Help diagnosingfuel system issue (OBDII code 0121)
 

Hey all,

I'm having some uncertainty in diagnosing a fuel system issue, and I want to
make sure I'm on the right track before I start spending actual money on
parts that may or may not fix my problem.

My '98 TJ has an erratic idle, and stalls when cold (first half minute or
so). Occasionally, at speed, it bucks (only once each time); otherwise, it
runs great. The MIL is lit. I borrowed a friend's OBDII scanner and it
reported code 0121. According to what I can find, this means that the TPS
doesn't agree with the MAP sensor. If I disconnect the TPS, it behaves
identically. If I disconnect the MAP sensor, I can't keep it running at
all.

So I'm thinking that I need a TPS. However, since it doesn't say that the
TPS has failed, only that it disagrees with the MAP sensor, I'm hesitating.
It's a $50 part, and I want to be sure it's the right one to replace.

Are there any other tests I can do to nail it down? Has anyone else had
this code, and what ended up being the root cause?

Thanks so much!

Hal

Re: Help diagnosingfuel system issue (OBDII code 0121)
 

replace the tps disconnecting the map and it stalling means the map is ok

Hal Haygood wrote:

> Hey all,
>
> I'm having some uncertainty in diagnosing a fuel system issue, and I want to
> make sure I'm on the right track before I start spending actual money on
> parts that may or may not fix my problem.
>
> My '98 TJ has an erratic idle, and stalls when cold (first half minute or
> so). Occasionally, at speed, it bucks (only once each time); otherwise, it
> runs great. The MIL is lit. I borrowed a friend's OBDII scanner and it
> reported code 0121. According to what I can find, this means that the TPS
> doesn't agree with the MAP sensor. If I disconnect the TPS, it behaves
> identically. If I disconnect the MAP sensor, I can't keep it running at
> all.
>
> So I'm thinking that I need a TPS. However, since it doesn't say that the
> TPS has failed, only that it disagrees with the MAP sensor, I'm hesitating.
> It's a $50 part, and I want to be sure it's the right one to replace.
>
> Are there any other tests I can do to nail it down? Has anyone else had
> this code, and what ended up being the root cause?
>
> Thanks so much!
>
> Hal

Re: Help diagnosingfuel system issue (OBDII code 0121)
 

replace the tps disconnecting the map and it stalling means the map is ok

Hal Haygood wrote:

> Hey all,
>
> I'm having some uncertainty in diagnosing a fuel system issue, and I want to
> make sure I'm on the right track before I start spending actual money on
> parts that may or may not fix my problem.
>
> My '98 TJ has an erratic idle, and stalls when cold (first half minute or
> so). Occasionally, at speed, it bucks (only once each time); otherwise, it
> runs great. The MIL is lit. I borrowed a friend's OBDII scanner and it
> reported code 0121. According to what I can find, this means that the TPS
> doesn't agree with the MAP sensor. If I disconnect the TPS, it behaves
> identically. If I disconnect the MAP sensor, I can't keep it running at
> all.
>
> So I'm thinking that I need a TPS. However, since it doesn't say that the
> TPS has failed, only that it disagrees with the MAP sensor, I'm hesitating.
> It's a $50 part, and I want to be sure it's the right one to replace.
>
> Are there any other tests I can do to nail it down? Has anyone else had
> this code, and what ended up being the root cause?
>
> Thanks so much!
>
> Hal

Re: Help diagnosingfuel system issue (OBDII code 0121)
 

replace the tps disconnecting the map and it stalling means the map is ok

Hal Haygood wrote:

> Hey all,
>
> I'm having some uncertainty in diagnosing a fuel system issue, and I want to
> make sure I'm on the right track before I start spending actual money on
> parts that may or may not fix my problem.
>
> My '98 TJ has an erratic idle, and stalls when cold (first half minute or
> so). Occasionally, at speed, it bucks (only once each time); otherwise, it
> runs great. The MIL is lit. I borrowed a friend's OBDII scanner and it
> reported code 0121. According to what I can find, this means that the TPS
> doesn't agree with the MAP sensor. If I disconnect the TPS, it behaves
> identically. If I disconnect the MAP sensor, I can't keep it running at
> all.
>
> So I'm thinking that I need a TPS. However, since it doesn't say that the
> TPS has failed, only that it disagrees with the MAP sensor, I'm hesitating.
> It's a $50 part, and I want to be sure it's the right one to replace.
>
> Are there any other tests I can do to nail it down? Has anyone else had
> this code, and what ended up being the root cause?
>
> Thanks so much!
>
> Hal

Re: Help diagnosingfuel system issue (OBDII code 0121)
 

Okay, that makes sense. Thanks! I'll let y'all know how it turns out.

Hal

"mic canic" <dbrider@cac.net> wrote in message
news:400AF5D5.5D39ED88@cac.net...
> replace the tps disconnecting the map and it stalling means the map is ok

Re: Help diagnosingfuel system issue (OBDII code 0121)
 

Okay, that makes sense. Thanks! I'll let y'all know how it turns out.

Hal

"mic canic" <dbrider@cac.net> wrote in message
news:400AF5D5.5D39ED88@cac.net...
> replace the tps disconnecting the map and it stalling means the map is ok

Re: Help diagnosingfuel system issue (OBDII code 0121)
 

Okay, that makes sense. Thanks! I'll let y'all know how it turns out.

Hal

"mic canic" <dbrider@cac.net> wrote in message
news:400AF5D5.5D39ED88@cac.net...
> replace the tps disconnecting the map and it stalling means the map is ok