - and get all of the carbon crap out that you can see. Shake it out and let it dry for awhile before you bolt it back in there. If that doesn't help, you may (or may not) need to invest in a new one, but it's best to try cleaning it first before blowing a wad of cash on a replacement.
HOWEVER...
One annoying thing I've always had an issue with on early 4.6's is that stupid friggin' vacuum line running underneath the throttle body elbow. It's this funky reducer of a fitting that goes from something like a 1/2" nipple by the throttle body down to something like 1/4" hard plastic vacuum line that loops around to the PCV valve on the passenger's side. It's a major pain to see, but if you reach back and under there, you can feel it. I wish I had pics available to show you - check out a diagram of the throttle body elbow area in a Chilton manual and you'll see what I mean.
That vacuum fitting will tend to get all sponge-like and soft as it dry-rots, and it will usually collapse upon itself and/or spring a major vacuum leak. This thing will positively drive you nuts trying to figure out what's causing the problem unless you already know what to look for. I had this problem on my '94 Crown Vic Police Interceptor, my dad had the same on his '92 Crown Vic LX, and I had the same thing again on my '94 Cougar XR7, all with the same 4.6 design. The thing would stall out sometimes right after you stall it, stumble a bit when taking off from a stop, shudder around at cruise on the highway, and sometime trip a Check Engine light.
Two ways to fix it:
1. Buy the whole PCV valve "assembly" from Ford for around $40.
2. Take the old fitting off, go to a parts store, and piece together your own reducer connector with vacuum line and fuel line with a vacuum connector to adapt the two pieces together - might cost you $5 at the most.
One last thing would be to unbolt the throttle body elbow, itself, swing it up out of the way, and scrape out the built-up carbon crap in the EGR passages of the intake (use a Shop Vac to slurp the pieces out that you dislodge, as you don't want them falling down into the intake). This usually won't cause an idle problem, mostly just a steady-cruise stumble, and it'll keep triggering an "EGR valve malfunction" kind of trouble code. It'll cost you about $5 for a new throttle body elbow-to-manifold gasket, and maybe 30 minutes of your time.
Lastly, double-check every piece of vacuum line underhood. There's not a whole lot of 'em on the 4.6, but any one of them can make the thing act all kinds of funky until you remedy the problem.
What year is it? Some older ones had a vacuum 'T' near the upper plenum back by the firewall on the passenger side that would collapse over time, and a hole would form in it. It's also on older Tbird and Cougar 4.6s as well, and every one I have come across has been collapsed. It causes all sorts of weird idle problems, and even some lean conditions.
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