Throttle drops off quickly - Normal? ECU issue?

[Hirudin]

By the way, I tried searching but couldn't find any posts relating to my prob...

Howdy everyone! I finally bought a Speed3! ('07 GT, 15,000 miles, $19,600, Silver)

I bought the car in Texas and drove it home to Albuquerque, NM (~1000 miles). Just got back last night, god was that a long ass drive!

When I got to Albuquerque there was a small stretch of stop and go traffic which is where I noticed this problem... At low speed when I release the gas pedal the RPMs slow suddenly which causes the front of the car to dip down and the car slows. I didn't notice it until Albuquerque, but before then I wasn't ever in stop and go traffic.

This morning I reset the ECU (removed negative cable from the battery and pressed the brake a few times). I'm pretty sure the reset was successful because the trip odometer was cleared. I drove around my neighborhood: (I left when the temperature was a little above "C") when I left my driveway it was fine, but when I got back the problem had returned.

I have a couple hunches as to what the problem could be...
- Maybe something to do with the octane rating of the gas? While it was in Texas it got noting but 93, here in New Mexico the highest available is 91.
- Could there be something wrong with the clutch? I'm not too good with the clutch yet. I don't think I'm horrible, but take-offs aren't perfectly smooth.

The slowing feeling is similar to when you start moving from a stop and you've released the clutch improperly and the car sorta jerks forward, then slows, then jerks forward, then slows, etc. But it doesn't jerk forward and only slows down once.

 

[Kosh]

Is your AC on? Since the compressor is run off a belt from the engine that could slow the car when you get off the gas.

When you take your foot off the gas while still in gear the wheels turn the drivetrain which turns the engine. That power from the wheels is getting lost turning the compressor as well as the engine.

 

[Hirudin]

Is your AC on?
...

Thanks for the reply! It was indeed on, but it was also on for the rest of the trip. It's possible I turned the A/C up though.

I'll drive it around some without the A/C to see if it goes away.

My buddy said it might be a vacuum leak causing it to run too lean. Maybe the elevation change (from ~0ft to >5000ft) is playing some part as well?

 

[fourthmeal]

Nah...you'd get some nasty CEL's from this car if you're running lean, I imagine.

Chances are its the fact that you're running a manual transmission car and you're not used to it yet. Engine braking is pretty strong on this car, especially at the lower 3 gears.

Oh yeah at 15K miles, go check your air filter, because in the south the dirty air might be choking the filter.

Also, double check that you didn't have the emergency brake partially pulled up, because that would cause massive slowing when off throttle.

You can verify everything is ok by kicking up to about 45, go to 5th, let off the gas, and coast. You should make it pretty far.

 

[fourthmeal]

how did this turn out so far?

 

[khaydin]

When I got to Albuquerque there was a small stretch of stop and go traffic which is where I noticed this problem... At low speed when I release the gas pedal the RPMs slow suddenly which causes the front of the car to dip down and the car slows. I didn't notice it until Albuquerque, but before then I wasn't ever in stop and go traffic.

I think that's normal, it is for me atleast. When you're in first and second gear in stop and go traffic don't just suddenly take your foot off the throttle otherwise the car will start slowing very rapidly causing that rocking back and forth feeling. Just slowly ease off the throttle and it should slow much smoother.

I think what causes it is our rear motor mount, it gives way too much. When you take your foot off the throttle or push the clutch in it causes the engine to move about a bit. The engine moving around a lot messes with your shifts and makes sudden engine braking seem a little harsh.

 

[chacon101]

I don't think anything is wrong with your car at all. All of my manual transmission cars have done this and because of the power in this car, it's just more obvious. Don't worry about it and learn how to drive smoother (drive2)

 

[BlackCherry06]

I've learned that this car, more than any other of my M/T cars needs to have feathered throttle if you're going to slow down without depressing the clutch. An abrupt throttle lift at low speed causes heavy engine braking that feels as if you've slammed on the brakes. But believe me...you rather have this than the opposite. For emissions reasons, some cars are programmed to hold RPMs after throttle lift, and that's more of a pain IMO.

 

[Hirudin]

Oops... didn't realize this thread had so many more posts...

I think I may have gotten use-to the problem or trained myself to avoid it or something. Every now and then I'll feel it, but now the slowing seems less abrupt or something.

Oh, I've also been driving around with the 'Auto' A/C turned off. The A/C is still on, but on low.