Out of ideas for random idle dip, almost stalling!

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devinw

Member
:
02 Protoge5
OK, ya'll. I'm starting to get to the end of the rope here on figuring out my idle dip problem. The car runs fine except when ideling it will dip randomly (say usually 1 or 2 times during a typical traffic light wait) down to 200RPM or so and pop right back up to 700. It dips so low that it sounds like it will ALMOST stall but never does. Here's all the things I have done so far, and none have had a single bit of impact on the problem:

-Clean MAF
-New coil packs
-New spark wires
-New spark plugs
-New air filter
-Replaced intake air tube (was throwing a lean mixture code... this fixed it! But.. idle problem didn't change)
-Replaced EGR valve
-Ensure EGR tube is clean and clear, as well as passes in the intake.
-Replaced IACV and had cleaned passages in the throttle body while it was off.
-Replaced PCV valve
-Visually inspected all vacuum tubes. Replaced one of that that looked a little brittle but wasn't cracked.

I just don't know what else to do here! It just seems crazy to me. No codes getting thrown. Car runs fine, but it just won't idle right. WTF?!
 
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I need to locate the EGR tube and clean it out myself. where exactly is it as I've never cleaned it before?

any chance there's a diagram of all the vacuum lines? I'm having the same problems after getting the head redone. replaced the egr and did some more maintenance. if you look at my posts you'll see what I'm talking about.
 
johnnyphive said:
I need to locate the EGR tube and clean it out myself. where exactly is it as I've never cleaned it before?

any chance there's a diagram of all the vacuum lines? I'm having the same problems after getting the head redone. replaced the egr and did some more maintenance. if you look at my posts you'll see what I'm talking about.
Click to expand...

The EGR tube comes off the side of the exhaust manifold and goes under the throttle body. If you have the throttle body off it's easy to see. Both ends have a 26mm nut on them which I would recommend spraying with PB blaster to loosen up. I was only able to crack the manifold side one free, but this allowed me to spray compressed air through it and see it was free and clean to the intake manifold side. The intake manifold side nut was ungodly tight and in an awkward location so I just gave up on completely removing the tube for fear of breaking it.
 
Well... Here's the big list...

I'm personally gonna go with partially clogged injectors.

I know you've heard me say this before, but I think you should throw half a can of Seafoam in the gas tank and then add a shot every time you fill up.
It's cheap and easy and worth a try.

Keep in mind that the ECU and IAC need to relearn how to idle your car every time the battery is disconnected.
My car does it too after an ECU reset... Very close to stalling.

It takes about 100 miles with different engine temperatures and such.

Screenshot_2017-11-20-12-23-25.png
 
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Haven't tried the Sea Foam yet but I did run a whole bottle of 3M fuel system cleaner in the tank.

Since this is my wife's DD, I just had her take to a shop this morning. Will report back if they find anything. THis has been super frustrating though. I've never had a car with as touchy an idle as this. I'm used to Hondas lol. Never had a bad idle on a Honda, even with ones with 250k+ on the ODO.
 
Same, my idle has been as low as yours but never goes up and it feels like it's close to stalling. You can see the needle flutter as well, ever soo slightly.
 
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That fuel treatment should have cleaned things up.

The way you describe the bouncing idle sounds exactly like my car when it's relearning to idle.
700 rpms, then the ECU hands over control to the IAC and it fails it's attempt to idle, so the ECU takes back control, brings the RPM back to 700 then tries to hand back control to the IAC again... learning from the other attempts.
My idle wouldn't drop as far with each attempt, until the idle stabilized at 700 RPM.

Your car may simply need some time to figure things out with a bunch of idle attempts at different engine temperatures and other conditions.
 
there was an issue similar to this years ago. the butterfly valves inside the intake manifold had come apart and were banging around inside of the head/on the pistons. it took a while to figure out. just a thought!
 
boostdprotegelx said:
there was an issue similar to this years ago. the butterfly valves inside the intake manifold had come apart and were banging around inside of the head/on the pistons. it took a while to figure out. just a thought!
Click to expand...

Whoa.. That sounds like it would make some pretty bad noise though...
 
pcb said:
That fuel treatment should have cleaned things up.

The way you describe the bouncing idle sounds exactly like my car when it's relearning to idle.
700 rpms, then the ECU hands over control to the IAC and it fails it's attempt to idle, so the ECU takes back control, brings the RPM back to 700 then tries to hand back control to the IAC again... learning from the other attempts.
My idle wouldn't drop as far with each attempt, until the idle stabilized at 700 RPM.

Your car may simply need some time to figure things out with a bunch of idle attempts at different engine temperatures and other conditions.
Click to expand...

Maybe, but i mean it doesn't seem to get better, even after driving for a week to and from work (20+ minutes each way with stop and go). It's like a hard drop and then recovery, not a oscillation.
 
Yea,.. That should have been enough practice for the IAC.

The only other thing I can think of is, one guy who used an aftermarket IAC and it simply would idle properly.

He installed an OEM IAC, and that fixed his problem.

He said he took both apart and the hole or vent was smaller in the aftermarket version and it just wasn't getting enough air through.
 
pcb said:
Yea,.. That should have been enough practice for the IAC.

The only other thing I can think of is, one guy who used an aftermarket IAC and it simply would idle properly.

He installed an OEM IAC, and that fixed his problem.

He said he took both apart and the hole or vent was smaller in the aftermarket version and it just wasn't getting enough air through.
Click to expand...

I saved the original IACV. I will clean it up and try swapping it back out with the aftermarket one and see if it works, assuming the shop can't find anything. I bought the nicest one on rock Auto for $180! The OEM one is like $400!. That's the only reason I had to try aftermarket.
 
devinw said:
... rock Auto for $180! The OEM one is like $400!. That's the only reason I had to try aftermarket.
Click to expand...

Yea no kidding... Sometimes OEM is 3-4 times as much money.

The only thing I might go OEM with is coils.
Those damn things can be bad brand new out of the box.

(although mine are Beck-Arnley and have been working fine for years)

There have been a lot of people here on the forum dealing with a crappy idle...
Some guys have have just given up and got rid of their car after years of frustration.
 
pcb said:
There have been a lot of people here on the forum dealing with a crappy idle...
Some guys have have just given up and got rid of their car after years of frustration.
Click to expand...

That just seems insane to me. I've owned a lot of different brand cars (American, Japanese, German), and never heard of a simple issue being simply unresolvable, to the point of just ditching the car. There has to be a solution. Mazda can't be that bad.
 
Well... My car runs great, with smooth idle.
I assume most P5's do and it's just the few that don't run proper that come to the forum for help.
An actual Mazda mechanic may be better able to deal with the problem with their specific knowledge of our car ??

I'm thinkin, if it happened to me and I was stumped, I'd play with my throttle position sensor... Crank it up to 1% so the ECU never sees 0% and tries to idle it...

I kinda think that might work without pissing off my ECU and throwing all kinds of codes at me ???
 
I had a similar issue but it would be when i push the clutch pedal in and the rpm would drop very low before stabilizing above 500. It was because I had a vacuum leak, one of my hoses were split. imo most common cause of idle issues are caused by vacuum,air leaks.
 
Speaking of vacuum leaks,...
Did you spray around your engine with carb cleaner to check for leaks ??
 
I didn't do the carb cleaner test, but I did really give all the hoses a good inspection. I guess I will try that later if the shop can't figure it out.

Just dropped it off this morning at a really good shop we know. Will report back if they find anything. Fingers crossed.
 
Update: took it to the shop last week and they did a "smoke test" on it and somehow found a vacuum hose back there in the EGR system that was leaking! I thought I had inspected all the hoses, but damn, it seems you really need a better way than just a visual to find these problems.

After all that, the hose was replaced, and the idle dip is completely gone. Kind of pissed I wasted so much money on IACV, EGR valve, etc... but whatever at least it is done!
 
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