I have a 1997, 626 that hesitates and bucks when accelerating. I have replaced the mass air flow sensor and that took care of my idling problem. How do I know if the hesitation problem is the fuel pump, fuel pressure regulator, throttle position sensor or the shaft in the throttle body? Help!!

 

First off, has the maintenance items been done? Items like fuel filter, plugs, cap, rotor, etc... In order to know if it is fuel delivery, you must hook up a fuel pressure gauge and get a reading...like 40psi for example. You will know if the pressure regulator is working by testing fuel pressure while car is running. Monitor your guage and snap the throttle, if it jumps up in pressure about 8psi, it is okay. Also, remove the vacuum line to the regulator and make sure no gas comes out the fitting. To determine things like the throttle position sensor, a scan tool is best. You can see sensor readings on the screen of the tool. The best way to find vacuum leaks is to use basic carb spray or even a mister bottle filled with water. Spray all around the intake, throttle body, and air intake tubes. The engine speed will rise if you find a leak. I would suspect a leak in the rubber intake tube between the MAF sensor and throttle body. Look between the "accordian" parts very carefully for tears or dry rot cracks that let unwanted air in.

 

A hesitation and bucking are two different problems. Hesitation is when you go to accel and does not respond right away. Bucking is generally considered to be a missfire to some degree. As what bkey71 noted, check the basic tune condition more than anything. The spark plug wires in the 97 MY are very prone to failing in both the 4 cyl and V6. Give a check to both the wires and spark plugs paying particular attention to carbon tracking down the side of the white part of the spark plug ceramic insulator. Check I have always used for the wires is to pull the wire lead up out of the well and look/listen down inside the well for spark to be shooting out of the side of the plug wire boot. Have only been zapped a time or two doing this (only hurts for sec ) but is a good and very effective check for ignition spark arcing out of the plug wire boot.

 

Just went through this myself.... I have a 98 2.0L with 118k miles.... tranny was acting real funny ....I couldn't touch the throttle with it downshifting or bucking. My tranny guy said he pulled up the codes and there were two. Missfire #3 cylinder and a cat code (PO421). I did a plug/wire/air filter tune up and the problem went away (piece of cake for a do it yourselfer), but I still get the cat code so I'm in the middle of diagnosing that. The O2 sensors are reading a little high and the rear one took for ever to get a reading.

Good Luck!

 

have you checked your cap rotor and wires?

 

The cap is a high possibility! Ive recently had trouble like this... is there power comeing through all your wires?? this is something you might wantto check... cap is not to costly no worries