Car runs fine under normal load but at highway speed, if you need to accelerate quickly, the car will buck. If you let off on the gas a little, the bucking stops. It seems to be hunting for a gear (automatic transmission). I think it's a vacuum problem but I don't know where to look.
You best bet would be to look for the vacuum diagram and just take a day to make sure all of the lines to the engine and tranny are all correct. If its not it and while bucking the car feels like its going to turn off on you then it maybe a fuel delivery problem.
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Could be a transmission problem or something as simple as bad spark plugs. The engine is under the most load when RPM is low and you are trying to accelerate, such as when it upshifts. You should have the computer checked for trouble codes and hopefully that will point you in the right direction to test. If the spark plugs have more than 50,000 miles of wear you might start with replacing them.
ENGINE HESITATES WHILE ACCELERATION LOSS OF ACCELERATION It can be fuel pressure issue or it's the problem with accelerator pedal or its clogged filters causing there. There are many other possibilities. I suggest you to go through the list of help links mentioned below, these will help you to confirm where the actual fault lies: ------- Jerks and Hesitates During Acceleration? http://technoanswers.blogspot.in/2012/07/2004-dodge-town-country-jerks-and.html ----------- Loss of acceleration? http://technoanswers.blogspot.in/2012/02/loss-of-acceleration.html --------- Headlights flickering and car hesitates to start? http://howtobyme.blogspot.in/2012/02/headlights-flickering-and-car-hesitates.html -------- How exactly the Vehicles Accelerator Cable works? http://repairhelpcenter.blogspot.com/2011/11/how-exactly-vehicles-accelerator-cable.html ------------- How exactly Vehicles Accelerator Pump Diaphragm Works? http://repairhelpcenter.blogspot.com/2011/11/how-exactly-vehicles-accelerator-pump.html -------- 2000 Toyota Avalon: Engine Lean Codes and Knock Sound on Acceleration? http://whatisbyme.blogspot.in/2012/05/2000-toyota-avalon-engine-lean-codes.html --------- 2004 Toyota Avensis: Acceleration And Deceleration makes noise on Front End? http://whatisbyme.blogspot.in/2012/05/2004-toyota-avensis-acceleration-and.html --------- Wheel hop under hard acceleration? http://technoanswers.blogspot.in/2012/04/wheel-hop-under-hard-acceleration.html -------- 2009 Chevy impala accelerator pedal sensor? http://technoanswers.blogspot.in/2012/02/2009-chevy-impala-accelerator-pedal.html --------- Nissan Pathfinder stalls and bucks on Acceleration? http://technoanswers.blogspot.in/2012/02/nissan-pathfinder-stalls-and-bucks-on.html -------- Acceleration lag problem? http://repairhelpcenter.blogspot.com/2012/01/acceleration-lag-problem.html ------------- These details will help. Thanks.
well, there are a few things you can try! a bad tps ( throttle position sensor ) transmission shift issues, bucking, jerking, idle surging,engine cutoff, hesitation on take off, surge while cruising down highway. also be sure your fuel filter is ok! and not plugging up. a maf sensor symtom is surge, slip condition under load, the mass air flow or MAF may be degraded or contaminated. stalling, misfiring, poor acceleration. a light may not come on. you can go to any auto parts store and buy a spray can of maf sensor cleaner. follow directions on can, and this should help alot. good-day!!
sounds like your egr valve is opening too far at part throttle and sticking open. it is actuated by solenoids that open and let engine vacuum in. you were on a good path in checking the vacuum lines. however this may require replacing the egr valve and gasket. the egr valve is circular in shape on top and usually is bolted down with two bolts. its located on the engine side facing the firewall.