I just purchased an 03 Protege 5 and everytime I'am cruising between 50-65 i get Check Engine Light and I disconnect the negative battery terminal for 20 seconds turn the car on and no check engine light. it only happens in the highway not during city driving just weird.

 

did you check to see if the recall for the intake manifold was done on your car? mine did that to and i found the recall went and had it replaced did fine for awhile till the screws ended up in the precat

 

Random misfires MEANS random misfires, nothing else. Misfiring is detected right on the coil primary circuits and has NOTHING to do with air intake, EGR, fuel pressure etc. etc. It's purely the electrics.
I've got a '99 Protege in Canada where they turn snow into slush by dumping heaps of salt on it. My coil packs and ignition wires are right up front where they get covered with this s**t.
Here's what I did at 90,000 Km. (60,000 mi.). I replaced the high tension wire harness with an OEM kit which includes the plastic spreaders, standoff mounting posts, and plastic spiral wrap. IT IS VERY IMPORTANT that NONE of this wiring can touch anything metal !
I cleaned the coil packs thoroughly and I unplugged the primary connector sets (the 3 wire plugs at the front of the packs) and gave both plug and socket assemblies a thorough soaking with a contact cleaner aerosol. Result ? No more misfiring.
When winter's gone I'm going to make a sheet metal or plastic deflector plate and attach it to the coil pack mounting bracket so the s**t coming through the grill is deflected upward and rearward of the high tension area altogether.
Years ago, when the very first British mini's appeared, they had a Lucas ignition system with everything, including distributor, mounted up front too. Between this and the tiny front wheels it meant that if you didn't slow right down for puddles, you could bet big money that the car would stop dead within 100 yards or so of the encounter.

 

Lots of confusion here. First, a P0300 code is the HEATER of the upstream O2 sensor, not the sensor element itself.
Suggest you look carefully at the connector and wiring to your front O2 sensor, i.e. the one nearest the engine, before considering sensor replacement.
Second, a misfire code is electrical ignition voltage only; nothing to do with air, fuel, exhaust etc. etc.--- just wiring, insulation and connectors.
Finally, a P0171 is idle fuel trim out of range. By far and away the most common cause for this is deteriorated plumbing of the air intake ducting downstream of the MAF sensor (the little box just behind where the air from the filter joins the ducting going to the engine). Cracks in this ducting can be hard to see and usually are located at the engine end of the duct. You have to wiggle the ducting around to locate the problem. Proteges are notoriously prone to this. A diagnosis can be easily confirmed and a temporary fix made with just some insulating tape as a bandage.
Symptoms of this problem are unstable idle speed, stalling at lights etc. in the low speed/ low load spectrum. Under cruising conditions there are no apparent symptoms.

 

This OBDII code represents random misfire. A P030x code (with x representing a cylinder number) indicates that a specific cylinder is misfiring. The P030x codes are triggered by a software routine that checks for incomplete combustion in a cylinder. This code is usually, but not always, caused by lack of spark on the compression stroke. If the engine control computer cannot detect which specific cylinder misfired, it then returns the generic P0300 code. This means that multiple cylinders have experienced a misfire condition -- as opposed to any one, single cylinder.

Here are links to websites that explain this code in further detail:

http://www.obd-codes.com/p0300

http://www.engine-light-help.com/P03...ine-light.html

 

My apologies re the front O2 heater OBD code issue. I was looking at P0030, not P0300, NightSwimmer's absolutely right.

http://www.obd-codes.com/trouble_codes/ is another good OBD site too, and has general and manufacturer specific codes, plus guides to probable causes for some of the codes.

This is by way of a question:
Would a slipped timing belt result in the general misfire code ?
This implies that the ECC is looking for spark within a permitted range of angles before TDC and if spark is not "seen" in that time frame, a misfire is flagged.
This would be consistent with the ECC not being specific about which cylinder/ bank is out, because all of them would be.
Incidentally, if the engine is not firing correctly, unburned fuel delivered in the exhaust is burned in the catalytic converter and can overheat it and rear O2 sensor which over time damages both.
A couple of "rustic tricks" for misfire detection are a) run the engine in the dark and see if there are sparks jumping off the wiring or coil packs anywhere. b) get a crappy little radio with an AM band on it, tune it where there's no station, and listen to the ignition noise. A smooth zippering sound indicates ignition OK, and a loud rough irregular rasping sound means not OK. b) has the advantage that you can put the receiver beside you while driving.
The normal car radio on AM band might be OK too, but some (like mine) are so well designed and filtered that the ignition noise is too suppressed, or else they won't stay tuned on a frequency that does have a station.

 

wow look at all the answers all of the sudden ...
and sorry I should have explained better I did get a random misfire code before I had the intake replaced my sparkplugs were actually being bent thus misfire (least thats the way it was explained by mazda) anyway the sputtering and everyhting else occurred to thats why I asked if you had checked just to make sure

 

Do you mean to say that changing your intake manifold resulted in screws making their way into your catalytic converter?

This couldn't happen unless they traveled through your engine and your exhaust manifold along the way -- could it? I think that I would insist on a new engine if this happened to me.

Just Sayin....

 

If trouble points to the EGR valve, check the tubing associated with it. It's not uncommon to have an accumulation of oily residue in there which fouls the EGR and obstructs the flow as well. You need to ream the tubing out to clear it. This could save you the price of the EGR valve.

 

The MAF (mass airflow sensor) where is it located on the Protege 5?