Idle surging..

[_lithium_]

Ok, my 1992 Mazda MX-3 was at a red light today, and it started to fluctuate between 2k-3k RPM, I turned the engine off, and now it won't even turn on but just sounds like it wants to start but can't fully get there. (It's not just standard turn-over sound but sounds like it is almost going to start but can't fully). Any ideas?

[Nd4SpdSe]

sounds like it wants to start but can't fully get there. (It's not just standard turn-over sound but sounds like it is almost going to start but can't fully). Any ideas?

Symptomes sound like your typical failed ignition module (search "HEI Mod", also see viewtopic.php?f=23&t=53706), except for the high-idle before the car died.

[_lithium_]

Well, I just got back from going up to my car and it actually started right up....


Went to check the engine and found the metal cap next to the radiator wasn't down all the way and was spilling coolant. I don't know if it's gonna still do the fluctuating though, would a lose coolant cap be the cause of this s---?

[Daninski]

You have a coolant temp sensor that adjusts idle if the coolant is cold to a high idle then controls idle to fall to 700rpm once operating temp is reached. If there's no coolant for it to get an input from then yes you could have wandering or high idle. Search IAC
When filling your coolant system always ensure you purge the system of any air. The IAC is at the top of the system so any air ends up there and screws up the IAC reading. I Squeeze the top hose with the filler cap on and that seems to get any air out of the system

[_lithium_]

Well I think the coolant issue was solved but now the car starts up just fine, but the rev is jumping while idle (doesn't do it when in gear). Is the TPS responsible for this most likely? What would be a way to figure out what is causing it?

[MrMazda92]

First I'd try and unplug the IAC, as it is about the easiest first step you could pick. That solved my problems, at least temporarily. I'll find out why it caused them later on. If this solves your problem, you've got a sensor somewhere that's getting readings it doesn't like. May have failed even.

After that, I'd clean the throttle body, adjust TPS, and adjust the Butterfly valve stop screw. This last one was off on my car, and did affect my idle. wytbishop pointed it out as a remote possibility, and sure enough it was part of my solution.

Your last step, after stabilizing the idle, is to re-adjust it to factory RPM range. When you jump Ten/Grnd, set it between 550-700 RPMs for near factory idle. Then unjumper it, and it should go up between 50-150 RPMs. That will be your new idle, unless something changes.

[_lithium_]

Well I don't even know where the IAC is or how to do most of the fore mentioned stuff lol. Isn't surging only causewd by TPS failure? I was thinkin of just putting a new one in

[Newfie_dan]

No the coolant temp sensor plays a big role in surging, an air pocket around the sensor area makes the car think its colder than it really is so it drives the idle up, it must be totally submerged and mazda in all their genius stuck it right where it will be dry is the slightest air bubble is in the cooling system. There are 2 coolant sensors, 1 for the dash which has 1 wire and the 2nd for the ecm which has 2 wires, both are located in coolant neck passenger side close to the filler cap, check the coolant level first off. I have this surging issue whenever it gets cold here, oddly enough so I am considering the hei mod to see if it fixes that issue.

[MrMazda92]

You can unplug the IAC right beneath your Throttle Body, it should be a white(yellow with age?) plastic plug with a quick release. Mine was hard to remove, the plastic tab wouldn't budge at first. That will bypass the sensor listed by Newfie_dan above me(and others), although that isn't necessarily a good thing. In my case, it was more benefit than risk.

That is the exact reason you need to be sure that your engine warms up adequately after startup, it won't know to do that on it's own. I give mine about 7-10 minutes before I drive it currently, it's also about the amount of time it takes for my shifter to move smoothly. That's as good a tell as any I imagine, as rough shifting can't do the car any favors either.

Newfie_dan put it in better words than I have, and he's exactly right. My list above your post has other info, but you'll need to search for how to accomplish some of it. Some of it should be stickied, it was last I checked.

Good luck!

[_lithium_]

So, I actually unplugged the TPS (while car was on and surging) and there was no difference and the car kept surging. I unplugged the IAC and the car low-idled for a second or two, then died. I took the entire Throttle body out the other day and spent a few hours using Throttle Body Cleaner and cleaned the hell outta it (had a s--- ton of black hard stuff (oil? grease?) but none was within the IAC body. I put everything back together and it still surged.

After driving it around for a bit afterwords, I was kinda noticing that if I try to hold it at any RPM (I tried like 2500RPM) the car would hold for a second, then feel like I took my foot off the gas but felt more like it shuttered forward then the RPM's began to fall. I'm gonna go drive it again and just see if maybe it was a mistake on my part with my foot position but it felt really weird.

[Ryan]

Why has no one mentioned intake leak yet...

[_lithium_]

UPDATE::

Got it fixed, It turned out to be severely low on coolant (but temp on gauge never went past half way so it was enough i guess) so im guessing it may of caused the idle surging while sitting still. Put a new Throttle Position Sensor in and works like new now. After a while, the car stopped surging on it's own and i unplugged the old TPS and it acted like normal.


Thanks for all the advice/tips guys!

[MrMazda92]

Ryan,

Good point, my bad on that one... that contributed to my own idle issue!

Glad the problem's fixed, at least you know how to deal with any further issues regarding it!