I've got a 2003 Ranger with a 3.0. A week ago I had to make my way through 2-3 feet of mud for work. Made it through just fine, and was in the mud no longer than 5 seconds. I get back onto the highway, and the truck ran fine until I got to a stoplight. I then noticed that it started to idle in the 400rpm range, and jumping back and forth. Decided to replace my IAC which was still under warranty, and that helped the idle out. However next the truck developed a strange bog or hesitation upon acceleration when the truck warms up. I can start the truck in the morning and drive for about 20 minutes and it's fine. But after that period whenever I come to a stop, and then go to accelerate from that stop, the truck kinda moves, but seems to bog down for a second or two, and then kicks in and goes. It seems to do fine driving down the highway, seems to have plenty of power, but i'm not too sure on that. Anybody have any ideas on what to check? There are no codes, not even pending. I'm kinda unsure of what to check first. Thanks for any help and suggestions!

 

Have a look at the air intake all the way to the air box, air filter, & MAF sensor, to see if running through the mud fouled things up inside.

If that looks ok, measure the throttle position sensor resistance, paying close attention to it's resistance reading at closed throttle & when it begins to change when you go from closed to open throttle.

When you replaced the IAC, did you disconnect the battery B- cable while doing it, to wipe the computers KAM & then go through the process of it relearning it's cold & warm idle stratedgy with the new IAC?????

 

The air box did have a small amount of caked up mud that I must have missed, so I removed the entire assembly and cleaned it out. The air filter was a little dusty, but not enough to affect the airflow. The MAF was clean, as was the air intake tube. I've removed the throttle body and cleaned it up, as well as the linkages. The original TPS had a dead spot between 700-1500 rpms, however when I replaced that the condition did not change. Since the problem only happens as the truck warms up, i'm thinking I have a vacuum leak somewhere. It's hard to tell due to the fan noise, but I think I can hear a ssssss coming from around the intake. Since the computer can easily adjust itself when a leak is present, tomorrow I am gonna hook up a vacuum gauge and see what that tells me. And after I replaced the IAC I did in fact erase the KAM and drove it back and forth down the highway, through stop and go, I stopped in a parking lot each day for 4 days and left the truck in drive with my foot on the brake to simulate stopping for traffic lights, and I also ran the shifter through PRND21 and back again.

 

OK, did you test the new TPS after installation, so you know it's good????? Being new doesn't automatically earn it a pass!!!!!

If you have an auto tranny, when you replaced the TPS, did you again remove the battery B- cable to wipe the computers KAM????? Then with the engine cold & all electrical loads off, start it cold, let it idle down some, then slowly shift into All gears, including R, ending in "N" or "P", then without touching or turning anything on, let it fully warm up & slowly go through each gear again, so the computer could relearn it's cold & warm idle routene with the new TPS & IAC & begin to build new fuel trim tables with inputs from the new TPS & IAC?????

The vacuum gauge test is probably a good idea. If you have a propane torch, you could rig an O2 safe sniffer with it unlit, a piece of tubing & sports needle as a probe to pass closely along the intake & listen/watch for an increase in engine idle speed, as it gets a whiff of the propane through a leak.

If you have, or can come by a scantool that'll read PID's, have a look at the short & long term fuel trim numbers, O2 sensor readings, like switching ranges & speeds, along with the MAF sensor output to the computer, it'll be more sensitive to vacuum leaks than your ear or eye in judging engine rpm or fuel trim changes while doing the propane sniff test.

More thoughts for consideratiion, let us know what you find.

 

Thanks for the extra tips! I did erase the KAM again when I replaced the TPS, and went back through the idle and fuel relearn strategy. I've actually done it twice now because I thought at first I hadn't done it correctly.

I am going to hook the vacuum gauge up tomorrow, but one thing I did notice when I was looking for a vacuum line to hook into by the intake was that there is a hose that connects from the upper intake plenum to a little round thing with a **** on top that is attached to the driver's side inner fender. When I touched this hose, the outer covering disintegrated on my fingers, leaving them black. Now, after I got done with the mud I wased the engine off under light water pressure. But could it be possible that this hose is a vacuum hose and that the light pressure still managed to puncture in some spot? Dude to the deterioration it's impossible to spot a crack. Hose is cheap, so tomorrow i'll probably replace it to be sure. I'd be really happy if that fixes it.

Worst comes to worse I do know of a shop full of ex-Ford mechanics that have the software to read fuel trims, but it's a $60 diag, which i'm kinda :/ on paying just to read numbers. So i'm gonna try the vacuum test first to see if I have a vacuum leak for sure, then I will go from there.

I will update once I replace that hose and do the vacuum test. What i'll probably do is do the vacuum test first, then replace the hose, and then re-do the vacuum test and compare the numbers. That should tell me whether or not the hose was the culprit.

 

If the vacuum gauge turns up naught, do a fuel pressure test & if that doesn't show anything, maybe consider pulling & cleaning the MAF sensor after it's cooled off, with a non residual resipe spray cleaner designed for cleaning the MAF sensor.
Be careful not to damage the sensors electrical element & be sure to get & keep it squeeky clean upon re-installation. I know you said your inspection indicated it was clean, but a visual may not be good enough!!!???? These are things you can do before forking over your gold for a pro diagnosis.

More thoughts for consideration, keep us posted on your findings.

 

Thanks for the further suggestions.

I replaced the deteriorating hose today. When I consulted my 02 Wiring Diagram and Component location book from Ford, I see that the hose leads from the intake to the EVAP purge valve. Unfortunately it is close to 95 degrees here in Florida, so I just decided to replace the hose without doing the initial vacuum test to save time in the heat. However after I replaced those I hooked up the vacuum gauge, and the truck is pulling 18 in of Vacuum at about 750 rpms. As I increase the rpms the vacuum gauge needle drops momentarily to zero, then rises back up to 18. Upon deceleration the needle rises to about 23, then drops back down to 18. According to my booklet, the numbers I pulled were within range. However I did this test with the transmission in Park. My truck runs great in park, so i'm thinking of having someone shift into drive while holding the brake, and then re-performing the vacuum test under load.

As for the MAF sensor, I have already cleaned it previously with CRC Mass Airflow Cleaner. It didn't seem dirty, and if it was, it was just dust that was taken care of with the cleaner. I did make sure that nothing came in contact with the thin wires, so I'm pretty sure the MAF is okay in that aspect.

I have still yet to test the TPS again, however I will do that if my Vacuum test under load passes.

I will update my findings later tonight. I really appreciate the help.

 

I went out and tested the new TPS today. As I moved the throttle plate by hand, the voltage moved gradually upwards in what seemed to be large increments. For example, it would go from .80-1.23-1.45-1.90-2.30, etc. Does this mean the TPS is faulty?

 

Are you using a digital multimeter????
For this test, an analog type multimeter is easier to use & interpret than a digital meter.

 

I don't have access to an Analog multimeter, so i'm dead in the water there. I decided to just go back to Autozone and swap the TPS out for a new one. When I compared them both, it sure looked like the one I had was from Ford, while the new one definitely looked aftermarket. I'm wondering if a broken Ford one ended up in the good pile somehow and they sold me a bad one. Either way, the truck seems to be doing better. I haven't erased the Kam yet, but getting ready to go do that now. I'll update in a few days on how the truck is running.

 

You can use a digital multimeter, but you have to go slower & be more steady in opening the throttle, so the resistance changes steadily, but it's more difficult doing it with a digital meter. I still have & use my analog multimeter on many trouble shoots!!!!

 

Yea, that's where my problem was. I went extremely slow yet it still jumped a lot of digits. Upon three tries I just gave up. I wiped the KAM yesterday and helped the truck relearn it's cold and warm idle strategies, and so far it's been okay. Haven't taken it too far yet though. Will update when I know for sure whether or not it is fixed.

 

Well, the truck is still giving me problems.

I'm gonna have a friend come over and i'm gonna have him put the truck in drive while I have the vacuum gauge hooked up, and see if the vacuum reading is iffy when the truck is in gear. If this doesn't show up, i'm kinda suspecting something being up with the transmission, since the idle drops only happen when I put the truck into gear, or when I first start to accelerate. This problem is soo confusing.

I'm thinking maybe something is wrong with the Torque Converter? Maybe it's lockup function is awry?

 

Here is a link to a moving graphic vacuum gauge tutorial, you may find useful.
How to Use and Interpret a Vacuum Gauge

 

That's actually the link i've been referencing.

One related problem i've neglected to mention is whenever I put the truck in reverse when it's warm. If I let the truck coast backwards under it's own power, it's fine. But if I apply the gas in any amount, the truck has a severe shudder to it, almost to the point of dying. The shudder is similar to what happens in drive, but it's much worse in reverse. This problem in reverse has been going on for quite a few months, much longer than the problems i'm having while idling in drive and accelerating. I can't remember when the truck started doing the reverse deal, but it wasn't doing it when I bought the truck in September.

Also, how much of the exhaust should I be feeling from the tailpipe? Whenever I walk by it, it never seems to be pushing out a lot of exhaust, at least not as much as i've felt with other cars. I'm also wondering whether or not my exhaust system may be clogged?