02 Protege with Rough/Dying Idle and P0302 + P0171 Codes

Mazda, Protege DX
Hello everyone,

My father and I recently replaced the head gasket on my 2002 Mazda Protege DX (2.0L Engine). Since then, I have had a rough idle that I simply cannot get rid of. The car only has problems when at a complete stop or crawl speed (like moving up a car length in an intersection). When it is actually driving it runs smooth as can be, highway and backroads. The odd thing is that the car runs only slightly rough right after start up (when the engine is cold) and progresses to where it bogs out and dies/almost dies after the engine has warmed up. After the car is actually driven for any length of time, it has a fairly violent idle and dies within 30 seconds of stopping.

At first the idle was very rough and throwing only a P0300 code (Random Misfire). My dad and I tried many things to fix it including:
Replacing all coil packs and wires
Replacing all spark plugs
Replacing the EGR Valve
Replacing the PVC Valve
Replacing the IAC Censor
Cleaning the MAF Censor
Spraying throttle body cleaner around the intake manifold to check for leaks. (The engine did not rev, so we're guessing there's no intake leak.)

After doing all of this, nothing was fixed, but we did find that running the A/C made the car run smoother. My father also adjusted the idle up just a little bit. (Which I later read is not supposed to be messed with. (doh) ) It still had a rough idle, but was not at the point of dying, so I went with it.

Now after a week or so, the idle has gone back to almost dying, even with the A/C on. I did another OBD-II scan of the Check Engine light and now it it is throwing a P0302 code (Misfire in the 2nd cylinder) and P0171 (Engine Running Lean). We're now thinking that the fuel injectors may be the issue, but after a quick test (putting a screwdriver up to the injector and our ear to the other end.) It sounds like all for injectors are firing at a constant rate. So we're not sure there.

I am so frustrated and low on funds that I can't keep throwing money at the car if it's not going to fix it. :( The mechanics we've spoken too are pretty puzzled too and told us they'd be doing nothing more than guessing fixes too, and I can't pay them to guess, lol.

I didn't know if anyone on here had any advice on what to check next. Obviously with the head gasket repair, we took most of the engine apart to get to the head, so it could be a number of things wrong. We do however know that the head gasket was installed correctly, because there is no longer air bubbles in the coolant and the car does not overheat. So we do not believe that the misfire is due to the head gasket. Also I'll note that the actual problem with the "head gasket" was that the head was warped. An engine shop we took it to milled 8 thousandths off the head to get it flat again.

If any more info is needed, please let me know. Sorry this is so long, I wanted to be thorough since we've done quite a bit to the car already. Thanks!
2014 Mazda3 S GT auto, 2008 MX5 6-speed
Does it idle okay if you throw the transmission into neutral? If so, check the auto transmission fluid level (while in Park or neutral and after the engine is warmed up)?

I had a similar problem with my MX6 GT. Once I brought the trans fluid to proper level on the dip stick, the smooth idle returned and all was well. Apparently, one of the valves wasn't functioning properly with low fluid, and the trans wasn't shifting into first gear.
Mazda, Protege DX
No, it's less noticeable from inside the car when it's in neutral, but the engine does not behave any different.
Mazda, Protege DX
I've already checked the big intake hose. (Actually had it replaced less than a year ago, so it should be good.) I haven't checked the brake booster hose though, I'll have a look at that tomorrow.
Did you get this resolved? I'm in the same boat with a 2002 Protege. Have done everything you mentioned and no luck. Mine is a little different in that it idles smooth with a/c off, then sputters with a/c on. Also smooth in Park, same sputter in gear. I've also let it idle with the pcv valve both plugged in and not, no difference. Same with the EGR connected and not. Did the same with IAC. It won't idle by itself when disconnected, but I can hold it at idle speed with the gas pedal and all the symptoms exist. At my wit's end.
03 Protege LX
I'm sure the car is either gone by now, or been fixed. However I just did my head gasket, valve stem seals, timing belt, water pump, and after assembly ended with the same problem. Ensure that the intake manifold gasket has been installed properly and creates a tight seal. That fixed my problem.

Sent from my VS986 using Tapatalk
2003.5 MAZDASPEED Protege #2218
has anyone found the fix to these problems?
I recently bought a 2003.5MSP with the same issues and throwing
the same codes P0302 & P0171.
part store ran a list of 15 parts that could fix it... but I don't wanna replace parts not needed.

Latest posts