roegs

I’m looking for help diagnosing a problem on my 2009 GT manual transmission that I believe is in the accelerator pedal, TPS, or possibly throttle body motor systems. The car has 80k on it. I have the following symptoms:

1. Difficulty starting in first gear. This mostly happens on a warm engine, and while letting out the clutch and giving some gas, the engine suddenly hesitates. I have to push in the clutch and rev it a little higher again to get it going. I’ve driven manuals for many years, so I really don’t attribute it to user experience.

2. When starting out very slow (like pulling into the garage), sometimes when I give it a little gas, it revs up to around 1200 RPM and then slowly comes back down.

3. When cruising on the freeway or in town, the engine suddenly starts slowing down even though I have not changed my position on the accelerator pedal. It’s like I took my foot off the pedal when I really did not. I have to push the pedal a ways to get the engine to accelerate back up again.

4. No error codes.

I’ve cleaned the throttle body several times, and also done the accelerator pedal sequence in the owner’s manual where it instructs to slowly press the pedal down a back up again. Sometimes it seems to help, but only for a while. I've also cleaned the MAP sensor and changed the fuel filter.

I thought that there might be a problem with the accelerator pedal, but opened it up and all the contacts etc look fine. The resistances are in spec. Doing some searches, replacing pedals seems to be a very rare occurrence. I’ve also tested the TPS with an ohmmeter per the shop manual, and it seems to be within specs. Anyone have any ideas?

Nuke

I've yet to experience any of that on either my GT or wife's Pony. Since you said you already cleaned the TB multiple times, I'd give the MAF a few quick shots, then check the TPS. Regardless, run 2 back-to-back tanks with SeaFoam (be sure to run each tank-full down as low as comfortable or at least at or below 1/4 tank. DON'T run it much lower or you'll likely suck tank sediment) and then change the fuel filter (30k-40k on a filter is often typical if you tend to pull gas from the bottom of your tank often).

Are you running any mods?

roegs

Nuke...thanks for the note. I'll check the MAF again. I did try disconnecting the battery for an hour this evening. Doing so did help the hesitation when starting out in first gear, but the other flat spot problem was still there. While driving at a steady speed on the highway this evening the car would suddenly feel as though I had let off on the gas pedal. I'd then have to push down on the pedal a ways before I could feel it accelerate again. I keep thinking that it feels like the control module loses its signal from the gas pedal, but if that were the case, it should log an error code with the accelerator pedal circuitry. I'll also give the Sea Foam a try. Car is completely stock...no mods.

roegs

The good news is that my car is now running better than it ever has since I owned it (bought it a year ago with 78k on it). The bad news is that I violated my own troubleshooting policy by doing two things and now I'm not positive as to which fixed it. First thing I did was remove the TPS and connect it to an analog ohm meter. As I moved the TPS, I could see that it was a little notchy at the beginning of its travel (low speed where the throttle plates are mostly closed). I was able to get it smoother with compressed air while working the TPS back and forth. Second thing I did was remove the accelerator pedal and clean the contacts. My best guess is that the TPS was the source of my problems and I'll probably order a new one. I only have a few miles on it so far, so I'll keep driving for a few days and make sure the problem is really gone...

Nuke

Thanks for the update and good going on the fix(es).