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I have a 96 Mystique 2.0 MTX. It has severe hesitation issues under load. Basically if I floor it it chugs hesitates and bogs down.

I have replaced both O2's
Replaced the wires.
Replaced the plugs
replaced the MAF
replaced the DPFE
Checked for vaccuum leaks.

Still the problem remains. I am starting to think it is the TPS. Does this seem logical at this point. I have ruled out the fuel pump as this issue doesn't exsist on a fresh start of the engine. However it shows up when it is out of the loop mode. Any other idea aside from the TPS? I have searched but more often then not people with this similar problem never post what the ultimate solution was for them.

TIA

I would suggest a new air and fuel filter and a TB cleaning. In addition, check to see if the catalytic converter is plugged.

So you don't feel that the TPS could be the culprit? I should mention that if I am in nuetral and I raise the RPMs slowly @ about 1500-2000 there is a most pronounced stumble. Addingg to my suspision. As for the filter I have a conical filter that is relatively clean. As for the fuel filter. It was done not to long ago.

Originally posted by mbb41:
So you don't feel that the TPS could be the culprit? ..

It could be but TB cleaning is cheaper (as a first check) and I think a TPS issue should show a CEL code. Of course, a really dirty TB would too). Do the plugged exhaust test too. Oh and read the recent post by Edmonton on problems with the Zetec too.

Edit. "Anyone know if it could be a clogged cat or how to test?"
For the Zetec.
A good cheap way to test for a blocked exhaust is to remove the upper O2 sensor, and see if the performance improves. Battery needs to be disconnected before uninstalling and installing O2 sensors. Good luck.

Be easy enough to test the TPS theory. Un-plug the thing & run your car for a while. If it seems to run ok, Ta-Da!!

If that doesn't work, try un-plugging the MAF instead and then run your car for a while. If the car seems to run fine, then Ta-Da!! Your MAF was the problem.

Originally posted by TourDeForce:
Be easy enough to test the TPS theory. Un-plug the thing & run your car for a while. If it seems to run ok, Ta-Da!!

If that doesn't work, try un-plugging the MAF instead and then run your car for a while. If the car seems to run fine, then Ta-Da!! Your MAF was the problem.

Hmm.... shoudn't that be "unplug it and if there is no difference in the performance, that component is the problem"?

TourDeForce

Yours was one of the post I found with no difinative results on what the problem was that you had. Ever figure out what was up? I was planning to test your theroy tonight after I pick up my car from its E-test. (which I just found out it passed no problem) I am going to unplug it and drive and see what happens. This won't screw anything up I hope. I do not recall right I'm sure but I thought the car won't even run if the MAF is unplugged.

Originally posted by Tony2005:

Hmm.... shoudn't that be "unplug it and if there is no difference in the performance, that component is the problem"?

Why would that be the case for certian? I assume by doing this you have the car go into limp mode for the missing sensor. Therefore it will run @ default trim. If that is the case then the car should run better then with a sensor that is running right intermitently no?

Unplug MAF:

The car will run off the stored fuel trim tables with added data from the other sensors such as TPS, O2s, etc.

So, if the MAF is having a problem, your car will run like crap. Unplug the MAF & your car will run fine with no drivability problems, but maybe pull some timing or give you a richer fuel mixture.

Should be the same for the TPS.

Originally posted by mbb41:

Originally posted by Tony2005:

Hmm.... shoudn't that be "unplug it and if there is no difference in the performance, that component is the problem"?

Why would that be the case for certian? I assume by doing this you have the car go into limp mode for the missing sensor. Therefore it will run @ default trim. If that is the case then the car should run better then with a sensor that is running right intermitently no?

Wouldn't it already be running in a limp mode if the component was the problem? So if you remove the component, it shouldn't make any difference whereas if it wasn't in a limp mode for that component, it would now, if you unplug it. Maybe someone else with more experience with the mechanics of the PCM could clarify this.

have you reset the computer after changing all of those items?

also when you talk about a stumble off idle that sounds like the plug wires, as this it what happened to me once. we thought it could have been the tps sensor also. my car was stumbling and chugging off idle to near 3 to 4k rpm. could be a bad wire or spark plug.

I would say if you have your old wires try swapping one out at a time to see if that will do anything.

I put brand new wires on that I know for a fact were good as they were tested on another vehicle.

Originally posted by Tony2005:

Originally posted by mbb41:

Originally posted by Tony2005:

Hmm.... shoudn't that be "unplug it and if there is no difference in the performance, that component is the problem"?

Why would that be the case for certian? I assume by doing this you have the car go into limp mode for the missing sensor. Therefore it will run @ default trim. If that is the case then the car should run better then with a sensor that is running right intermitently no?

Wouldn't it already be running in a limp mode if the component was the problem? So if you remove the component, it shouldn't make any difference whereas if it wasn't in a limp mode for that component, it would now, if you unplug it. Maybe someone else with more experience with the mechanics of the PCM could clarify this.

Anytime the PCM's expected values from any sensor (maf, TPS, o2, etc) are above or below a maximum range, it will use a failsafe table of values instead of relying on that sensor.

If the removed problem sensor is already operating beyond its ranges, then the car would be relying on those tables already... Of course... it would usually throw a CEL light/code as well..

Ray

Well I pulled the wire off the sensor and heres the results.

The car never threw a CEL. The problem however remained and infact was more pronounced. Basically this actioned intensified the problem. However the stumbling issue when reving lightly in neutral went away. I assume because the mixture was richened up. Cost for a new TPS is $33 so I'm inclinded to change it anyways. I am however confused as wether this is the ultimate problem or not. Given the problem didn't go away with the sensor detached and the computer restarted. More odd to me that no codes were throwen.

test the tps with koeo.

4.7v(i THINK.. it's early) at WOT

around 1 volt at idle.
look for smooth transitions, as well, while revving via the TB.

When was the last time you checked/changed the timing belt?

Did you try un-plugging the MAF?? If you replaced the maf recently, it could end up being a wiring issue.

Well the timing belt is about 75000 miles so it could be done I'm sure. I had the same thought but unless it is slipping or something and then going right back to the right spot I'm not sure that it could be it. As far as it being a wiring issue I realy hope that is not it. The E-test I had passed with flying colours. Nothing really stood out.

That's right, you said it runs ok on cold startup....

That leave un-plugging the MAF for now. An easy & free test.

Well I will give that another shot I suppose. I have swapped a maf before and it seemed to make no difference.

Have you ever changed the PCV valve? Apparently, that can cause stumbling too.

http://www.contour.org/ubbthreads/showflat.php?Cat=&Board=zetecmaint&Number=982031&Forum=zetecmaint&Words=pcv&Match=Entire%20Phrase&Searchpage=0&Limit=25&Old=allposts&Main=982031&Search=true#Post982031