When I am at a constant highway speed sometimes my car like cuts out and goes lean (doesnt even register on the wideband) Then if i let the rpms drop and go back up its fine for a while...what would cause this??? I thought it might be spark plugs but that didnt change anything....

 

Does it only do this down hill with very light to no throttle input? If so I'd say its normal the car has an injector shut off mode when the car is coasting such as in a downhill moment.

 

No just randomly...almost feels like the ignition is breaking up or something

 

look for a leak after the MAF.

 

Mine does this too, under the same conditions, only it goes full rich. Runs fine otherwise, and doesn't do it all the time.

It's like the airflow is interrupted briefly, only it recovers in just a second or less; I don't think it's something mechanical.

Not to thread hijack, just adding this to see if it helps anyone come up with ideas to the OP's problem.

My car has a Dynoflash off the shelf tune with a K&N and Catback exhaust, otherwise stock.

 

Some things you could check. Vaccum leak (4g63s are plagued with them, boost leak test)Check your EGR. Ever replaced your fuels pumP?

 

well anytime you take your foot of the gas the car will go way lean, or on deacceration. Maybe wanna check the gap on your plugs. Oh, and how long has this been happening for??

 

It sounds to me like it might be the dreaded P0300 code....If you are thowing a check engine light.

Luckly if it is that it is an easy fix. Look in the tuning forum for disable P0300 test.

 

This sounds right... and spark plug gaps and everything are perfect. its been doing it since i can remember its just really annoying

 

Mine happened all the time especially after I would go wot for a second. Mr Fred wrote a write up on how to cure it. If you dont want to disable it. There is another way some are able to tune it out. I simply disabled it and it has not happened since and I am very happy.

 

mine has nothing to do with WOT only during cruising on the highway at the same speed

 

It happened more during cruise after going WOT. It has never happened during WOT. Normally I experienced it btwn 60-75 mph cruise btwn 3000-3500 rpm. It would last until I let my foot of the gas for a moment and then afr, etc. would go back to normal.