TPS? Or other issues?

[SilverGGA]

Hi, I have a 2005 Mazda 6i automatic (4-speed).

I was on my way from LA to SF driving at ~70-79 mph on I-5. Weather was really hot at ~95-100F. At about the mid-point of my drive, the car got really jerky when I let off or got back on the throttle, so I took the closest exit and proceeded to a gas station. As the car was rolling to a stop, I needed to step on the gas "really" hard to make a full stop. As I was stepping on the brakes, I also heard strange noises similar to brake torquing an ATX car.

I then put the auto to neutral, and RPM would fluctuate between 2-3k RPM.

Popped the hood and everything was really hot, due to the weather I assumed. But all fluid levels' were normal.

I then shut the car off, kept the hood open for ~10 min to cool down, and restarted. Everything was fine for the second half of my drive.

CEL did not come up, but I did not have a reader to check if there were hidden codes.

Does this sound like TPS failure?

This is my wife's car and she's pregnant. I am debating whether I should try to fix it (replace TPS, clean MAF & throttle body), or replace the car (the 6i has 120k miles now).

Oh and the car has synthetic all its life. I only use top-tier gas and it gets a bottle of Techron concentrate every oil change (7.5k miles).

Also recently replaced spark plugs, serpentine belt/tensioner/pulley/water pump, thermostat, air filter, coolant, brake fluid, brake pads, ATF and power steering fluid. All were OEM parts and I had my mechanic to do it since I was lazy.

I am taking it back to have the mechanic look at, but would like to get some ideas from here first...

Thanks!

 

[StevieC]

Being that the engine was lugging and then the rpms were erratic I would speculate that the MAF might be dirty or starting to flake out or it was the Idle Control Motor sticking.

TPS wouldn't cause this sort of problem.

 

[willix]

I could be the TPS, I would suspect the cam sensor or crank sensor. It sounds like you used up the vacuum reserve for the brakes. A TPS will usually cause erratic idleing or a dead spot in the pedal movment. I suppose it could cause a shifting issue in the trans. Jerking could be sensor is momentarily losing its signal to the computer and may be cutting off & on the fuel or ignition. Maybe quickly enough that the ECU isn't recording a fault. It may be as simple as a faulty connector. You really need to get codes to see if there is a history. Many things can cause this water or oil fouled spark plug wells may cause this.

 

[ItsuMitsubishi]

Silver, was the idle fluctuation a steady rhythm like a rev limiter? The brake torquing thing sounds like the throttle or IAC like Stevie mentioned, might be sticking or failing. If indeed the RPMs are fluctuating 2-3K rhythmically, indicates that the ECU is using a crude backup rev limit. It would do this if the throttle oe IAD was sticking open a bit, but it detected 0% pedal application, or in older cars the idle switch was closed. Some of the older MAP cars did this like old Accords mostly from what I've seen. Because they are MAP systems, any intake manifold leak or vacuum hose would simulate some throttle, but the idle switch was closed, causing the engine to hard limit the RPMs with fuel cut. Your car uses a MAF, which could really narrow the problem to some part of the throttle body; either the plate, servo or IAC. It wouldnt hurt to clean the MAF also

 

[mechtech2]

Check it for codes. There may not be a dash light, although there should be if there is a problem.

BTW, if you have to step on the gas very hard to make a stop, this is quite normal! Less gas would make for easier stops.

 

[SilverGGA]

Originally Posted By: mechtech2
Check it for codes. There may not be a dash light, although there should be if there is a problem.

BTW, if you have to step on the gas very hard to make a stop, this is quite normal! Less gas would make for easier stops.


Sorry I meant I needed to step on the brakes really hard to stop. Like something is fighting against the brakes. Makes sense if the engine is at 2-3k RPM...