has a tendency to stall when at a stop. allways restarts with no problem. sometimes car acts up really bad where it seems like the mixture is to rich/lean or maybe engine isnt recieving enough fuel? push accel to floor and car will act like a 4 cyclinder, no power at all. problem is interment doesnt always run like this sometimes its real bad and sometime it runs good. IAC? TPS? fuel filter? EGR? recent tune up was done. plugs wires cap rotor were all replaced 2 weeks ago. why is this car doing this? had problem last week, MAP sensor failed. replaced part car ran great for 1 week then started acting up again MAP sensor was out of my s10 blazer, used but a matching known working part. NO CODES STORED which doesnt help me any. when i picked my wife up i let the car idle the idle was up down not steady. car has a slight "tach twich" when at idle, wont maintain constant engine speed, its close but you can see the needle movement a little. any help or advice on what i should replace/check next would be great thanks

 

check for a vacuum leak

 

I had a Fiero GT with a V-6 automatic and it did this two times. The first time my catalytic conv. was completely stopped up. It got red hot under the car after 30 minutes of driving and would stall at idle. It also at times had no power and would barely mantain the speed limit. The second time my computer was stuck in some loop mode and I replaced it with a used computer. It had all the same symptoms.

 

I would say a vacuum leak, plug wires crossed, or a bad injector.

 

it could also be the stator in the torqueconverter if its an auto they tend to cause the car to sputter as you come to a complet stop and than finally stall. the stator is repsonsible for channeling the fluid through teh converter sand if its really bad could cause quite a bit of performance loss.