97 Galant Low Idle/Stall Problem

New to the forums but it seems like a fantastic resource. Nice to see people using the web for something helpful and productive!

Here's the story:

Driving home from work Monday and the car overheated. First time issue with no warning at all. Limped it home stopping occasionally to add water (fun in the Texas Summer heat - :icon_rolleyes:).

I believe the culprit was the thermostat but it busted a seam on the radiator when it went. So new thermostat, gasket, radiator.. flushed, bled & filled and the temp is now good to go.

Unfortunately the idle isn't. When I first fired it back up after all the above it was idling low @200-300. Couldn't run the AC at all without it dropping to 100 or stalling. Disconnected the battery and did the idle rev up and drop down thing to reteach the ECM and drove it around a good bit. Seemed to help and idle steadied out, even with AC on, but was still a little low (@400-500 but dipping a little at stops).

Got up this morning to drive to work and back to square one with the idle. @200 or so with no AC, won't run with the AC on.

Now I can two foot it (one on the brake & one on gas) and get it to idle steady with or without AC.

I guess my question is would overheating damage the IAC? Temp Sensor?

I'd rather not have to replace the IAC or even mess with the throttle body for that matter, so simple solutions & suggestions are obviously preferred. This car isn't my pride and joy like with most of you guys, it's a daily driver I bought just for a long commute to save gas vice driving my truck.

Also read where someone was having idle problems and adjusted the throttle cable to offset it... good or bad idea?

Sure would appreciate any help you guys can offer.

Thanks.

- Gunny

could be a temp sensor, just asking if the mass airflow sensor is plugged in as it would cause it to barely run. no check engine lights? the FIAV or IAC could be acting up but once the car warms up the idle should be on, if you hold the gas to make it idle at 800 or so for a minute then let off does it go back down or stay up?

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Originally Posted by Galanttuner10

could be a temp sensor, just asking if the mass airflow sensor is plugged in as it would cause it to barely run. no check engine lights? the FIAV or IAC could be acting up but once the car warms up the idle should be on, if you hold the gas to make it idle at 800 or so for a minute then let off does it go back down or stay up?

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MAF is plugged in. No CEL is on. I can keep the idle up with the pedal, but as soon as you let it off it will drop back down.

If I try to adjust it up with the BISS will the IAC/ECM attempt to auto correct the idle? And if so can I unplug the IAC and then manually adjus the idle?

Cold starts are fine, it auto idles up to about 1200-1500 for a few seconds and will drop down to about 600-700 in Park. Once I start moving though it will nearly or sometimes stall completely at a stop. Turning the AC on will cause it to stall.

Occasionally it seems to try and correct the idle if it doesn't stall, but will only bring it up to @200 or so. Just barely enough to keep it going.

Unplug the IAC and adjust idle with BISS then reset the ECU by disconnecting the battery. Plug everything back again and see what happens. The idle with the engine warmed up should be around 850-900, but 1000 is also ok. Just dont go over 1200 cuz it will start oscillating .

Something in the FIAV might have got thrown off balance when it overheated. The FIAV is fed with coolant to act as a choke in the morning.

Ok, quick update. Went to see if Oreilly's could pull any pending codes, even though there no CEL, but of course their scanners are crap and can't get anything but active codes.

On the way out of the parking lot a miracle happened and the CEL lit up! Pulled back in and coded out to:

IAC (of course), and/or O2 sensor (upstream).

I guess my questions now are:

1. Should I try the cheaper fix and replace O2 sensor first? Problem seems intermittent. On the way home the car idled fine.. if that's any kind of clue.

2. Can I simply disconnect the IAC harness and adjust the idle at the BISS or does that require a block plate? And a follow up, since I live in DFW area and we have emissions testing, .. will a black plate mess with that test by throwing weird codes on the OBD?


Thanks for any and all help!

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Originally Posted by mko

Unplug the IAC and adjust idle with BISS then reset the ECU by disconnecting the battery.

Something in the FIAV might have got thrown off balance when it overheated. The FIAV is fed with coolant to act as a choke in the morning.

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Didn't see this when I posted. So unplug the IAC and adjust the idle.. plug the IAC back in before resetting ECU, or leave it unplugged?

Can it simply be left unplugged if I adjust the idle up to say 800/900 so it's still fairly smooth under AC load?

It can be left unplugged as long as weather is warm, but when it get cold that baby won't wanna start and hold idle, you also might die if making a hard turn cause the power steering pulley will suck some power from engine, ac will also make the car stall time to time if you don't adjust the idle for it.

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Originally Posted by bgood12

It can be left unplugged as long as weather is warm, but when it get cold that baby won't wanna start and hold idle, you also might die if making a hard turn cause the power steering pulley will suck some power from engine, ac will also make the car stall time to time if you don't adjust the idle for it.

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Good to know. Luckily I live in Texas where it's warm most of the time. Will try that tomorrow, this weekend at the latest and report back.

What do you guys think? Shoot for @900/1000 in Park? Will that give it enough wiggle room to offset the AC running and any pull from braking & turning?

1000 should be good I think, I had this happen for a year before I found the bad wires on my iac so just keep the screwdriver in the car at all times just in case.

Many times when you mess with the biss screw you mess up the idle. I recently went through where my car would idle surge. I fixed it by turning on the headlights and heat and setting the idle to 850-900 rpms and haven't had an issue since. Put the screw in all the way then back it out about 2.5 turns and disconnect the battery for 10 minutes to delete the codes and reset the ecu, with a bad IAC the car should only not idle itself on cold starts but once the engine is warm the idle should be fine as I killed my IAC before as well.

Thanks a ton for all the input. This thing is my DD I use to keep my 35 mile each way commute from racking up miles on my Ram, not to mention in the last year it's paid for itself in gas savings over driving the truck.

Other than the idle, it runs like a champ.

With what you've posted I'm confident I can get it smoothed out this weekend and if it becomes an issue when the weather cools off I'll slap a new IAC in it.

Thanks again!

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Originally Posted by Galanttuner10

Many times when you mess with the biss screw you mess up the idle. I recently went through where my car would idle surge. I fixed it by turning on the headlights and heat and setting the idle to 850-900 rpms and haven't had an issue since. Put the screw in all the way then back it out about 2.5 turns and disconnect the battery for 10 minutes to delete the codes and reset the ecu, with a bad IAC the car should only not idle itself on cold starts but once the engine is warm the idle should be fine as I killed my IAC before as well.

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That's exactly what I did and the idle isn't dip into the "engine gonna stall zone" anymore. It still dips from about 700 to 400 or so when the compressor kicks in, but I can live with that for the time being.

Probably wouldn't be as noticeable if the motor mounts weren't needing replacing. :079:

Thanks again for the help..

i also dont have AC but you should be able to raise the idle with the biss to around 1000 and hopefully it wont go as low

Just to update this one. Car wouldn't pass inspection with IAC disconnected. Got another IAC from Pick N Pull for $26.99. Thanks to some advice in another thread was able to install in about 1/2 hour or so. No more CEL, idle back to smooth!

Thanks all.

Alrighty, apparently there's no rest for the wicked. Check Engine Light is out, and the car has been driven roughly 50 miles or so it could relearn the idle. Everything seems fine except the idle is a little low. In Drive it's sitting right at about 500 RPM. Parked it climbs to about 650. First started it goes to about 1200 or so then drops down after it warms up a bit. The IAC is definitely working because it adjusts for the A/C kicking in and holds steady, but low.

Do I need to play with the BISS?

Also, just out of curiosity, how does the TPS interact with the IAC?

Do you know that the code is still for that and not something else? Turn the heat on and headlights and play with the biss screw until you get the idle around 850-950

There's no CEL now, just the idle seems a little low. It's rock steady @600 RPM now, but I thought it was supposed to be 750-800 or so.

Like I said, turn on the head lights and heat and back out the BISS screw until you get the idle where you want it.

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Originally Posted by Galanttuner10

Like I said, turn on the head lights and heat and back out the BISS screw until you get the idle where you want it.

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Ok, I tried this today after work. Car was warmed up from drive home. Lights on, heat on full. In park I was able to adjust the idle up to right at 800-850. Really steady there.

As soon as you shift it to drive it drops down to 500 or so. With the AC on it actually idles up a bit to like 650. Headlights and heat on it will sit at 500. With just lights on sitting in Drive it will eventually drop to about 450. It doesn't stall or jump around, but it seems low.

It almost seems like an electrical issue, but the Alt light isn't coming on. It has a new alternator and battery from a few months back.

Any reason why adjusting the idle in Park wouldn't result in any change in the idle in Drive?

You can clean the IAC and see if that works i know im posting months after the fact maybe it will help others...
I read that they sometimes get carbon depoites or whatever and cause low idle or rough idle because it cant open and close properly..