My 2002 Ranger XLT Supercab 3.0L manual developed what I call an intermittent idle "hang". I've owned the truck since new, put 135k miles on it, and have done nearly all the maintenance on it myself, using Motorcraft, Ford, or OEM quality parts. I'll see if I can describe what it does a little better.
When I mash the clutch in to shift gears, the engine will hang at the RPM it was at when I let the clutch out (or even flare up 2-300 RPM), and then slowly return to around 1100RPM. Sometimes, it can take up to 10 seconds to start coming down. Here's the real screwy part. If I leave the A/C off, it works perfectly, every time. If the A/C is on, then about 80% of the time, it will hang to some extent.
Now, keep in mind, I've owned this truck since it was new off the lot. I know about the slightly increased idle speed till it comes to a stop, and the rev matching strategy for shifting. Up until about 8 months ago, it worked perfectly. Then one day, it decided to try and kill me on the way to school. Driving a stick, you get used to having engine braking while driving. One day, it suddenly wasn't there.
Rather than tell a long, drawn out story, I'll start with what I've replaced and checked recently, and in the order it was done.
Replaced TPS Sensor
Replaced IAC
Cleaned MAF
Replaced various sections of rubber vacuum line
Replaced PCV Valve, connector hose and valve cover grommet (rotting rubber)
Changed Plugs (they had 60K miles on them)
Replaced Both Upstream O2 sensors (130K miles, it was time)
Cleaned Throttle Body (with a teflon safe cleaner)
Gone hunting for vacuum leaks with carb cleaner (didn't find any)
I've also plugged the truck into my laptop, and monitored live engine data to see if I'm missing something. Fuel trims look good. STFT for both banks sits around 0% to -1%, LTFT is at -2% to -3%. TPS Voltage is .98V closed throttle. PCM picks up on CT, PT and WOT as expected. IAC Duty Cycle goes from about 20% at idle with no accessories on to 40% at idle with the A/C on, to 100% at WOT. ECT and IAT are within 10 degress of each other at cold start. VSS sensor seems to agree with the speedometer. The ONLY things I've found that look a little out of whack are the manifold vacuum, and the MAF voltage. Manifold vacuum drops drastically from around 19.0" at idle to 15.0" when the A/C compressor is kicked on. The MAF voltage tends to fluctuate by about +/- .04V, back and forth at various loads.
I'm pretty much at a loss. The only thing I can think of is a vacuum leak at the plenum (its plastic) where it bolts to the lower manifold, or the lower manifold where it bolts to the heads. And it only wants to show up under load, and when decelerating. The only reason I'm leaning towards that, is about 18 months ago, the coil pack cracked, and I had a pretty good backfire before I found it.
Thoughts, opinions, or suggestions?
When I mash the clutch in to shift gears, the engine will hang at the RPM it was at when I let the clutch out (or even flare up 2-300 RPM), and then slowly return to around 1100RPM. Sometimes, it can take up to 10 seconds to start coming down. Here's the real screwy part. If I leave the A/C off, it works perfectly, every time. If the A/C is on, then about 80% of the time, it will hang to some extent.
Now, keep in mind, I've owned this truck since it was new off the lot. I know about the slightly increased idle speed till it comes to a stop, and the rev matching strategy for shifting. Up until about 8 months ago, it worked perfectly. Then one day, it decided to try and kill me on the way to school. Driving a stick, you get used to having engine braking while driving. One day, it suddenly wasn't there.
Rather than tell a long, drawn out story, I'll start with what I've replaced and checked recently, and in the order it was done.
Replaced TPS Sensor
Replaced IAC
Cleaned MAF
Replaced various sections of rubber vacuum line
Replaced PCV Valve, connector hose and valve cover grommet (rotting rubber)
Changed Plugs (they had 60K miles on them)
Replaced Both Upstream O2 sensors (130K miles, it was time)
Cleaned Throttle Body (with a teflon safe cleaner)
Gone hunting for vacuum leaks with carb cleaner (didn't find any)
I've also plugged the truck into my laptop, and monitored live engine data to see if I'm missing something. Fuel trims look good. STFT for both banks sits around 0% to -1%, LTFT is at -2% to -3%. TPS Voltage is .98V closed throttle. PCM picks up on CT, PT and WOT as expected. IAC Duty Cycle goes from about 20% at idle with no accessories on to 40% at idle with the A/C on, to 100% at WOT. ECT and IAT are within 10 degress of each other at cold start. VSS sensor seems to agree with the speedometer. The ONLY things I've found that look a little out of whack are the manifold vacuum, and the MAF voltage. Manifold vacuum drops drastically from around 19.0" at idle to 15.0" when the A/C compressor is kicked on. The MAF voltage tends to fluctuate by about +/- .04V, back and forth at various loads.
I'm pretty much at a loss. The only thing I can think of is a vacuum leak at the plenum (its plastic) where it bolts to the lower manifold, or the lower manifold where it bolts to the heads. And it only wants to show up under load, and when decelerating. The only reason I'm leaning towards that, is about 18 months ago, the coil pack cracked, and I had a pretty good backfire before I found it.
Thoughts, opinions, or suggestions?
