Dtc P1120

[Jimmy]

So I've been having a crazy high idle lately, and the CEL came on the other day. By crazy high, I'm talking 1700-2200 rpm...the normal is 700-900. Anyway, I got 2 DTCs back. One was a bad TPS (Low input or something), TPS replaced and the code hasnt come back since I cleared it.

But this other one I cant narrow down. P1120, Manufacturer Contl Fuel Air Metering. What exactly is this related to? My first guess is a bad/dirty MAF, or the MAF is reading a different amount of air than what's actually getting into the system (like there's a leak).
I recently installed an intake, but I'm pretty confident I've got good seals all around, and there was about a week in between the installation and the problems.

What else should I be looking at?

[TXFO]

P1120 is TPS out of range.

[Jimmy]

Interesting. Well, I've got 2 more TPS codes to go along with that one now:

P0122 TPS/Pedal Position Sensor A Circuit Low Input
P0123 TPS/Pedal Position Sensor A Circuit High Input

Ok, so obviously there's a problem with the TPS. And yet, its brand new. What now?

Hmm...could this be related to an aftermarket throttle body? After reading the description it sounds like 1120 is related to the butterfly's position...adjust the idle maybe?

[TXFO]

its probablly a wiring problem.

[TXFO]

have you been using a larger TB? did the codes start after the installation of one?

[Jimmy]

have you been using a larger TB? did the codes start after the installation of one?

Yeah, about 3 or 4 years after installing it. I'm running one of those Mustang GT TB setups that Gigahertz sold years ago. But the CEL is new.

[TXFO]

wiring problem then.

[Jimmy]

So what kind of a wiring problem am I looking for? A bad ground would be a good place to start, but aside from that, what else is there? I guess checking the PCM connections, but that's not likely to be the issue.

My aftermarket tach has been acting up lately (sometimes it goes blank, sometimes it just reads zeros)...could that be related? Does the TPS share anything in common with whatever the PCM uses for tach output?

[TXFO]

your tach gets its signal from the wire going PCM to cluster?

Id expect to find a break in one of the 3 wires. best bet is point to point resistance test.

[Jimmy]

your tach gets its signal from the wire going PCM to cluster?

I believe so. I remember running a wire to the PCM when I installed it. I want to say Pin 42 or 48 or something like that...its been a couple of years.

[nate]

I seem to remember having an issue something like this and ended up going to the local auto shop. He sparayed some carb cleaner around the back of the engine looking for vacuum leaks. Turned out there was a split in the hose at the bottom of the intake manifold which comes out the side of the motor under the distributor. The other thing is the voltage of the TPS being set right due to the position of the slot related to the butterfly position if you have an aftermarket TB. One more thing is the IAC aka idle air control which I have taken out and cleaned with PB blaster then a little brake cleaner and put back in. Just some ideas to work with.

[Machine0316]

id look for leaks first (loose clamp or hose), iac, and even the dpfe.

[Jimmy]

Does anyone know what the TPS signal voltage is supposed to be at idle?

[Jimmy]

Well, after dorking around with it, I compared the old TPS to the new one...they are not the same. The replacement SPI TPS turns one way, the one I pulled off my car turns the other way (the correct way for this throttle body). So the CEL came on because the TPS wasnt doing a damn thing, because its the wrong one. So I put the old one back on, and have rechecked the codes several times (swapped them on Saturday). No codes yet.

I'm baffled, but the problem is (at least temporarily) resolved. Idle is normal, no CEL or DTCs, and I have a spare SPI TPS.

Edit: Checking the voltage was what tipped me off to compare the 2 sensors in the first place...good call.