Weird Idle need help
 

My idle has been kinda weird. On a cold start, it would start up and run normal but after a pretty lengthy drive if I shut off the car and started it up again the idle would at weird, almost to the point of stalling. Actually there were a few times that it did stall. At first I thought it was a vac leak but figured it would be more consistent if it was but changed all my hoses anyway because they were old. Idle got better but still seems to do the same thing after a drive. What else should I check?

<iframe width="560" height="315" src="//www.youtube.com/embed/EtU5SueUi3A" frameborder="0" allowfullscreen></iframe>

was that you hitting the gas or was it doing that on its own.

As far as that sluggish idle, my car will do that too if I fire it up after getting it nice and warm, although it only does it for a few second than evens out again. Mine will also stall if I don't catch it, but like I said it immediately returns to normal after a few seconds.

I have had the issue with an old tired engine, the now brand new engine, and yes I have replaced the injectors.

It was both in the video but usually I wouldn't have to hit the gas to do it.

I have the same issue. Its fine after I tap the gas. But it would be nice to know what the cause is. I have an 88 vert 167k original miles.

I am actively searching about it as we speak.

It isn't leaky injectors, I have ruled that out myself. It's almost like the ECU is dropping too much fuel at start up and then the engine needs to clear it out before the idle corrects itself. The hotter the engine, the worse it is I have noticed. I do not have this issue in the winter time, but in the warmer parts of the year, it seems to come about after the engine has a good heat soak (good drive, shut her down and come back 20 minutes later).

On Feb 22nd I did a SCCA road rally and was really hard on the car. We got to the finish and was in there for about 30 minutes and the engine fired up and immediately flooded after it started. I cranked it over a few times doing the S5 deflood and then cranked it without and it sputtered until it got all of the excess fuel out. Like I said, I had just beat the snot out of the car for a couple of hours. Normal driving, when i shut her down and it heat soaks, I can just blip the gas and get it to act right.

As I stated earlier just in case the next posters didn't read. I had this issue with my old and worn out 160k mile original mazda factory engine, and I still have this issue with the NEW** engine.

** Rebuilt engine using brand new irons and rotor housings. The only thing reused was the rotors themselves.

Hopefully someone might have an idea so we can all fix our problems!

I have spent countless days wasted on figuring out stupid issues like this. You will never find one solid answer, even if the 2 of you are having identical issues. And you know what I found out? It magically goes away when you replace the entire engine harness and ecu. The fact is that this car is over 20 years old with engine harness connections that aren't weatherproof.

Not to sound grumpy or mean, it's the truth. And the sooner the fate is accepted (that you'll be purchasing a standalone and harness soon) the less time and money you will waste, and the more you will love your car.

I understand what you mean AGreen but even various answers would be alright with me so I could possibly checklist it. The only thing I could remember was that it started happening after one day I drove until I completely ran out of gas ironically to get gas..that was only a stop light away..so close...So my next guess would've been clogged fuel filter and injectors maybe?

And there's a fuel sock in the fuel tank.

What else should I check that might cause this?

Fuel system pressure and flow would be a good place. TPS too to cover all bases and TPSs cause everything so check it anyway!

I have already knocked out what has been mentioned in this thread. Fuel sock replaced as well as the TPS.

+1 for AGreen. I myself have sort of gone through and tried to figure out this strange issue; I've also yield it to have multiple causes and aren't really easily fixable. My guess would be the wires and wiring are getting delayed or off signals since the wiring itself is starting to build up resistance on its own. You try checking the TPS? I've never installed a TPS without measuring its OHMs. Many I find (especially for used cars) are kind of junk or set wrong to begin with.

The best way to diagnose a car like this is to get a multimeter and a paper clip. Use the paper clip to back probe the connector at the ECU and check all the voltages at the pins to ground. The FSM has a chart in the Fuel/Emissions section that shows a rear view of the connector, and it labels all the pins alpha-numerically. Check all the voltages, then compare them to the chart. The chart will also specify the conditions too, such as "engine warm", or "key on".

Also, check for vacuum leaks using brake cleaner, and check proper fuel pressure and spark. Once you've verified everything's good, see my original post and you'll see why I say what I do. I've ran in to these issues several times with mine, and each time it was found that NOTHING was out of place. It would randomly idle poorly, I'd get hesitations at random RPM, etc. I checked Every. Single. Component. I even had it hit a brick wall a few times, so I drove it with the voltmeter hooked up to the ECU. Once each pin was verified to have all the right voltages right where they were supposed to be, and after I verified fuel pressure by hooking up a gauge (taped to the windshield so I could watch it while I drove), I gave up on it. I swapped ECUs, re-grounded all the grounds, continuity checked all the wires, replaced all spark plugs, wires, and checked literally everything. I built and installed a Megasquirt and have not had an issue with that, even on my own shitty tune.

I'll try to check out what you guys suggested when I have some time. I don't have random rpm hesitations though. It only did that when I was at a stop idling or when I turned the car off and on after driving somewhere but even then it was random if it did that or not. I just redid all the vac lines...that I could find anyway..and that seemed to help(car won't stall out anymore at least so far). I don't think I'd go as far as to get a Megasquirt or anything though since my cars just a little N/A all stock...just trying to keep the thing running haha. Thanks for your inputs.

you losing any coolant on this car at all?

Yeah but I already know it's from the water pump housing which is my next to do. I guess if I'm still losing coolant when I get that fixed then I got more things to worry about than idle lol.

Try taking the BAC valve off and cleaning it with some throttle body cleaner and a toothbrush. Use a 12v source (there are only 2 pins on the BAC) and verify it moves open when you apply 12v to the solenoid.

The BAC is the "Bypass Air Control" valve. The ECU pulses a signal to it. It uses a pulse-width modulation circuit to vary how long it's open each pulse. So it always operates at the same frequency, but each pulse length is different (longer or shorter). So if that's sticky, it may not be acting fast enough to account for changes in RPM.

extremely worn spark plugs will exhibit those symptoms, so will low fuel pressure, vacuum leaks or a sticky AFM vane.

the BAC could be possibly at fault, but only if the idle is lower than specification sais for the idle screw to be set at. a properly set idle speed should never allow the car to idle low enough to stall out even when heat soaked.

The spark plugs are new, just recently replaced. That was the first thing I did and then replaced the vac lines. I'll probably check out the BAC and AFM first, thanks guys.