Rough Idle/Low RPM's
 

Hi all,

I'm having some trouble with my 95 Protege with respect to the idle. When I start the car in the mornings, the RPM is high(normal IMO) and as I continue to drive and the engine heats up, the RPM drops to around 400 or so. This happens mainly when I come to stop(throw it in neutral...its a 5 spd).

Also, after driving for a little while, park the car, go to the store, get back into it and fire her up, the RPM is around 300-400. It's unusual because I never had that problem before.

Any Ideas?

you have a dx or lx with the 1.5? are you running the ac compressor. that'll do it. if not, it's happened to me..well still occasionally does. someone here said this is kind of a quirk/characteristic of the cars. did you try searching the forum, it may have been covered before in vastly more detail than my "it happens and that's kind of a 1.5 thing" explanation.

i did a search. this discussion could give you more tangible ideas/possibilities of action:

https://www.mazda3club.com/showthrea...=1.5l+low+idle

thanks, but its a 1.8L DOHC, LX.

k, so I noticed a crack in the hose connected from the air filter to the engine block....just wondering if that would cause it?

Thoughts?

hmm, PCV valve hose...i don't know if the engine relies on a calculated amount of air from there or not. possibly. i hope there's nothing clogged or messed up around the throttle body. wonder if there's a vacuum leak still...

anyone else with more know-how please feel free to jump in here. have you tried other forums and searches on those forums? maybe they'd have something more there just because they are more heavily populated.

Leaking air boot (the cracked hose) can DEFINITELY screw up idle.

The MAF sensor to the intake side of this boot very precisely measures the amount of air coming in. The computer meters fuel to the engine based on this measured air flow. An air leak downstream of the MAF sensor means this calculation is wrong and the air/fuel ratio will be wrong. A small leak won't be noticable except at idle, when the amount of air and fuel is pretty small. Fuel economy might suffer.

Replace the boot before doing anything else. About $35 online.

so I replaced the hose(with one similar...I may have to go to the dealership to get the exact hose, but there is one in place temporarily that's a tight fit, however the hose is sorta kinked...I will look into the correct hose as soon as I can....)

I also changed the PCV Valve...thus far, haven't really noticed much different other than upon acceleration, the car appears to have more power now....HOWEVER...the idle still drops at a stop.

Any other thoughts?

- any vacum leaks can screw up idle. look and listen for leaks. you can buy a vacum tester but I don't have any experience
- repeating myself, but any intake air leaks downstream from the MAF will screw up idle
- EGR malfunction
- sticky EGR valve. pull it off and clean it. search and you'll find diy howto
- plugged EGR vacum port. unplug the vacum line above the EGR valve and see if the port is plugged with carbon deposits.
- dirty MAF sensor. buy some MAF Sensor cleaner (electrical circuit cleaner will work). remove the sensor and spray the crap out of the two wires buried inside. DON'T TOUCH THE WIRES WITH ANYTHING. not even q-tips.

If you search the various mazda/protege/323 forums, you will find DIY instructions for everything I've listed above, now that you know what to look for.

I also saw somewhere that a faulty clutch switch could cause idle problems. If you think this might be it... there are two switches on the clutch, I think it's the one NOT on the firewall.

a picture would be nice; not sure if we're talking about the same part.

anything that changes airflow between the MAF and the throttle body will screw up idle.

okay, here are some pictures...

Okay. A leak in that hose could cause idle problems.

EGR is on the side of the engine closest to the firewall. I'd guess it's about 8 inches below the top of the engine - that's a guess cause I'm at work. At least on my 1.6 it's there. It's kind of a pain to get your hands back there to remove it. I've got big hands, tore up my knuckle, and could only move the ratchet about 3 clicks each time.

There is a howto I think on the protege323 forum, probably elsewhere. Tells how to take it off, take it apart, and clean it. You could also just buy a new one but they aren't cheap - and if it's not the problem you wasted the $.

okay, so that's the hose I replaced...its not perfectly "bent" in the proper shape but its doing the job.

I've reviewed a how to on how to clean the EGR but I'm kinda nervous and don't want to screw it up...its a 1995, and I can only imagine how seized the bolts etc would be...with that said, I'm not afraid to get my hands dirty so I'd tackle it... A new one costs upwards of $200...priced it out already.

As for the location, I'm not exactly sure where it is....I think my red arrow in the pic is where its located but I'm not sure...

Also, I was wondering if I did get it out, what I would use to clean the inside...what's a good carbon cleaner? Would brake fluid suffice?

I used brake cleaner, on advise of the DIY. I'd say it worked ok but not great. I ended manually scraping carbon deposits from the EGR valve plunger. You might ask the guys at the auto store.

First pic shows overall location (green line)

Second pic shows the top of the EGR valve (green circle) and where the vacum line connects (red arrow). The EGR valve comes off with two bolts, 14mm I think. Then it comes apart and you'll be able to tell if it's sticking by moving it manually.

Remove the vacum line, and make sure the port's not plugged. Mine was plugged and I cleared it out with a small dowel. I heard somebody else say they had to use a drill.

Just found the exact same cracking on my wifes car.
Its been starting fine, idle great but won't accelerate properly.
I knew it was running a bit lean but couldn't find any vacuum leaks until today.
I think that at idle there wasn't enough vacuum (and revving it stationary didn't load engine mounts?)
When driving, the movement must have been enough to cause air leak on bottom of intake 'bellows'?
PJ