2003 Mazda MPV - mechanic stumped

I have been struggling with my vehicle now for several weeks. I have had two ignition coils replaced and the TPS, which the vehicle was throwing codes for. I got it back from the shop, but it still hesitates very badly. It is not going into limp mode anymore, nor are any new codes coming up. It consistently stutters at highway speeds, and especially going uphill. Fuel economy is horrible. The mechanic said he could change the rest of the plugs and coils, but without a code doesn’t know that the 400-500 dollar fix would solve the problem, and wouldn’t recommend it. Are there other things that they may have overlooked that would cause this that would not cause an error code? I was basically told to drive it until the check engine light came on so they would know where to start.

Have them check the coolant temp sensor for the computer.

The CTS is one of the primary inputs into the computer. If this sensor is sending an erroneous signal to the computer, telling the computer that the engine is always cold when the engine is actually at operating temperature, it’ll cause poor performance from the engine and poor fuel economy.

As long as the sensor is sending a signal to the computer even though it’s erroneous, the computer thinks the signal is valid and the Check Engine light doesn’t come on.


Are you going to an independent service provider or a dealership ?

Independent provider. The only Mazda dealer is 45 miles away.

Depending on the actual speed when the “stuttering” occurs, it is possible that you are experiencing problems with the transmission’s torque converter lockup mechanism, and that this is not an engine problem.

At what speed does this happen when driving on a flat surface?
Is this simultaneous to the downshifting of the transmission when you are climbing a hill?

There’s a lot of things that can cause a stutter and not set a code; engine mechanical fault due to compression, vacuum leak, low fuel pressure, iffy MAF sensor, iffy crank sensor, EGR pintle stuck open, clogged converter, iffy spark plug, etc, etc. The list can be lengthy and things are not etched in stone.

You refer to “the rest of the plugs…” which I assume to mean the mechanic changed the plugs on the cylinders that got the new coils and did not on the untouched cylinders.

Just my 2 cents, but I would never consider doing a partial plug change. It’s all of them at the same time and preferably a compression test while the plugs are out to weed out a mechanical fault. Maybe this stutter is simply an unchanged spark plug and which could be the reason for the coil failures.

He said they pulled the plugs out on the coils they changed and they looked OK, so I guess it was more a matter of checking the plugs. In this vehicle, you have to take the manifold off to get to the back three plugs, so they were not checked.

It stutters slightly at low speeds, and fairly intermittently. Once hitting highway speeds of 55+, it is almost constant. I guess the best way to describe it would be that the engine feels like it’s “choking”.

I did have issues starting it yesterday, but it was in the negatives and some time hooked up to the battery charger and repeated cranks got it started.

If he didn’t pull the rear plugs, he’s guessing they are ok. Also, he’s guessing the rear coils are ok. This guy is a clown. Check the mechanics files link for another mechanic in your area.

It can be near impossible to eyeball spark plugs out of modern car and determine whether or not they’re misfiring to some degree.

Maybe those plugs he said looked ok are not so much ok.