ok, starting from the begining, iv replaced the thermostat, water pump, plugs, wires, O2 censor, and the throttle position censor. when i start the car up, cold or hot, when im in park or nuetral it runs really rough, like hesitates.. it still does it when im at a dead stop, but when im the throttle it runs great... the only thing i can think of that i havent replaced is the fuel filter... any idea's - tips..?
thanx much..
-Joe

Why did you replace the parts? When did the problem start?

Does it run rough or hesitate? Two different problems?

Norm

When the TPS was replaced, was it calibrated? Idle voltage needs some fine tuning when replacing the TPS sensor. If its not calibrated properly, it can trip the computer into error mode at idle.

(BTW, are you getting any error codes from your ECM?)

The 3.1's are also notorious for vac. leaks in the upper intake plenum area. There are 3 plastic hoses that go into the throttle body, and these make a 90 degree bend to go under the plenum, and those little lines will crack too. Best check is to get a can of carb cleaner and spray the area between the plenum and the lower intake. If it revs up, you have a leak. Other common symptoms of this condition are increased fuel consumption and poor accelleration. The car is slow to begin with, so you may not notice it as much, that is, until its fixed. One thing to watch for though, if that is the problem... the plenum bolts are also notorious for breaking off. Be sure to douse them all in penatrating oil before taking them off. You will need a torque wrench for reinstallation. One more note about this... The plenum will likely be all carboned up, as well as the EGR valve. If you do decide to go down this road, take the time to clean all this out. Oven cleaner is your friend, and let it sit for a while before scrubbing it all off. Carb cleaner is also a good rinse for this, and wont hurt the EGR valve.

A fuel filter problem would cause the oppisite symptom. The car would possibly idle ok, but when you get on it it would run like crap. Replacing it is still a good idea, as that is regular maintence.

88delta88's idea is also very good, and should probably be the 1st thing you look at seeing as you have already replaced it.

If you have replaced all these parts to try to cure the idle problem, this should be a good, albiet expensive lesson to diagnose and find the real problem before "shotgun diagnosing" or chucking parts at it.

Also, as Norm asked, can you give us more background?

Regards,

Andrew

Don't know if this would apply, but do you have a crank sensor? Is that the same thing as the throttle sensor?
My 99 Olds Intrigue had the crank sensor replaced a few times.
Actually, it's starting rough again, but same thing...once it's running, not a problem.
If you have it figured out by now, please post the solution...maybe it is the same thing I need to do.
Di

Hi Di, all,

Welcome to TOC.


We don't know if it would apply either, we don't have enough information yet. Yours or his.


Crank sensor is for ignition, throttle position sensor is for fuel mixture.


Didn't you test the first one, before you replaced it? Simple test with a VOM. Didn't the third changeout tell you anything? I suggest you take it elsewhere for a second opinion.

If you can provide the information the OP did not, we might be able to help you.


You need to do the same as we asked him to do. The more information you provide, the closer we'll be to your solution.

Or, as Andrew said, you could continue to throw parts at it until you get lucky.

Regards, Norm