I've had a problem for some time now, where my 97 2.3 is a dog once the engine warms up in lower RPMs. I've concluded after replacing the following parts: both coils pack, plugs (double platinums autolites), wires, catalytic converter, intake gaskets, fuel pump, air filter, fuel filter, and upstream O2 sensor, as well as testing with a multimeter all of the sensors involved (that i know of) in fuel delivery. Also, my mechanic moved the timing belt one notch forward. He theorized that I had the wrong head, as there are a few that will supposedly work but they have port differences. Further research told me that although he would be correct on earlier years, there was only one 8 plug head manufactured. After I brought this to his attention, he told me that the only thing that it would do is make the engine run leaner. At this time I was still getting a rich code.

Later, on my own accord, I decided to unplug the IAT sensor, as it was the only one I cannot find any specific parameters for to test, and the truck seemed to run fine when in open loop mode (ie cold). This seemed to help, and there is no longer a rich code, but I have an IAT code, and the truck still doesn't seem to run top notch. It still seems to be running slightly rich. Today I decided to short it, and that seemed to help more (in theory it should be telling the PCM that the air is really hot, therefore reducing the fuel delivery.) But, the light is still on, and I also tested the ECT sensor. When cold it should read 40K, mine reads 11K. But hot it should read about 3k. Which mine does. So, I figure it is not playing a role in my problem.

Does anyone know what resitance values the IAT sensor should have when cold and hot. The haynes manual isn't specific. I believe cold I got 25K, and hot I got about 14K. That didn't seem to be a huge fluctuation.

Also, is unplugging the IAT sensor and seeing a performance gain indicative of a bad IAT, or is the PCM just going into open loop mode because there is a code, and my truck just runs better in open loop mode because some other sensor is faulty?

 

Lots of things going on here, but in general, why did you replace the heads mess with the timing belt & all those other things, were they efforts to address the "power" problem?????

Post ALL the trouble code numbes you have & the order in which they were retrieved.

The IAT resistance is higher, when it's cold, @68F it's resistance is approx 275K ohms & lower when it's warm, @ 160F about 7K ohms.

If the ECT resistance is that far off when cold, I'd replace it, as it could confuse the computer about true engine temp & when to switch between open & closed loop.

When the engine is running in open loop, it's A/F ratio will be richer.

 

Well, I didn't actually replace the heads. My mechanic said that the truck looked like it had recently had head work done to it. I've only owned it for about 4 months. He advanced the timing because at the time we were getting a rich code, and after testing all the sensors, he couldn't find any problems. He discerned that it must have been the incorrect head that was placed on the truck when the work had been done. After searching, I found that there was only one head manufactured that had 8 plugs. But there were two heads that had four plugs. But, mine is the eight plug type.

The only trouble code I have now is that the IAT sensor is unplugged. If I plug it in a drive around it goes away and the check engine light goes off. As far as I can tell though, the engine appears to perform worse. There is a noticeable lag in the throttle from a dead stop. This appears to clear up some when I unplug the IAT. I still don't think it is perfect either way though.

I'm sorry but I have forgotten the old codes, i think it was P0104 if I remember correctly.

 

OK, I see, it's the 97 Ranger 2.3L with >300K miles on it.
So to know it has that kind of mileage on it, you must know the previous owner/s, so maybe they could shed some light on it's past maintenance.

How does the IAT's resistance measure up to the above temp/resistance numbers I posted????

If you replace either of those two sensors, or clean the MAF sensor, be sure to pull the computers power while your working on the sensors, to reset the computer, so it can relearn it's fuel trim.

The P0104 code you posted is for the MAF sensor. So have you checked, or cleaned it???? A dirty MAF will be slow to respond to changing air flow & thus cause the computer to be behind the power curve with fuel trim.
If you've cleaned the MAF sensor, or replaced it, or any of the other sensors & not reset the computer, it'll be working off it's old learned fuel trim numbers & not run well for a while, until it relearns.

If you find the MAF is dirty, you need to look up stream & find out why it got dirty.

Just a couple more thoughts for pondering.

Let us know how it goes.

 

Well, I did clean the MAF, again I'm not sure if that was the correct code, I was trying to remember off hand. I also tested it with a multimeter and the voltage does increase and decrease relative to throttle position as it should.... I suppose as you say, it may be doing it slower than it should, and that would be hard to tell. I've also tested the TPS sensor and it seems to fluctuate at the correct levels as well.

the measurements I got for the IAT sensor, were at about 85 degrees 25k and at probably a 120-130 range 14k. I tested it both in the air box, and out, holding a match under it to apply some heat.

 

I forgot to ask if you've verified that the IAT has it's 5 volt reference.

If it doesn't, or if this reference voltage is higher, or lower, the out of tolerance signal return voltage, from the IAT to the computer, will confuse the computer about the true inlet air temp.

Since cleaning the MAF, have you reset the computer, so it can relearn it's fuel trim????

Edit: I just got your PM & the computer screwed up my answer, so I'll just do it here.

With the truck running ok sometimes, I agree with your Tech, that the probem isn't likely a mechancal engine one, but maybe a border line, or out of tolerance sensor.

SO, I'd recheck or replace that ECT sensor, as it's cold resistance readings you posted, look to be too high.

I'd also try to do a more accurate IAT temp/resistance check, as the numbers you posted don't look just right, with the test temp.

Also with the low mpg, driveability problems & mileage on the vehicle, I'd have the O2 sensor/s switching speed checked out.

If they are lazy & slow to respond, the computer will be behind the fuel trim power curve.

 

Well the upstream O2 sensor is new, as I understand it the downstream doesn't affect fuel trim, it just tells the comp whether there's a Catalytic converter or not. I replaced the ECT and the IAT, funny thing is, after about two months I got a p0113 code on the IAT, so I had to put the old one back on. It now went away. Kinda weird the new one would go bad so soon. The truck runs a lot better now, but when it's warm outside it still has trouble from low speeds accelerating. I noticed today when it was about 50 degrees outside that the truck runs absolutely perfectly. Do you think that although the readings I'm getting from the MAF sensor appear to be correct that I just should change it? I can't figure out why the fuel trim would be incorrect during the warm days, and good on cold days, unless something is wrong with the fuel/air ratio. I'm going to try resetting the computer and cleaning the MAF again tomorrow to see if this clears anything up. It's been so long now, I can't remember if I reset the computer. Any other ideas?

 

I like those last two ideas.

Use a spray that says it's recipe is for cleaning MAF sensors & remove the MAF sensor for cleaning, so you can get to it from all angles & so the spray & anything it removes doesnt get ingested by the engine.

Sounds like your on the right track. Will be interesting to hear if resetting the computer will finally put things right.

Any time we make a repair to the emission control system, we are to reset the compuer, so it can relearn new parameters caused by the new parts.

As a system ages, the computer adjusts things, up to it's preprogrammed limits, if we then come along & change something & don't tell the computer (reset it) it'll take it a while to wake up & begin to reset things.
If it's at it's extreem limits of change, it'll take longer to relearn & we might think we didn't fix the problem.

So if you didn't reset the computer after replacing the IAT, how was it to know you replaced the IAT????

How did the IAT 5 volt reference voltage check out & how did the O2 sensors switching speed check out????

Just some more thoughts & questions to ponder.

 

Some more thoughts after re-reading your previous posts.

Lets see, you say you've replaced the O2, ECT & IAT sensors, but didn't reset the computer after the sensor repacements.

Then removed the new IAT sensor & tested it's resistance while holding a match to it & now think it's bad, or questionabe, because the engine didn't run better, but remember, you had not reset the computer after the new IAT, ECT & O2 sensors were installed, so how was it to know you had done the repairs, you didn't tell it, by resetting it's memory????

So now you've removed the new IAT & reinstalled the old one, that you know isn't in spec & are now going to reset the computer & hope it runs better????

That poor old computer is going to be so confused it won't know whether to poop or go blind. lol

If the new IAT's resistance range is still ok, ie, heating it with a match didn't ruin it, I'd re-install it, or get another new one, so you have a known good IAT, ECT & O2 sensor, then if you want too, reclean the MAF with a MAF cleaner, THEN reset the computer & let us know how it goes.

If you have a auto tranny, after resetting the computer, start the engine cold & let it idle down some, then slowly shift into ALL gears, including reverse, remaining in each gear long enough to feel it engage, before shifting into the next one, then don't touch the throttle & let it idle until it completely warms up & then slowly shift into ALL gears again. This way it'll learn it's idle speed & fuel trim quickly & the remainder it needs to learn can be done during upcomming drive cycles.

Then let us know how it's doing.

 

well i recleaned the MAF today and reset the computer. I used some terminal cleaner this time, which may not have been a good idea but I figured it was better than carb cleaner, except when the particulate runs through the intake it causes the truck to sputter for a while. Anyways, I was off and running good for about 6 miles afterward and then the truck began to surge, I pulled over and unplugged the MAF and replugged it back in and the surge went away, but I still have crappy power. I tested the voltage at idle and it is around .9V: toward the middle of the accepted range.
The truck appears to be very sensitive when fooling around down there though. If the truck is running and I just remove that rubber "stopper" around the wires that run into the MAF in the cleaner box, the RPM's suddenly pick up. That's a rather small volume of air to make such a drastic difference. I'm leaning toward the fact that this MAF maybe within spec per se, but considering the ambient conditions may be a little off, because it is still in the 70s to 80s, so the voltage I would imagine should be on the low end, as the volume of air at that temperature should be rather low, am I incorrect in thinking this? After the truck is moving, there is really no issue with its running condition, it is below 5 mph that it seems sluggish. As I said before in colder themps this condition goes away, and even seems to be absent for the first 30 seconds of a cold startup. Also, the truck runs much better without the AC on, it seems this load really affects performance. I suppose it is just magnifying whatever the problem is. I believe it is running rich based on the smell of the exhaust. It smells rather gaseous. No white smoke though.

 

a rich engine will always run smoother in cold weather. Hot weather density is no good, rich or lean. As far as fuel trims go guys.. pulling the battery wire isn't doing any good for anything let alone it kills all your emissions monitors. Once you erase those fuel trims you have to run a manufacturer specified drive cycle to relearn trims. Basically, if you fix a problem it will show up on short term fuel trims, and correct long term fuel trims accordingly. so it will indeed learn the fixed problem without trashing all of your hard earned live memory.

 

I actually replaced the MAF and it fixed the problem. I guess although the voltages seemed right, it must have been slow on the uptake or something. Thanks for all the help!

 

OK good feedback & to hear you finally got it put right.

The fact the truck seemed to run ok for a bit, then act up again, may have been due to the product you chose to clean the MAF sensor with.

If the "terminal cleaner" you used, had any "contact lube", or other "residual" products in it, that would coat the MAF sensors hot wires after it evaporated, it could bake on the MAF's heated wire & mess up the MAF's air flow sensing calibration.
It would tend to be slow to respond to small air flow changes.

Thats why I was suggesting removing the MAF to be able to get to it from all angles for cleaning & using a "non residual" spray cleaner, that says it's properly formulated for cleaning them.

BTW have you done any air intake mods, or changed the OEM paper filter out for a oiled foam, or cotton gauze type air filter????

If so, don't be surprised if this happens again, as those filters don't filter down to as small a partical size & if you over oil, or use the wrong oil on the filtering element, it can contaminate the MAF sensor !!!!

Just some additional thoughts for pondering.

 

i did actually modify the intake box some, i cut an opening in the top to make it function like a cold air intake, as the shape of the filter and all is the same. I did this after the problem because I thought it was related to air flow, as I would see such drastic differences in idle just by allowing small amounts of air into the inlet tube by moving the rubber stopper behind the MAF. I suppose I should see if I can find the OEM part at a junk yard and put it back in, but I'm busy doing a timing belt right now, because way back when my mechanic advanced the timing to compensate for the crappy driving quality as he could not find the problem either, and i think he had a pretty competant scanning utility. He chalked it up to the possibility of a wrong head, as he said the head looked recently done. I later found out there was only one 8 plug head manufactured.