[Uberriser]

Issue: Random hesitation

Conditions:
1. Occurs/Noticeable when engine is cold (sat overnight for example)
2. Light to part throttle
3. Most noticeable between 2100-3000 RPM
4. Goes away or can't detect it when engine is hot
5. No engine codes

It seems to be a sensor that is delivering data that is in spec (but wrong for conditions) to the ECM. Perhaps temp related. Swapped out the MAF with a known good unit. No change. Swapped out 02 sensors with known good units, again no change. Swapped out PCV - no change.

I have monitored air inlet temp and it make sense...the coolant temp makes sense.

I do wonder if it isn't the engine but something else like the rear diff or the braking system.

This is more annoying than anything...any ideas? Because the dealer doesn't have any.

Sam

 

[JimT]

Our cars (as do all current vehicles) have to meet a very strict emission hurdle in the first 90 seconds of operation. The objective is to have the vehicle in what’s known as “closed-loop” early so exhaust control can do its job. This at times find the engine running a little lean cold due to this process. A little like you pushed the choke in too early... you’re right, in-specs, computer control, probably normal.

 

[Uberriser]

Our cars (as do all current vehicles) have to meet a very strict emission hurdle in the first 90 seconds of operation. The objective is to have the vehicle in what’s known as “closed-loop” early so exhaust control can do its job. This at times find the engine running a little lean cold due to this process. A little like you pushed the choke in too early... you’re right, in-specs, computer control, probably normal.

Thanks Jim...this does happen well into the first 5-10 minutes of operation...until the oil basically comes up to about 150 degrees or so. I suppose I would feel better if everybody was experiencing the same issue. My neighbor who has the same car doesn't.

Speaking of which, you and I have nearly the same car if not the same. Great color combo. Older pic of mine...now has GT350R brake calipers.

 

[JimT]

Yeah, my dream color/ car... matches the pavement. Lol.

Well it sounds like you have pinpointed your abnormality pretty well. All you need is a friend with an OBD II scan tool with data record to take a snap shot of the concern during the event. It can be diagnosed if someone gave it the time. It being intermittent also puts an additional wrench into any diagnosis.

 

[SilverSerpent]

Thread necro but I am having this issue as well. This thread here also came up during Googling, and I think people are way off thinking it's just some lack of torque nonsense.

Happens between 2000-3500 RPM. Under light - medium throttle during acceleration. The car gets a bit of a hesitation and it feels like the power is cutting in and out. My initial thoughts were something like detonation or other combustion issue (as I had a Subaru that exhibited the same behavior prior to breaking ring lands), traction control kicking in (since I first noticed it in wet conditions) but never saw a light, the A/C compressor suddenly cycling on/off/on or ignition timing related. Someone in that thread mentions a cam profile switch over which I could potentially see causing it? It's more noticeable when engine is cold-ish but still does it at operating temp.

It feels like there is something wrong. Like a subtle bucking. You'll be accelerating from a stop, smooth throttle operation, then in 2nd & 3rd around 3k RPM you'll feel the power fall off and then come back on once or twice like a switch. Like some kinda weird electronic throttle/engine control bs is acting up.

2,800 miles on the car and I bought it a couple months ago with 1,500. Took it to local dealer for post-purchase inspection (I bought it out of state) and I, like an idiot, didn't even think to mention it as I had just got the car and thought it was the A/C or something weird. They didn't find any issues with the car.

 

[RJY]

Sam and SilverSerpent, have you guys identified a resolution to the "hesitation" question? I thought I was imagining this, but my car does/has this condition too. I haven't taken it in to the dealer yet, so wondering if you guys have found out anything.

Also, anybody on the forum experience a engine rattling sound between 2000-2900 rpm under slight load? Lessens has car is up to operating temperatures, but still there under light load or you can sit idling, lightly rev the engine to 2000 and hear it. Thanks guys.

 

[DE350]

Silver Serpent,
There is a technical service bulletin regarding this problem. Look up TSB 19-2135. This is caused by transmission output flange nut that has come loose and this gives an erroneous signal to the computer. I just had the transmission nut replaced under warranty and that fixed the problem. I love my car again.