Engine Shuddering at Hard Braking?

[niteflite]

During my stop and go drive into work this morning, i felt a shuddering of the engine when i broke harder than usual to come to a red light. The car had been adequately warmed up (this was after at least 5 miles into the drive), the ac was on a low setting. Lights weren't on, etc. A very routine drive.

Does anyone know what could cause this? I had this happen to me a couple of times on one of my previous cars. I think it was a problematic fuel line that had been in the shop for repairs post-accident and for a recall that might have done it.

 

[Ron5.0]

Could be a lot of different things going on, could be related to fuel.

But first of all if your still under warranty just take it in

 

[NSXNEXT]

Shuddering as in it felt like it was stalling?
Do rpms drop suddenly?

 

[niteflite]

Shuddering as in it felt like it was stalling?
Do roms drop suddenly?

Yes, as if it was about to stall. I don't remember rpm dropping or not since it happened so fast. I did put in some chevron pro guard before filling up my current tank of gas. this was before the oil change i got done 6 days ago.

 

[NSXNEXT]

I'm going with an issue with the brake vacuum booster BUT you need to have the dealer look at it.

 

[mikec]

With the engine warmed up and idling, mash the brake pedal firmly several times, fairly quickly. If the RPMs wander, then power brake vacuum assist is likely the issue. No engine change? Probably something that is responding to the "g" forces from rapid deceleration. Off hand, nothing definite jumps to mind.

Most cars have some sort of roll-over sensor to kill power to the fuel pump or block fuel flow (don't want to be spewing gas through busted fuel lines in an accident); maybe that's too sensitive? Especially if you stand on the brakes while going downhill; the apparent "g" forces sum together. Cutting off the fuel flow for a moment will make the engine stumble a bit. Crud in the fuel tank may slosh around and block the pick-up though that is rare: the screen filter on the fuel pickup is usually pretty large so it's hard to block the whole thing at once.

Mashing the brakes when the gas tank is almost empty could slosh the fuel away from the pick-up, again magnified if the vehicle is going downhill.

mike c.