Off throttle hiccups

[Kooldino]

About a year ago, I started experiencing a minor (but annoying) issue with my car. At times, when I would be in a gear at say, 4000rpm and let of the throttle, the car would continue to get gas.

Normally, if you were in 3rd gear at 4K rpm and let off the throttle, your wideband would show that you were full lean (since the injectors weren't firing any fuel) and the car would decelerate normally.

However, with the issue I was having, I would still maintain a 14.7:1 AFR, and the car would decelerate more slowly. Other times, it would go full lean as it should, however it would hiccup a few times on the way down from 4K rpm to 2K rpm, due to a few small squirts of fuel going into the motor.

Using my Auterra PDA Scan tool, I discovered that the TPS (or Throttle Position Sensor) voltage would spike during the "hiccups". It would go from 0 (when I was off the throttle) to fractions of a volt - just enough for a quick squirt of fuel.

I figured my TPS was going bad, so I replaced it. No help. I tweaked the angle of the slotted holes that the TPS sensor sat in. I tried adjusting the "closed" position of my throttle body, and I vaguely recall playing with the throttle cable. The only result of my tinkering was an erratic idle (lesson - don't mess with the position of the throttle plate!).

I went ahead and replaced the entire throttle body with sensors that were properly calibrated and set. My idle returned to normal, etc. However, I still have the issue where I get the quick spikes from my TPS which result in the hiccup. The only think I could figure to do at this point is to try messing around with the throttle cable again...perhaps it's too tight.

(dunno)

Any ideas?

[Kooldino]

I loosened up the throttle cable a bit, got rid of 80% of the problem.

[Fudgie]

Have you determined whether its the MPI adding the fuel or the stock injectors? Maybe try unplugging your extra injector (obviously staying out of boost!!) and take it out for a rip and see if your problem persists. Any chance the injector might be a lttle shitted up and not closing quickly enough when you take your foot out of it?

[Kooldino]

Have you determined whether its the MPI adding the fuel or the stock injectors?

Being as the TPS spikes would coincide with the extra fuel thrown, it would definitely be the stock injectors.

My MPI isn't even set up to add fuel until....

1-I hit boost
2-at 30% throttle or greater
3-at 2500rpm or better

I could make this issue appear and not satisfy any of those 3 conditions.


Maybe try unplugging your extra injector (obviously staying out of boost!!) and take it out for a rip and see if your problem persists.

I'm pretty sure I tried this last year, and it wasn't the mpi.


Any chance the injector might be a lttle shitted up and not closing quickly enough when you take your foot out of it?

Yes, but it's not likely. The clear culprit here was the fact that I'd get TPS voltage spikes at the same time as the fuel.

[Fudgie]

Just so I understand- 80% of the problem was fixed by loosening the cable? Are you still getting some tps spikes when you let off the gas? I never really looked- but is there a throttle stop screw that might be out a little too far leaving your tps on the hairy (yes, I said hairy) edge?

[Kooldino]

Just so I understand- 80% of the problem was fixed by loosening the cable?

Yessir


Are you still getting some tps spikes when you let off the gas?

I'll check today. I haven't been nearly as annoyed by it, so I didn't hook up my tool to it lately.


I never really looked- but is there a throttle stop screw that might be out a little too far leaving your tps on the hairy (yes, I said hairy) edge?

That could be, but I've adjusted that screw in the past on my last TB and had bad results. :/

[Maxx Mazda]

That's a wierd problem... My car did that after the Haltech install, so what I did was hold the gas down so the TPS would say like 2%. Then zero it out. Go to ful lthrottel, and hit set and that would be 100%. So now it shows 0% throttle like a HAIR before i actually take my foot completely off the pedal.

That was for the Haltech, but I'm wondering if there's a way to calibrate the factory ECU in the same manner... There must be.

[Maxx Mazda]

Failing that, I'd suspect noise in the TPS signal wire... Maybe check it back to the ECU for a fray?

[jamesk]

this kinda happened to me, but the problem went away since i reinstalled my intake manifold.

i would rev my car from the engine playing with the throttle body, but then i realized that when i closed the throttle body, it was not 100 percent closed, but the gas pedel was not being touched, so that threw off my tps sensor a little bit.

so everytime i play with the throttle body, i have to make sure it is fully closed so it is the same with my gas pedal.

do cables go bad or strech out over time?

[Kooldino]

That's a wierd problem... My car did that after the Haltech install, so what I did was hold the gas down so the TPS would say like 2%. Then zero it out. Go to ful lthrottel, and hit set and that would be 100%. So now it shows 0% throttle like a HAIR before i actually take my foot completely off the pedal.

That was for the Haltech, but I'm wondering if there's a way to calibrate the factory ECU in the same manner... There must be.

There isn't. :/

[Kooldino]

this kinda happened to me, but the problem went away since i reinstalled my intake manifold.

i would rev my car from the engine playing with the throttle body, but then i realized that when i closed the throttle body, it was not 100 percent closed, but the gas pedel was not being touched, so that threw off my tps sensor a little bit.

so everytime i play with the throttle body, i have to make sure it is fully closed so it is the same with my gas pedal.

do cables go bad or strech out over time?

If it stretched it wouldn't cause the issue. That would only occur if it shrunk.

[Kooldino]

Failing that, I'd suspect noise in the TPS signal wire... Maybe check it back to the ECU for a fray?

It's a possibility, being as it's fractions of a volt.