P1121 new MAFS and TPS motorcraft

[NicuRN82]

Good Morning. I have a 99 Ford Explorer 4.0 SOHC. We have replaced Mass airflow, cam shaft position sensor, throttle position sensor, and crankshaft position sensor all new motorcraft parts. We are still getting check engine light with code P1121 and when cold it makes this jerking back and forth where it wont accelerate. Any suggestions? Sorry I am not a car person. We want to sell it but I would like to fix the check engine light first.

Thank you for any help.

 

[J_C]

Maybe an intake leak between the MAF and TPS? Did you disconnect the battery to force a relearn and use a scan tool to reset the code?

 

[NicuRN82]

Maybe an intake leak between the MAF and TPS? Did you disconnect the battery to force a relearn and use a scan tool to reset the code?

Yes we did that. The intake is new. Someone mentioned the air intake control valve. That is my next replacememt.

 

[J_C]

Hmm, I'm not sure what an air intake control valve is, unless they meant the IAC, Idle Air Control valve. That is a common recurring thing to need cleaned or replaced every few years, but usually only effects idle, especially when the A/C compressor kicked on was when I first noticed my idle dropping. It had no effect on driving.

Backing up a bit, it was having this problem before you replaced the parts you listed, and the problem is still pretty much the same still? It seems like it's time to hook up a scanner that does real time data, though I'm not sure what to look for if nothing stands out, except looking at LT fuel trims and whether the temp sensors are giving what seems correct values. You might have a little bit low fuel pressure but now I'm just making guesses... at things easier/free to check.

 

[NicuRN82]

Hmm, I'm not sure what an air intake control valve is, unless they meant the IAC, Idle Air Control valve. That is a common recurring thing to need cleaned or replaced every few years, but usually only effects idle, especially when the A/C compressor kicked on was when I first noticed my idle dropping. It had no effect on driving.

Backing up a bit, it was having this problem before you replaced the parts you listed, and the problem is still pretty much the same still? It seems like it's time to hook up a scanner that does real time data, though I'm not sure what to look for if nothing stands out, except looking at LT fuel trims and whether the temp sensors are giving what seems correct values. You might have a little bit low fuel pressure but now I'm just making guesses... at things easier/free to check.

The first time the check engine light came on it was for the camshaft position sensor. We took it to the mechanic they said it was EGR valve and that was replaced. It still threw that code and I dont have 500 dollars a pop to take it to the mechanic so we started throwing parts at it. Replaced MAF, TPS, cam and crank position sensors with advance parts. Also new plugs, wires, and ignition coil. Still had code for camshaft position sensor. Then it was suggested that we needed to replace with motor craft. So we have now replaced all those parts MAF, TPS, cam and crankshaft position sensors with Motorcraft parts. The camshaft position sensor code is gone and now we have the P1121. I do believe they meant the cold air intake valve. It looks like this. I have ordered one.

 

[J_C]

That is also, more commonly known as the IAC, Idle Air Control (valve), with Idle in the name because it primarily, only effects idle. I suppose if it gets stuck it could effect higher RPMs too but I suspect the higher the RPM, the less it's going to matter. I noticed your picture is similar to a listing on ebay. I hope you didn't pay too much.

The Motorcraft branded one is $80 on Rock Auto, but it is made by Hitachi and the same thing under their brand name is $55 +S/H on RA, or even cheaper at $54 on Amazon by getting free shipping. No real reason to pay more for Motorcraft when you can cut out their middleman markup for the same part, just lacking the motorcraft stamped number on the end:

1999 FORD EXPLORER 4.0L V6 SOHC Idle Air Control (IAC) Valve | RockAuto

RockAuto ships auto parts and body parts from over 300 manufacturers to customers' doors worldwide, all at warehouse prices. Easy to use parts catalog.

www.rockauto.com

Amazon product ASIN B00GTHFCGK
Oh wait, Amazon Warehouse happens to have that as a scratch 'n dent box item for a mere $12. I'd buy that in a heartbeat even if you have to pay return shipping on the one from ebay:

https://www.amazon.com/gp/product/B00GTHFCGK/?tag=serious-20

Edit: The forum code may have stripped out the needed URL variables, click on "New & Used (14) from $12.47" on the above linked amazon page to see it. Heh, I'd buy it myself if you don't want it but the IAC changed between '98 and '99 so it doesn't fit mine.

Regardless, I doubt it is the problem, but I suppose it's possible and well worth having a spare for a mere $12. $100, not so much. I have two already but have managed to just clean them out a few times over the years to keep them working so the spare is so I have a clean one to swap on already when I take the dirty one off.

Edit2: For anyone with a '98 4L SOHC (maybe older '97 too?) Amazon also has a Standard Motor Products AC291 for $18 as a warehouse item. It's probably a grade lower in quality than the Motorcraft/Hitachi, but still a deal for someone who needs one.

Amazon product ASIN B000C7Z8M6

 

[NicuRN82]

That is also, more commonly known as the IAC, Idle Air Control (valve), with Idle in the name because it primarily, only effects idle. I suppose if it gets stuck it could effect higher RPMs too but I suspect the higher the RPM, the less it's going to matter. I noticed your picture is similar to a listing on ebay. I hope you didn't pay too much.

The Motorcraft branded one is $80 on Rock Auto, but it is made by Hitachi and the same thing under their brand name is $55 +S/H on RA, or even cheaper at $54 on Amazon by getting free shipping. No real reason to pay more for Motorcraft when you can cut out their middleman markup for the same part, just lacking the motorcraft stamped number on the end:

1999 FORD EXPLORER 4.0L V6 SOHC Idle Air Control (IAC) Valve | RockAuto

RockAuto ships auto parts and body parts from over 300 manufacturers to customers' doors worldwide, all at warehouse prices. Easy to use parts catalog.

www.rockauto.com

Amazon product ASIN B00GTHFCGK
Oh wait, Amazon Warehouse happens to have that as a scratch 'n dent box item for a mere $12. I'd buy that in a heartbeat even if you have to pay return shipping on the one from ebay:

https://www.amazon.com/gp/product/B00GTHFCGK/?tag=serious-20

Edit: The forum code may have stripped out the needed URL variables, click on "New & Used (14) from $12.47" on the above linked amazon page to see it. Heh, I'd buy it myself if you don't want it but the IAC changed between '98 and '99 so it doesn't fit mine.

Regardless, I doubt it is the problem, but I suppose it's possible and well worth having a spare for a mere $12. $100, not so much. I have two already but have managed to just clean them out a few times over the years to keep them working so the spare is so I have a clean one to swap on already when I take the dirty one off.

Edit2: For anyone with a '98 4L SOHC (maybe older '97 too?) Amazon also has a Standard Motor Products AC291 for $18 as a warehouse item. It's probably a grade lower in quality than the Motorcraft/Hitachi, but still a deal for someone who needs one.

Amazon product ASIN B000C7Z8M6

That is great information. I paid 130 dollars and will be returning that for the Amazon one. Thank you so much for the help.If this doesn't fix it should I just sell it with the check engine light on? We have done so much to it. It really will be a great car for someone.

 

[J_C]

In this automobile market, I can't predict what amount of further work is beneficial to offset the reduced value on the market with it having the check engine light on. Some potential buyers wouldn't even touch it with the light, while others might.

On the one hand it seems like value added to have had several parts replaced, but on the other hand, to replace so many and still have a problem... that in itself might make some potential buyers weary. Guess it depends on what's wrong, how costly to fix.

A "good" mechanic should be able to figure it out with an hour of diagnostic time, whatever the rates are in your area so that's what I'd do then with the diagnosis, decide whether to DIY or have it done or leave it as is. This assumes the diagnosis is correct!

 

[1998Exp]

Something is strange here: if the problem is the IAC valve stuck wide open, wouldn't that result in some crazy high idle RPM (which the OP does not seem to be experiencing)?
I have zero experience with the SOHC, but am aware of its failing intake gaskets. Could that be the source of the jerky behavior in cold weather? Does not seem to explain the P1121 code, though, because those gaskets are downstream from the throttle.