Having some odd troubles, can anyone advise?

[MrMazda92]

So, let's say that the IAC in my mx3 is the issue here. Can't say I'm 100% familiar with the part as I've not had to mess with it before. Is it possible to repair one or would it require replacement? Been looking at prices online, not finding one very cheap.

Is there a website anyone knows of that gives more detailed information about this part/system in general so I can get a better understanding of it's function? My engineering mind wants to know more

Short of unplugging it, is there anything else that can be done? What sort of effect will disconnecting it have over all?

Looks like I should finally get around to fixing the exhaust on my RX7 and drive it for a while instead

Unplugging it is a temp. fix for the idle issues I was faced with, I wouldn't suggest it unless you're having problems with it in the first place. I actually believe mine is stuck open, so I'll be following Inodoro's advice next time I tear into the car for a weekend job. Some people do a complete delete of the IAC, they will put a blocker plate over the valve's stock location, and I'm not sure what they do about the wiring harness. I actually miss not having to jam the clutch in hard to compensate for too little throttle when backing up... I'm getting annoyed with my driveway.

[ZeroLux]

Ok.

Still have not had the chance to take a look under the hood on the MX3 yet but I am starting to wonder.

Let me toss out a few more facts here and see if it can be narrowed down some more:

1. the car has NO issue whatsoever in reverse from a dead stop. this problem ONLY appears when starting in 1st (no i have not tried 2nd yet)
2. it OCCASIONALLY (when either the car or my foot is getting pissy) manifests itself in LOW second (right after a change up) but does not last long
3. the car has zero idle issues that i know of. always steady, short of right after i bought it but the car needed some adjustment.

This only happens when I am applying gas and letting up off the clutch in first to get rolling. The result can go different ways depending on how I allow for it, one of the most notable short of it trying to choke out is that I get moving in first, fully off the clutch, and I get jerked around (for lack of better wording) it lurches a good six or seven times until I get fed up with it and either switch to 2nd or play with the clutch/gas again in 1st.

Would this still sound like the IAC to you guys? I'm having my doubts a little but I will admit I've done very little to this car repair-wise since I bought it and I am more than open to suggestion. Anything else I could take a look at when I'm under the hood next?

[Inodoro Pereyra]

Would this still sound like the IAC to you guys?

I think so. There aren't so many things that can cause that problem in an engine.
Either way, troubleshooting an engine without seeing it is always difficult, so be patient. If it's not the IAC, we'll just keep at it, until we figure it out.

[cWs306]

we'll just keep at it, until we figure it out.

Your just so positive! ahaha.

[MrMazda92]

Lux... I have a question, what RPM do you shift from 1st to 2nd at? I tend to shift up at about 1,500. That's how I avoid what you describe as lurching, because 1st is just so torquey.

[ZeroLux]

You mean where do I shift under normal driving? That all depends. If the engine is cold I typically shift low, not sure where exactly but under 3k. Only difference is early mornings there's a large hill after a right turn at on a main road I have to take to get to the highway, and to avoid being hit by people at-speed I tend to let 1st run up higher.

All the lurching I am feeling is before I can even leave my road and all at low rpm and speed.

I would not say I beat on the car too much, but I do tend to lead foot it most of the time once it's warmed up, however I typically don't push her past 5k on the tach in any gear unless I have a reason to. Typical shifts I change up around 4k most of the time under normal driving. As my father once said after I started driving so long ago "you like to be doing the speed limit before you are past the green light"

Car has been great up until now. Bought it two years ago with 101k original miles on the clock. All original down to the stock radio and cd player from Mazda. Paint is a little worse off now than when I bought it, the clear coat on the hood and rear spoiler is hazing from sunburn. I'd love to fix that sometime but costs a bit more than I can do right now. Did all the initial maintenance I could with a new water pump and timing assembly shortly after I got it. Put two new axles in it due to torn boots on the outer side. Refilled the trans with Mobil-1 75w90. Denso plugs, NGK wires. Really fighting the urge to go ZE with it.

One thing I don't know, since this was mentioned earlier... I have no idea the actual physical condition of the existing clutch, nor do I know if or when it was ever replaced. Logically one would guess it probably has, but seeing how pristine the car was when I got it, I don't think the original owner drove it much, so I suppose it's possible. I do know that it appears if anything was replaced under the hood over the years that it was done with OEM parts.

[cWs306]

"you like to be doing the speed limit before you are past the green light"

That.. made my day! ahahaha.

Btw.. your car is mint! holy eff. and Dont fight the urge! ZE THAT BEAUTY! you will not regret it AT ALL.

[ZeroLux]

Thanks! I knew it was a great buy the moment I saw it, surprisingly it didn't take any convincing on the wife's part either. I'm trying to keep her in as good of a condition as I can but being my DD most of the time that gets difficult.

Well, just gave disconnecting the IAC a shot. I assume I pulled the right plug, appeared to be a 2-wire white plug attached to a black cylinder directly under the TB. Got the same results as before, hesitation, lurching, etc.

I did notice that when I disconnected it prior to starting the car that it caused the car to NOT rev up on a cold crank as usual. It just started, stumbled quickly, and flattened out at idle. Smelled plenty of gas due to the cold start and running richer without additional air flow.

Any other thoughts? Or did I do something wrong here I could try again?

Anyone have a spare ZE sitting around they want to part with for cheapies?

[MrMazda92]

Mint looking If you can't fix it, I'll take it!

That's to be expected from the IAC, and you did disconnect the correct plug. The IAC does cause it to idle high on cold start, so I'm positive you unplugged the right one. That's how I have had my car for nearly a year, and honestly It's not a huge hassle for me.

The reason I mentioned your chosen RPM for shifting from 1st to 2nd only(it's where the problem is worst I imagine, It certainly should be!), is that the gearing in our trans. is very short... I literally do the 1st - 2nd shift at about 1,750 RPMs, and then anywhere from 2,000-6,500 for the rest. If you try to accelerate and then decelerate in 1st, the car's going to lurch like you're a MTX noob dumping the clutch. That's why if I'm going above ~3 MPH, I keep it in 2nd. First gear is almost useless for me...

[Inodoro Pereyra]

+1 on the comments about the car. That thing is gorgeous.
However, I think you should disregard MM92's comment. You live in NC. If you feel the need to give the car away, I'm closer. You're welcome.

Anyway, seriously now, I'm gonna make a comment that's probably gonna earn me some flaming. I would NOT ZE that car. Yeah, I know the ZE has more power, but, seeing the shape that engine bay is in, swapping the engine would be a mistake, IMO. There's something insanely cool about an engine bay in such a mint shape.

Now, going back to your problem, MM92's comment raises some good questions:

1. Is your engine lurching only in 1st gear, or do you notice it in all gears?

2. At about what rpm range is it happening?

3. Do you hear the engine missing?

Initially, pending more information, I'd say, check you spark plugs (yeah, I know they're new. Check them anyway, see if they're in good shape), replace your fuel filter, and check your vacuum. Being that you have run seafoam in the fuel consistently, I'd concentrate on the fuel filter, as it may have gotten clogged with gunk your seafoam got dislodged from the gas tank and/or lines.

[SuperK]

SuperK is closest!
I'll be up this weekend, pick me up from the airport, I'm driving it home!

Heck, I'll even pay you for the car!

[Inodoro Pereyra]

SuperK is closest!
I'll be up this weekend, pick me up from the airport, I'm driving it home!

Heck, I'll even pay you for the car!

Hey Zerolux, I wouldn't advise you to take that offer. He has a tendency to drop trees onto his cars...

[ZeroLux]

Hah! You guys are crazy.

Sorry, but I usually own cars until the wheels fall off. Don't see the MX as being an exception any time soon.

So to answer those questions:

1. Lurches primarily in 1st, SOMETIMES I feel it in a low 2nd gear.

2. I watched it last night, I was fluctuating between 2500 and 3000 on the tach in 1st trying to keep power but it kept wanting to drop around 900-1100 rpm's pretty quick for no reason.

3. Engine isn't missing. (I looked last night, nobody stole it ) Runs smooth at idle, runs smooth in all gears past the issue, gets up to speed fine.

I'll check out the spark plugs and probably do a compression test at the same time (just for sanity's sake), have not done the fuel filter- but wouldn't FF problems manifest at higher rpm's and not lower? The RX7 I have here had a bad FF about a year ago, plugged with rust, it would do fine until I wanted to cross 4k then it would cut out from fuel starvation. I also saw a few things online last night on the Probe forums about the air intake pipe might have a tear in it or a vac leak somewhere. I've checked all I can, did not see any leak but I could have missed one I'm sure.

If needed I can get out there sometime and take a video of how she's acting and post that up.

[Inodoro Pereyra]

Ok, that's good to know.
I would replace the FF anyway, if nothing else, just to be sure it isn't an issue.
Besides that, Take a real good look at your accordion tube (take it off the car, wash it (although dirt doesn't seem to be much of a problem in that engine), and look for holes or cracks, especially in the seams). Also make sure all the hoses connected to it are in good shape.

[SuperK]

Superk has his two cent troubleshooting list!

Distributor... Sneaky suspicion its this
VAF- mine went bad... Wasnt a way to test it. Horrible stutter
Fuel filter/strainer
Thurnongulator
O2 sensor. Unplug them and see if its different