Car is idling VERY low

[byebye_sti]

Saturday night the starter in my car went and before that it would run fine and idle at about 750 to 1000.

Yesterday I replaced the starter and when I started it up it seemed to be idling fine.

This morning, before school, I started it up and it was idling fine again. I figured there would be no problems.

On my way to school I had to stop quickly and threw the clutch in, the RPM's immediately dropped and the car died. This was unusual, so I kept an eye on all of my gauges. When I got to the stop sign right before the highway I threw in the clutch again and it died.

The car was idling at about 625-650 most of the time and sometimes even lower. It would only die when I threw in the clutch though. My oil pressure gauge was also reading a bit lower than normal.

Could this have anything to do with changing the starter? I do have a slight oil leak that I am getting fixed today. Could that be the problem? I'm not sure what to do, because I don't like driving it like this with the chance of something getting messed up.

Would not tightening the starter really tight have anything to do with this?

Any help is greatly appreciated. Thanks!

 

[Boost92awd]

Did you disconnect the battery when you changed the starter? Have you tried turning the BISS screw to make the idle higher?

 

[byebye_sti]

Did you disconnect the battery when you changed the starter? Have you tried turning the BISS screw to make the idle higher?

Yeah I disconnected the battery.

What is a BISS screw?

 

[Boost92awd]

What is a BISS? Base idle set screw. This is used to set the basic idle point for your car, around which the ECU will attempt to control the engine speed. Failure to have the BISS set properly can lead to all kinds of weird idle problems




My car does not idle very well. Is there a fix?

If this process doesn't work, you are in the minority. Try looking for something basic, such as a loose throttle cable, first. Other sources of idle problems include fouled spark plugs, a defective or gunked-up idle speed control (ISC) motor, leaking injectors, a cracked vacuum hose, or a damaged intake manifold gasket. High idle can also be caused by a throttle cable or cruise control cables that are too tight.

Some troubleshooting tips: if your idle adjusts when your A/C compressor is on, or when all of the electrical accessories are on, the ISC is at least partially working. If your idle appears to fluctuate with temperature, suspect an air leak in a vacuum hose or at the air intake first.

If you need to check the ISC, do it when it is hot. The ISC resistance can sometimes change when it has cooled down. Thus, the ISC looks ok when checked, but misbehaves when actually operating. The same holds true for cables since they can tighten up during operation.

 

[gregalmighty]

Its on your intake manifold, a little left of center. Look at this pic: http://members.shaw.ca/dsm.1000q/Engineprimer/2G/throttlebody.htm

Here is a link to the index of that site : http://members.shaw.ca/dsm.1000q/Engineprimer/2G/throttlebody.htm

Its useful if you aren't real familiar with everything thats under the hood.

Is your blow off valve recirculated?

I would check for a boost leak, that can cause the problem you're having. So can the bov being vented to the atmosphere. Almost every dsm will run how you are describing, I highly doubt this, but was the ac on?

Check for simple things first like a boost leak, fouled plugs etc. then take it from there.

 

[Noogabox]

Sounds like your idle is running rich. Raise your idle ( let a lil air in) You can do it with the BISS Screw. However if you didnt change the setting and all of a sudden it is idleing lower you have an overly rich situation. You may have a more important issue with a sensor. however you can temp fix it with the BISS

 

[costas14]

DONT TOUCH IDLE SCREW AT ALL, THIS HAS HAPPENED TO ME TWICE ON MY 1.8

everytime you disconnect teh battery your ecu clears or whatever, so when you go to drive it, rpms will drop and car will die, happened when i chagned starter and my alternator and my battery, drive it around in a parking lot or near your house for 5-10 miles, your car will die but dont use the starter to start teh car, put it in 2nd gear or 3rd, and let off the clutch should turn back on, took about 10 miles when i changed my alternator to get my idle back to normal, same thing with the starter, and battery change, also this has happened on my 90 gst when we had to recharge the battery

 

[byebye_sti]

DONT TOUCH IDLE SCREW AT ALL, THIS HAS HAPPENED TO ME TWICE ON MY 1.8

everytime you disconnect teh battery your ecu clears or whatever, so when you go to drive it, rpms will drop and car will die, happened when i chagned starter and my alternator and my battery, drive it around in a parking lot or near your house for 5-10 miles, your car will die but dont use the starter to start teh car, put it in 2nd gear or 3rd, and let off the clutch should turn back on, took about 10 miles when i changed my alternator to get my idle back to normal, same thing with the starter, and battery change, also this has happened on my 90 gst when we had to recharge the battery

I have been doing this when I'm driving and it dies. I drove it for about 10 minutes this morning to school, then another 10 back home. The only time it was idling perfectly was when I came home and parked it. It went back up to 750-800 when I parked it. When I was driving though and say I stopped at a red light or something it would be down at like 525-565. It died twice on the way home.

I'm not sure what to do.

 

[Boost92awd]

Turn the BISS screw. Remember once you turn it you have to turn off the car and turn it back on to get it to change the idle.

 

[byebye_sti]

Turn the BISS screw. Remember once you turn it you have to turn off the car and turn it back on to get it to change the idle.

But the guy above said don't touch the screw at all?...

 

[Boost92awd]

But the guy above said don't touch the screw at all?...

Well you already did what he told you to do and you still have the problem. Thats all the BISS is going to do is change what your car idles at. I'v had the same problem where my car idled to low and what I did to fix it was turn the BISS screw. Remember you can always turn the idle back down.

 

[byebye_sti]

Well you already did what he told you to do and you still have the problem. Thats all the BISS is going to do is change what your car idles at.

Okay, then that's what I shall do.

I read up on some of that stuff about messing around with the BISS screw and it sounds like there is a lot I have to do. I can't just go out there and turn it right? I have to like ground some things and what not? WTF

 

[Boost92awd]

Turn you car off, turn the screw alittle bit, turn the car back on and see where it idles. If not high enough or to low repeat those steps. Its very easy, its just you have to turn the car on and off, this is just a different way of doing it.

 

[byebye_sti]

Turn you car off, turn the screw alittle bit, turn the car back on and see where it idles. If not high enough or to low repeat those steps. Its very easy, its just you have to turn the car on and off, this is just a different way of doing it.

Oh okay, easy enough. Thanks!

I'll go try it now and then I'll let you know how it goes.

Oh, BTW, which directions turns the idle up? To the right?

 

[kenamond]

What doesn't make sense is that the ISC is supposed to adjust the idle to 750rpm regardless of the BISS (to some extent). It's not doing this. This either means the ISC is not doing its job, or it's at the end of its range and can't open it up any more to increase idle. The BISS just gets the idle airflow in the ballpark for the ISC. What am I missing?

 

[Boost92awd]

Oh okay, easy enough. Thanks!

I'll go try it now and then I'll let you know how it goes.

Oh, BTW, which directions turns the idle up? To the right?

Remember to get the car at operating temperture before you start messing with the idle, I want to say turning it right will turn up the idle. But not 100% sure on that as I havent changed my idle in a long time.

 

[Boost92awd]

What doesn't make sense is that the ISC is supposed to adjust the idle to 750rpm regardless of the BISS (to some extent). It's not doing this. This either means the ISC is not doing its job, or it's at the end of its range and can't open it up any more to increase idle. The BISS just gets the idle airflow in the ballpark for the ISC. What am I missing?

Which I told him how to test. See post number 4.

 

[kenamond]

Which I told him how to test. See post number 4.

The quotes were messed up in that post, so I didn't read it all. I wouldn't suspect the BISS solution until he knows the ISC is functioning properly. It might be that he's slowly wandered in his idle over the years and finally maxed out the ISC coincidentally when he did the starter, but I think other things are more likely. So I agree with checking the ISC, but I want the OP to realize that he should do that, not tinker with the BISS, which is what it looks like he was intending to do.

 

[byebye_sti]

The quotes were messed up in that post, so I didn't read it all. I wouldn't suspect the BISS solution until he knows the ISC is functioning properly. It might be that he's slowly wandered in his idle over the years and finally maxed out the ISC coincidentally when he did the starter, but I think other things are more likely. So I agree with checking the ISC, but I want the OP to realize that he should do that, not tinker with the BISS, which is what it looks like he was intending to do.

Well, to be honest with you, I really had no idea what to do. I have not done anything yet though.

But now I'm lost. WTF

So to check the ISC, I either turn on my A/C or turn on all my lights and see if the idle changes? If it does then that means that the ISC is working.

 

[SethA]

I have had this issue with my car after the battery was disconnected twice. The factory manual recommended letting the car idle for a -long- time (10min?). It had a prescribed period but I don't remember exactly how long it was (I remember it seemed excessive). In both instances I just let the car idle, it would idle very low and stalled one time but eventually figured itself out. I would try that before doing anything else.

Seth

 

[byebye_sti]

I have had this issue with my car after the battery was disconnected twice. The factory manual recommended letting the car idle for a -long- time (10min?). It had a prescribed period but I don't remember exactly how long it was (I remember it seemed excessive). In both instances I just let the car idle, it would idle very low and stalled one time but eventually figured itself out. I would try that before doing anything else.

Seth

I guess driving it around wouldn't count as 'just idling'.

I'll give that a try first.

Still waiting to hear about the ISC ordeal.

 

[kenamond]

I guess driving it around wouldn't count as 'just idling'.

I'll give that a try first.

Still waiting to hear about the ISC ordeal.

I'd try what SethA suggested. It's easy. If it fixes it or not, post back.

The ECU is supposed to automatically adjust the idle via the ISC. It is a stepper motor that plunges/retracts a needle to let more/less air past the throttle plate at idle. The ECU knows the RPM and knows that you're at idle and tells the ISC to go one way or the other if the idle is out of spec. If you turn on/off the A/C or lights or turn up/down the stereo to change the load on the accessory belts (AC compressor, alternator, power steering pump) the ECU will detect the resulting change in idle and adjust the ISC. I didn't realize that the ECU took 10 minutes to do whatever it is that SethA is talking about, because the ECU does it constantly on a normally operating motor...but maybe there's a special calibration step or something after the ECU is reset (if you leave the power off for ~10 minutes, the ECU "forgets" all of the tweaks it learned).

So the ISC test was to change the accessory load on the motor and see if the idle changed (got worse/better). If the idle doesn't self-correct, the ISC is not doing its job for some reason.

The ISC has a limited range. If it's at the "wide open" part of its range and it's still idling too low, the ISC can't go any farther. This could be because the BISS is not letting enough air through. But you didn't have a problem with idle before, so I don't expect a BISS adjustment to be the solution...but it might be.

So you can do what SethA said or do the ISC test. If the ISC doesn't seem to be working, then you move on to the next steps...it might be the ISC itself or something else.

 

[byebye_sti]

I'd try what SethA suggested. It's easy. If it fixes it or not, post back.

The ECU is supposed to automatically adjust the idle via the ISC. It is a stepper motor that plunges/retracts a needle to let more/less air past the throttle plate at idle. The ECU knows the RPM and knows that you're at idle and tells the ISC to go one way or the other if the idle is out of spec. If you turn on/off the A/C or lights or turn up/down the stereo to change the load on the accessory belts (AC compressor, alternator, power steering pump) the ECU will detect the resulting change in idle and adjust the ISC. I didn't realize that the ECU took 10 minutes to do whatever it is that SethA is talking about, because the ECU does it constantly on a normally operating motor...but maybe there's a special calibration step or something after the ECU is reset (if you leave the power off for ~10 minutes, the ECU "forgets" all of the tweaks it learned).

So the ISC test was to change the accessory load on the motor and see if the idle changed (got worse/better). If the idle doesn't self-correct, the ISC is not doing its job for some reason.

The ISC has a limited range. If it's at the "wide open" part of its range and it's still idling too low, the ISC can't go any farther. This could be because the BISS is not letting enough air through. But you didn't have a problem with idle before, so I don't expect a BISS adjustment to be the solution...but it might be.

So you can do what SethA said or do the ISC test. If the ISC doesn't seem to be working, then you move on to the next steps...it might be the ISC itself or something else.

Okay, I will go let my car run for 10 mins or so then see what happens.

So far, the idle was only acting up when I drove it.

I'll let it run, then take it for a drive and I'll let you guys know.

Be back in about 15!

 

[byebye_sti]

Okay, so I let the car sit for about 10-15 minutes just idling.

When I go back out there, I get in and it's idling nicely at 750ish rpms.

So the big test comes, take it for a drive. Right away I noticed a difference, and it was driving a lot better than before.

It was idling a bit high though, at some points it was idling at 1500rpms when the clutch was engaged.

I tested it out a bunch of times to see if the car would stall and it never did. When I got back to my house I let the car sit for a bit and it stayed idling at like 1300rpms.

When I turned on the A/C the rmps rose and when I turned on the heat the rpms dropped to about 750-1000rpms.

Any input?

 

[super97gst]

Okay, so I let the car sit for about 10-15 minutes just idling.

When I go back out there, I get in and it's idling nicely at 750ish rpms.

So the big test comes, take it for a drive. Right away I noticed a difference, and it was driving a lot better than before.

It was idling a bit high though, at some points it was idling at 1500rpms when the clutch was engaged.

I tested it out a bunch of times to see if the car would stall and it never did. When I got back to my house I let the car sit for a bit and it stayed idling at like 1300rpms.

When I turned on the A/C the rmps rose and when I turned on the heat the rpms dropped to about 750-1000rpms.

Any input?

as was mentioned before, to let your car idle for a while first. every time i disconnect the battery in mine it does this same thing. i usually have to drive mine around for a couple of days until it finally corrects itself. but it does the same thing, dies at all stop signs and lights, or at least idles down really low.

if this ends up not fixing your problem you need to test the ISC motor. you will need a multimeter to do that. the ISC is on the bottom side of the throttle body pointing toward the battery. you'll have to get underneath the upper intercooler pipe to get at it. its kind of a pain. just unplug the ISC connector, then look at the pins inside the ISC itself. there will be 6 or them. 3 pins in 2 rows. put your multimeter on ohms and put one lead on the center pin on the top row and the other on the pin on one side. it should test 28-33ohms, i have seen them test a little higher and there not be a problem with them though. you will be taking 4 different tests on the ISC. each time you will leave one lead on your multimeter on the center pin and test the pin to either side, taking a reading from each side. do the same thing to the bottom row and you've got 4 tests. if any one of them tests out of the specified range, replace the ISC motor. the ISC motor is actually just 4 independent coils working one plunger type motor.

there is also a possibility it could be the fuel pressure solenoid. its a sensor that most people tie into for their boost guage. the vaccuum hoses running out of the afpr and one out of the intake manifold run to it. with an electrical connector on one end of it. anyways, that was the first thing i had to do to my gst when i bought it several years ago. it made the idle do the exact same thing. if you are getting a CEL have the codes pulled off of it. it will tell you if the fuel pressure solenoid is acting up. hope that helps you out.

btw, the relearn time for the ecu after the battery has been disconnected can be cut way down if you clean the ISC inner passages in the throttle body.

Blake