Our IS has had a consistent problem with stalling while at speed, and sometimes on acceleration. Took to the shop it got so bad, they cleaned injectors, plugs etc and low and behold, it now runs like a bat out of hell but the stalling problem still exist, just not as bad. The car is still drivable, but the slight pausing is annoying. Its now has a warranty, but when I called the shop they said it has to be in the computer, and only the dealer can fix it. It seems when the engine is cold it doesn't occur, just when it warms up. Suggestions to fix is appreciated. .

 

Bad cam or crank sensor. Could even be a crack in the contact board on the APP or TPS sensor. Have seen this a few times over the years.

 

I would assume that you're well over the 150,000 mi. mark, and you stated that you had the spark plugs replaced; one thing that can happen when removing one of the 3 ignition coil(s) (on-plugs)... is that the ignition coil (on-plug) BOOT(S) CAN CRACK, at which point when the engine reaches N.O.T. (Normal Operating Temperature), mid ranged N.O.T. or just even a warm, humid atmosphere, or whatever these days... and that cylinder is on its ignition stroke, the electrical current that was once supposed to go to the spark plug and burn the air fuel mixture now y's off (taking the least path of resistance (where resistance increases as heat increases) and will ark off of the exhaust or intake cam cover, or the cylinder head, throwing a check engine code for a misfire and a bunch of other problems.

START OFF BY BEING IN A NOT SO BRIGHT ATMOSPHERE E.G. A GARAGE OR UNDER THE SHADE OF A TREE (FOR BETTER VISUAL IDENTIFICATION!!!)

if you have access to an Allen or Torx bit set then,

1‐ Remove the 4 Allen bolts that hold on the timing belt cover... (under the oil filler cap), as well as remove the oil filler cap.
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2- Re-install the oil filler cap.

3- Start the engine, then observe for the ARK (misfire.. whatever), it might help to REV the engine from the throttle body.

You should be able to see which of the 3 coil over plug packs it is, every time that it occurs and if so... go to the dealership or go to Rockauto.com and put in the Make, Year, then Model, click on Ignition, click on Spark Plug/ Coil-on-Plug Boot and either buy 1-3 of the NGK Brand or buy all 3 of DENSO, !AND WHATEVER YOU DO, DONT USE ANYTHING TO CLEAN THE NEW BOOT!!! GOOD LUCK, let us know if it worked.

4 bolts.

Oil filler cap.

Under hood throttle components.

Rockauto.com

 

Wow..Ill certainly give it a shot. And yes, the mileage is close to 250K. Thanks for all the help! Rick