Help! No one can figure out what is wrong with my car!

So I have a 2003 mazda mpv and i will try to explain what is wrong with it… while driving, idling, backing up it intermittently jumps or hesitates or shudders. it will sometimes stop the “shuddering” if i turn the air conditioning off. the first time we brought it to the mechanic they said a tune-up ($360)…it was fine for about 2 days and then it started again. so they change some gaskets - it was ok for about a day and it started again. i think we took it there once more and i can’t remember what they did but it didn’t work. so we took it to another place - they couldn’t even tell that anything was wrong with it (i guess because it doesn’t do it all the time??) so they did an emissions flush. it has been a little better but it is slowly starting the jumping, hesitating, shuddering (whatever you wanna call it) again. like i said the air conditioning seems to make it worse. it’s not stalling or anything. my guess is something is wrong that is clogging up the works and it clears out when they mess with it but they aren’t fixing the real problem. we only have one car so it is a huge headache to leave it somewhere. any help would be great!! thanks!!

oh and when the problem initially started the check engine light came on - after the tune up it went off.

It could be a bunch of things but that check engine light being on means that there’s an error code stored in the computer for you to retrieve, unless whomever tuned your car up reset it. Knowing what that code is will help us help you. Go to a place like Peboys or Advance Auto and have them read your code. They’ll do it for free in the hope you let them fix it. Politely refuse and post that code here.

Btw, when you say it stumbles, is that at all speeds or just lower speeds? Does it only do it when you have the AC on?

Never heard of an emission flush, btw. Do you mean ‘transmission flush’?

One Long Shot To Check:
Check The ECT (Engine Coolant Temperature) Sensor For Cracks On The Brass Housing And/Or Check The Sensor Operating Resistance Against Specifications. Some 2002 - 2005 MPVs Have Been Found With Faulty ECTs That Can Cause Rough Running And Hard Starting.

Coolant can get inside these faulty sensors and the temperature of the ECT is sensed as too low even though the vehicle is at normal operating temperature.

See if you can get a DTC (Diagnostic Trouble Code) as RemcoW has suggested. That could take a lot of wild guesses out of this problem.


the check engine light isn’t on anymore. the auto store said they can only do it if the light is on…

Go back to the beginning. Before any work was done, how often did car shake? Every time you drove it or every few days? It would be ok for 1hr but than start to shake? So, they worked on car, did the frequency of ough running drop a lot or a little? You said they workd on it and it ran fine for a few days? Completely fined. No shaking for several days?

before we had it fixed it never did it - i was on my way to work and the check engine light came on when it started doing it. i came home and got my mom’s car because i didn’t think it was driveable (felt like it was going to stall). this last time it got fixed (the emissions flush) it worked completely fine for i would say 3 days before small “hiccups” started. it still isn’t as bad as when it was at its worse (which was after we brought it to the 1st place and they put on new gaskets). sorry it’s so confusing - it is a weird problem i guess… thanks for everyone’s input so far!!

Taking a stab at it, I figured there’s a possibility of it being the Idle Air Control (IAC) valve. That’s why I asked the question regarding when it happens (what speed, AC on, etc).
In looking for a picture of that device, an article came up describing almost the problem you’re having.
Locate that device under your hood and tap it slightly with something like the heavy end of a screw driver. See if the idle changes. That could buy you a clue.

I am going to speculate (due to previous experience) that the problem may be happening because of a wiring issue within the engine area, possibly a faulty ground. That can cause all kinds of problems like this. Since turning off the AC can sometimes make a change for the better it may be because the current load for the AC compressor is removed. If there is a faulty ground that would tend to make things better due to a lesser load which translates to less voltage drop across the bad connection. That then tends to let other things work better as they now get more power provided to them. Cleaning the battery connections and checking the alternator connections would be a good thing to do also along with cleaning the engine grounds.

@RemcoW, I love to use the screwdriver trick to find intermittent troubles. As you know, it works very well at finding gremlins within the electrical system.

If it happens only while the ac is on I like @remcoW