Jerky Festiva

[tybled17]

I have a 91 Festiva, 5 speed, 153,000 miles. Best car I've ever had!! I've had it since 92. Last week she started running rough and the engine lught came on, I changed the plugs, wires, cap, rotor, fuel filter and 1 injector that was not spraying. I also removed other injectors and cleaned them and replace each of their O rings. I was going to change the O2 sensor but the old origional one was rusted in place and I'm sure it would snap off if forced. Now, she starts fine and picks up speed fine, but when you reach your speed and let off the throttle (just enough to maintain speed), she jerks like she has bad gas or something, the exhaust has a miss in it and the engine light stays on. I ran 2 bottles of dry gas through her, but no luck. I seem to think it may be a sensor or something and can't figure out how to get the engine codes. So for now' she rests quietly in the garage. I'm at a loss!!! I'm forced to drive my F150 which gets 11 mpg and I'm going broke for gas... Thanks for any input,
Ty in Maryland

[elcamino1]

you have never changed your O2 sensor since 92.may be cause of your problem

[packrat427]

It could be you TPS (throttle position sensor) located on the side of the throttle body , little black box on the opposite side of the throttle cable .

If it is out of adjustment ,it will act like that .
Have you tried cleaning the throttle plate in the throttle body itself .

[tybled17]

I had the throttle body off yesterday and cleaned it real good - no luck. I don't know how to get the O2 sensor out without it breaking off since its origional and rusted itself to the manifold. As far as the TPS, any idea how much$, and is that a dealer item or shelf item? Thanks for the replies, I hope to get her running by this weekend. Ty

[packrat427]

It may not need replaced, it might just need to be adjusted .

If you want to replace it , they have them at most part stores .But it will still need to be adjusted , after you replace it .

As for the O2 , soak it real good with PB Blaster for several days , then get a socket that is specifically designed for the O2 sensor .

Run the motor a little and get it hot spray it , hot and cold so it will penetrate good .

[tybled17]

You say it may need adjusted, you mean the TPS? How do you adjust them? I tried the trick with the PBblaster, heat and 02 socket and still won't budge, matter of fact, I broke a breaker bar in the process. I was looking through the site and found someone else had the same problem that I'm experiencing but I think he explains better than myself, ("causes to trigger check engine light" posting in repair forum), but with a carb'd 88, someone told him to check the EGR valve. Do I have an EGR on my FI festy? Thanks, Ty

[packrat427]

Do you have a repair manual , You need a volt meter to do it correctly . I moved mine just a little and my very similar problem went away .
Yes the black box (TPS)

[tybled17]

Yea, I have a manual, covers Festy's and aspires. I will check it out Wed. to see if it covers the adjustment. Question though, exactly "what" do you adjust, are there settings inside the TPS? Where are the adjustments performed at? Thanks, Ty BTW: What is this "Sea Foam" I'm reading about for cleaning the engines internally? I appreciate your replies!!!

[packrat427]

Seafoam is great stuff , it will de-carbonize the combustion chamber , valves , intake .
You can use it in you oil, gas , or pour it directly into the intake , or thru a vac line . search that ..Seafoam , look for the video I made , and the other post and you can see a variety of ways to use it .

The TPS , little black box has elongated holes , and can be moved up, down , back and forth , the box itself , search that too , I noted all the voltage readings that is supposed to be at idle , part throttle , half and full , the readings change .

[WmWatt]

What is the code from the check engine light?
Did't see it in the dialogue.

[Roys1955]

Take the rubber hose off that goes from the mass air flow sencer to the throttle body and take a GOOD look at it. Mine had a small crack in the rubber that would open up and let air in, gave me all kinds of trouble. Looked at it from the top and it looked new, the small crack in the rubber was at the bottom in between the corrigations, hard to find untill I took it off and bent it back and forth. Replaced it and now she runs as good as new, she has 150000 on it.

[bsirvine]

If you just can't get the O2 sensor loose, take it to a repair place that works on a flat rate out of the flat rate manual. If they break it off then they have to eat the cost of getting it out and putting the new one in. Kind of nasty, but I guess you gotta do what you gotta do.

[Bowls]

I had to fix my gas tank lock, which was 1 solid piece of rust when i bought the car. soak ur o2 sensor with oil for a good few hours, keep applying. scrape it clean with a screwdriver n toothbrush, and then u might be able to see where you need to take it off from.