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Old 12-12-2006
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Join Date: Nov 2006
Location: california
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CEL & P1121 Code...after new TPS

I recently had a thread about a, well, as it was rightful tagged, a "self induced" CEL...but hey how else can I understand how this stuff works. :)

Anyway I had to replace the TPS because I croaked it when I looked at it...oh, well. That has let me add a bunch of new tools and toys to help with the upkeep of my new to me truck. It's a '97 Supercab w/4.0l, 3.55 and 2wd.

I was happy that everything was running smoothly until the other day. The CEL came back on...crap. First thing I read the codes and this time it was a different code. It was P1121. The code xlates as "Throttle Position Sensor Inconsistent with Mass Air Flow Sensor" whatever that means.

I thought maybe the MAF might need cleaning so I cleaned it using MAF cleaner. Until coming here I never even knew there was a MAF let alone what it did and how to maintain it...but cleaning it still returned the code and eventually the CEL after I drove the truck. My assumption is the PCM wants to have the device fail a couple times before it flags the error.

I discovered that I could exactly reproduce the error. It would only start happening during highway acceleration. In town I never needed to use enough throttle to trigger the code.

I did reading online and honestly found little to nothing about this error code. Well, I used to write software for a living and one of the things we knew as true was you can never completely trust an error code. So, I assumed there was nothing wrong with the MAF and focused on the TPS.

I am ashamed to admit I bought the part at, gulp, Kragen. I only did so because that was the only place in town that carried the shop manual. Anyway, I thought I would look-up the part on their site just to make sure of the warranty/return policy. Darned if the site showed two different Motorcraft part numbers for the TPS. The first TPS they gave me begins with F4sf-Aa and the old TPS was F57Z. They also show the F57Z part for the engine.

Short story long, new and correct sensor stopped the CEL & error codes. Took it on a short 20mi drive just to be sure and hit it hard a few times...no codes...viola she is a-fixed.

Why write this...I learned another thing about car repair...never trust the parts store to give me the right part. From now on, I will make sure I know the Motorcraft part number before I go get the part. Plus I never go to Kragen in town have always dealt with NAPA over the years and they have a good rep here for knowing what they are doing. Costs more but it's worth the extra most of the time since I can ask a question and well, the lights are on and there IS somebody home. Not like Kragen where they only know what is on the screen.

Just wanted to pass on what I learned for the others like myself on the short-bus end of the learning curve...

Tomorrow I Seafoam...that I have done before though...
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Old 12-12-2006
n3elz's Avatar
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Join Date: Jun 2004
Location: Kennett Square, PA
Posts: 10,620
Hey, good job. I was going to tell you to pull the battery and reset the PCM and try it, lol.
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