ive changed optispark, coil, ignition control module, plugs/wires, and thermostat... all brand new parts... what could be causing my hesitation? it seems to only be 40-60 mph... when im at a stop or going at a low speed (under 40 mph) there is no hesitation when it give it either a little or a lot of gas... when im going at like 45 mph and i give it 1/2 throttle it hesitates for like 3 seconds and then goes... the rmps dont move for those couple seconds, but the speedometer does go up... at 40-49 50% throttle it hesitates and full throttle its fine... and 50-59 it's kind of the same, just to hesitate instead of 50% throttle it's more like 25% throttle... what u think? please help me

 

I am guessing...Dirty injecters.Try some cleaner,it may help.

 

it's a possibility... but the closed loop/open loop thing doesnt make sense... the car is perfect when i start it up in the morning and it's in closed loop for those couple minutes... ill probably try that... it couldnt hurt... ne1 else

 

Could this be the same problem your having?
I've tried to look at every part in the engine and right now im guessing its the injectors.. It would happen after the car warms up because the amount of fuel the system uses changes from what it has programmed into it (warming up) to what it "judges" to be the right amount of fuel once your car is warm... err at least thats my take on it.

 

yeah it really sounds pretty similiar to whats going on with you... did u try injector cleaner?

 

I used to use injector cleaner every 2nd tank. I don't think it made a difference, but I'm going to try and start using it again maybe with a higher dosage... I believe i had the stumble still when I was using the injector cleaner =/

 

You got it backwards, the ECM is in open loop until the engine gets warmed up and then goes into closed loop. That's so the computer ignores the sensor signals until they settle to correct levels as the engine run's as designed. The only way to really clean the injectors the right way without removing them is to use a cleaner like 3M hooked directly to the fuel rail and pressure regulator defeated and fuel pump disconnected. The vehicle runs off the can of cleaner until it's empty and then shuts off. I have the hoses cost 100.00 for the hook up and 16.00 for cleaner refills. Hooks to the schrader valve. Sounds like to me you may have a bad TPS. Easy to check using an volt/ohm meter. Takes about 5 minutes to check.

 

I forgot to ask, have you confirmed your engine ever goes outof open loop? I've heard of people lowering their operating temperature with thermostats and the computer thinks the engine is still warming up so it keeps enriching the fuel mixture. This would give you the stumble you experience. I refuse to use a lower temp for this reason. If you want cool the engine turn the fans on at a lower temp.

 

O2 sensors. i had a very similar problem when my left O2 sensor failed. that would also explain your closed/open loop problem.

 

ok ill try those things... anyone else think it could be something different?