TPS/MAF/IAC and the CEL that wont go away

[ap1000]

TPS/MAF/IAC and the CEL that wont go away (o2 sensors?)

Great forum. I have done several searches and gotten loads of useful info, however I am now at a loss.

Two weeks ago, my truck would stall after cranking. It stalled one day and we left it at my wifes office. Below is a brief history of what happened:

1. (friday) mechanic went out and changed fuel filter. truck cranked for him.
2. (saturday) went to pick up truck and it didn't crank. I left it there.
3. (sunday am) came back next day changed TPS, Cleaned IAC Valve. Truck cranked. died in parking lot but cranked right back up and I drove it to mechanics house and had tune up done. (changed wires, plugs, oil, oil filter, degreased engine)
4. (sunday pm) picked up truck. truck began to stall on and off and CEL light came on. mechanic suggested it was O2 sensor b/c he thought it "smelled rich"
5. (monday) truck stalls after being cranked quite frequently. also low idle. always cranks back up. go to autopzone and have it tested and get code P1121 (TPS inconsistent with MAF)
6. drive it a week and it still has low idle and intermittantly dies. also it seem that the throttle has a lag between I depress pedal and engine accelerates. the engine does not respond at all when I "punch it" it just accelerates.
7. (wednesday) replace the MAF. reset the brain of truck. CEL comes back on halfway home. I go to Autozone and it gives me the same P1121. I think about driving into the nearest telephone pole :fire:
8 (thursday) research this forum a lot and determine my IAC must be bad or my TPS isn't seated right.
9. (friday) reinstall my TPS and replace IAC Valve. Reset brain. Drive awhile and CEL comes back on. adjust idle screw to idle the truck a little higher (700-900 rpm).
10. (saturday) truck doesn't idle low anymore, or seem to die intermittantly. CEL omes back on. throttle still seems to have the "lag" I mentioned in #6.
11. (saturday pm) type this post.

Overall the truck seems to be driving well except for this nagging CEL that doesn;t want to die. I am at a total loss. I cant keep throwing money at the truck without having some idea of what is wrong. If you have any ideas, please let me know because it is driving me nuts.

Thanks in advance.

AP
=========
2000 XLT
V6 SOHC

 

[BrooklynBay]

Welcome to this forum! Tracking down intermittent problems could be one of the most frustrating problems, since the problem doesn't exist all of the time. This code P1121 Throttle Position Sensor Inconsistent with Mass Air Flow Sensor seems like the sensor inputs don't match properly to perform the correct A/F ratio. It only occurs at certain times. Were these parts replaced with the same part numbers as the old parts? Does this CEL only pop up at a certain speed, and temperature? Did you clean out the throttle body intake area? As for the delayed response, do you have the throttle by wire set up?

 

[ap1000]

inconsistant problems

Thanks. I'm glad I found this forum.

I replaced all the parts with what I bought from the autoparts store. From what you ay, it seems like replacement parts might be a mixed bag and getting them to "sync up" and get the A/F right could be difficult.

The CEL doesn't seem to happen at a certain speed, but the outside air tempature has been hot lately.

I haven't cleaned out the throttle body, mainly because I didn't know to do that. Is that the area under the IAC Valve and can I clean it with carb cleaner? I will research that and do it tomorrow.

I am not sure what the throttel by wire is, although I am thinking it is the cable that controls the throttle of the engine. It seemed kinda loose to me when I was adjusting the throttle screw, but my eye is rather untrained so I didn't want to mess wit it. Do I need to tighten it and if so, is there a way to do that? I'll look into it. I wonder if a loose throttle cable could cause the TPS to malfunction and trip the CEL...

I'm going to keep on trying until it goes away.

 

[BrooklynBay]

The throttle by wire is an electronic set up which uses the computer to control the throttle. It doesn't use a cable. If you have a cable, then you don't have this. Compare the original part numbers with the new parts. I've had parts counter guys look in their book, then pull out the wrong part. I told them to double check the number, then they said that there were 2 part numbers, and they pulled out the wrong one. Don't use carburetor cleaner to spray out a fuel injected throttle body. Only use one which has a label saying "for use on EFI vehicles). They are O2 sensor safe.

 

[ap1000]

I will clean it out today, reset the brain and let you know how it goes. I'm going to double check the part nos. as well and I hope they match. I dont think I can return them after they've been installed.

 

[BrooklynBay]

Some places like AutoZone give you at least 30 days to return them. If it's more than that, you could explain that they gave you the wrong part, and it's not your fault that you have to return it for the correct one.

 

[ap1000]

I got it retested today and got the same code: P1121. I was speaking to a tech who indicated it could possibly be a voltage inconsistancy. Now I need to find a voltage meter and test it. Does that sound right? Any ideas on what the voltage oughta be?

 

[ap1000]

Today I took the X for a little road trip and was satisfied with its performance. It still has that wierd accelerator "catch up" thing going on (that has much written about it elsewhere) but the CEL stayed on. So when I got home I did the following:

1. exchanged the TPS at Autozone for a new one and installed it
2. cleaned the wire clips to the TPS and MAF with elec parts cleaner
3. replaced the air filter
4. cleaned the throttle body (definitely needed it)
5. reseated and tighten the air intake hose
6. disconnected negative terminal to reset brain and clear code

All in all about 20 minutes of work. When I put her back together, she cranked right up and sounds good. I noticed that it was idling a little high; about 1100 rpms with no a/c on. So, I readjusted the throttle screw (basically undid what I did a couple of days ago) to get it about 900 rpms.

My son and I took a ride around for a while and no CEL light. Maybe I got it. Maybe not. I'll post in a day or so and update.

Also, for what it is worth it seems like the accelerator is behaving a bit better as well. I hope that it is just not wishful thinking.

AP

 

[ap1000]

I am continuing to document the day to day happening on my truck with the hope that it is helping someone out there.

Evidently, it was wishful thinking. the CEL popped back on today on the way to work. I am thinking it must be a short. I have no idea how to track it down, but am sure that I can find some info on that on the forum somewhere.

I've read just about every other post I can find on this subject here and keep striking out. If anyone has any other ideas, feel free to chime in.

 

[ap1000]

still have the same code. anyone heard of the wells (brand at autozone) tps having voltage difficulties with oem parts?

 

[ap1000]

a turn for the better...FINALLY.

interesting development. the xplorer starting leaking gasoline today. It had to be the fuel filter the mechanic installed a couple of weeks ago. I got under the truck and discovered that he had cut away the oem fuel clips and installed the new one inline using two 3 in. sections of 3/8 fuel line and a few hose clamps. It really isnt a bad idea b/c now I dont have to have the special tool ford requires to change my fuel filters.... ANYWAY 3/8 line was just two big so it had developed quite a leak. So off I go again to the AUtozone (I'm kinda like Norm entering Cheers now...but anyway) got some 5/16 hose and replaced it on my truck.

Good news is that it seems like my surging/hesitation in the acceleration has gone away

I went ahead and disconnected the negative terminal again to clear the CEL. I'm thinking that maybe I had a vaccuum leak all along at my fuel filter and maybe that caused the sensors to misread. I guess we'll see.

My mechanic keeps telling me to replace my O2 sensors although the codes I keep pulling nor any info I can find here seems to point to that. Should I bite the bullet and replace them? I suppose if they are on the same circuit as the TPS and MAF, then concievably that could be causing my problem, since the computer can't distinguish bad sensors froma bad circuit....

Any Ideas?

 

[Josh]

Well if your having the same problems when your motor is cold then I would say that your O2 sensors are not the problem, not to mention I believe there are 3 or 4 of them and at 60 bucks a pop, that will add up quick. When your truck is cold(Below 170-195 degrees) then the system is in open loop. This means that the computer is not even using inputs from the O2 sensors and is relying on preset values stored in the PCM because they have not had time to heat up. Once the engine warms up to operating temps then the system goes into closed loop and starts accepting inputs from the sensors. Someone correct me if I'm wrong.

 

[ap1000]

interesting. I think you may be leading towards my answer. It seems that my CEL has only really been tripped when the engine was warm, so if the PCM doesn't start accepting input from the sensors until its hot (and trust me it has been hot in alabama for the past several weeks) then I am beginning to believe that it could indeed be my o2 sensors.

Does anyone know if a bad o2 sensor could cause this p1121 code (throttle position sensor inconsistant with Mass Air flow) to be stored?

What does inconsistant mean anyway? inconsistant voltage? inconsistant readings? inconsistant philosophies? I think that would help me out right there.

I've read just about every article on this forum about OBD-II codes, EFI, EEC and the like and can;t seem to find what I'm looking for.

I wish I would have studied this hard while I was in college...

I just love learning. This is a good challenge. Thanks to Brooklyn and Josh for chiming in on this so far... I really appreciate it.

 

[Josh]

There is more than just this forum. Do a search on OBD-II on the internet. You can read more about it there.

 

[BrooklynBay]

Take a look at WWW.FordFuelInjection.Com. They have good information that you should find interesting.

 

[ap1000]

Nice site,Brooklyn.

Another entry in the diary:

Two days ago:

The "acceleration hesitation" has returned as has its comrade in arms: the CEL. Trucks rpms are kinda jumpy on take offs, etc. Hit accelerator and it take engine a second to "catch up" Went to Autozone, cleared the code with the scanner and went to driving. I have noticed that the CEL comes on when the engine is warm. Autozone guy agrees with me that it is probably an air leak. HE suggests I custom fabricate an intake. I say," Yeah, right."

Today:

I have learned that the inconsistancy error is caused by an inconsistancy between the how much the air intake the MAF says there should be and how much air the throttle is actually taking in. PLEASE CORRECT ME IF I'M WRONG. All the info I get is word of mouth or from the internet... so there is room for error here.

SO, I set out to try another cheap fix (I know it has to be something simple), I did the following today:

1. Took the throttle body off today, cleaned it out much better than I did the first time. Last time I didn't take it off. Lazy, I know. Reinstalled.
2. Took off the Air Intake Hose and visually inspected. Looked fine, no cracks, rubber still flexible. It was manufactured in 1999. Is 7 years near the end of its expected useful life? Reinstalled (really tightened the hose clamps) and doubled checked for looseconnecctions. None were apparent.
3. Checked all tubes stemming from air intake. The first is in pretty good shape. The middle tube that runs from the air intake to the IAC. AHA! I think. I check the bolts to the IAC and notice that they could use some tightening. It wasn't loose but defineitey took another 3-4 turns of the bolt. Is it possible to overtighten?? Could this have caused an air leak that would have been the cause of my ills? Only time will tell.
4. Of course I disconnected the negative terminal to reset the PCM.
5. Put her back together and cranked it up. Sounds throatier than it did before. Drove it around and the "acceleration hesitation" seems diminshed. No CEL (for now, at least)

Now, though, when I rev the engine while in park, I hear a strange rattling sound from underneath the truck... (revvvvv...blunh....revvv...blunh) Mark my words, I probably fixed this problem and another challenge has sprung up.

Great.

 

[BrooklynBay]

Check the exhaust underneath the truck for any leaks, or loose hangers. Is your oil level correct? What about your oil pressure?

 

[ap1000]

well, in a fit of desperation I caved in and replaced all 4 o2 sensors because I had to take a long road trip in the truck. Drove home and no CEL. I was thrilled. Woke up the next morning before dawn, cranked her up and in less than 5 minutes, the CEL tripped, no longer thrilled.

Anybody have any good suggestions for how to check for a leak between to MAF and TPS? It visually looks fine, but maybe there is atrick that one of you in cyberspace knows about that I dont. Please let me know.

Think the surging is my tranmission beginning to slip. I am going to change the tranny fluid, and replace the filter and let ya'll know how it turns out.

 

[ap1000]

final post

This will be my final post on this thread.

AFter reading much about tps mods here, I began to think that perhaps my tps was misinstalled from the very beginning.

So, long story short, I end up breaking my TPS I had from autozone. Being honest, I go to buy a replacement, this time from pepboys, and install the sensor.

Been almost two weeks and no CEL. No hard shifting, WOT engages properly.

I got Wells from autozone and b&w from pepboys. I probably never would have caught this.

anyway, I hope this helps someone else out there.

 

[ma96782]

Glad it's working............(BTW, thanks for the up date).......because, I always enjoy hearing, "the solutions" to problems.

Aloha, Mark