LilBit

Hi all. Yes, I said sighing. It's not choking, it's not quitting, it's not stalling, it's not tripping a check engine code or anything. I'll be toodling along, and then all of a sudden, for no reason at all, it's like the engine sighs. It just sighs, for a split second, and then continues running without any loss of momentum. Almost like it quits getting fuel for just a split second. It does it randomly. Sometimes I'll have cruise on, others I won't. It doesn't kick the cruise control off when it does it, either. Sometimes I'll be accelerating, sometimes I won't. It usually happens when I've been driving for more than 45 minutes, and always happens on the interstate. I am not experiencing any loss of power, or loss in fuel mileage.

What could it be?? And should I be worried? I have 267,000 miles on it, and the timing belt and components and head gaskets were replaced about 15,000 miles ago.

cobalt91

Any drop in rpm?

LilBit

Nope. It's literally a split second. Just sort of like a 'thunk' type moment of...well... nothing. I know it sounds weird, but I don't have a clue what's going on, and it's so sporadic. No codes, and I plugged up both the Snap-on MT2500 and the Pegisys and neither are picking up anything weird.

j2b4o

Does it matter how much fuel you have in the tank?? Your sure the rpm's don't drop when this happens?? What does it do if the rpm's don't drop?? Rpms just stay where they were but the car starts to slow??Cars don't really exhale so sighing isnt a great way to describe it, gotta be more specific.

91LS400vgb

That's a tough one. It seems like some sensor is having an intermittent issue - did you have the scan tool connected while the condition was present? I would try to capture the data during the event and look for some evidence in the data streams.

LilBit

It won't do it while the computer is attached. It's like it knows... And I guess if you wouldn't call it a sigh, then a hic, like half a hiccup. It's a very very split second. As for fuel level, doesn't matter. Usually has plenty of fuel as I don't like to go below half a tank, living in rural WV.

mikes7ke

iTrader: (1)

I can't visualize the problem from the description. Though it would be comical if you were driving too fast and the noise was the traction control. By the way, have you ever been low on gas and heard banjos?

LilBit

No. I'm happy to say I haven't.

ArmyofOne

Lilbit, I have a theory...and I think its plausible. Bear with me here.

Power steering pump. How is your fluid level? Sometimes if the fluid level is low enough (or you have a leak somewhere), it can suck air into the system, causing sort of a hiccup. Followed by a whining noise. Then if there is fluid reintroduced to the system (hit a bump for instance), it all goes back to normal.

Just a guess, without actually being there, I cannot TRULY diagnose the car. I will PM cody with this thread and get him in here, as he is better versed in the LS than I am.

mitsuguy

iTrader: (2)

throttle position sensor has a dead spot in it...

chances are if you take your time with a voltmeter or your Snapon/Genisys scanner, you will see a rapid change in voltage at one spot - it may only do it when it is hot or cold as well, so it may be difficult to find...

there are other possibilities, but I've seen this one first hand, and can even duplicate it if I want to when tuning my IS300 - leave a hole in the throttle table and it does exactly as you describe...

PureDrifter

iTrader: (10)

Mitsuguy in the LS forum? AWESOME! lolol

mitsuguy

iTrader: (2)

I saw the bat signal...

timmy0tool

iTrader: (7)

whoa, good answer! never would have considered the TPS.

LilBit

I didn't think about the tps, and actually, I DO have a power steering leak. So I'll fix both of those, and see if that fixes it! I'll let you guys know!