Idle issue

dirocyn · 09-01-2009, 12:59 PM

All right, I've got a problem fixed, (I think), I want to know if y'all think I've found the right problem. A couple weeks ago, I took my Two to another city an hour away, 70 mph interstate trip. Temp gauge stayed normal the whole trip. When I got back into my own town, I noticed the idle was different. It was idling around 1500, except it would occasionally dip down to about 1200. I intended to pop the engine cover and look as soon as I got home, but I was wearing the wrong clothes for engine work--so some time passed. Last Friday the idle changed again, this time up to about 2000. The idle-drops became more frequent, started following a definite pattern--about once every 5 seconds. Today was a day off, so I decided I'd change the oil, hunt for whatever vac line's busted, and see if I could remove any air from the cooling system. I did notice if I unplug the tps, the idle-drops stop--but the rpms go up to about 2200. I cleaned the plug at the tps, no difference. Idle adjust screw is all the way in (slow)--it was like that before.

I can't find any vac lines off, and I can't hear any hiss other than the sound of the belts going round.

Burped the cooling system--I have a question about that I'll put in a separate post. Didn't seem to make any diff as far as the idle issues go.

Just to check the vac, I pulled off the vac line that goes to--I guess that's the auxiliary air valve (it's right under the tps). At this point I guess I should mention, this car is an 86, normally aspirated. Engine immediately died. Pushed the vac line back on, cranked again, and this time pinched the line--and the engine slowed down. Traced the vac line back to some sort of sensor (BGB doesn't seem to mention it, but the BGB says 1988, perhaps that's why). Whatever that sensor is, it's located on the driver's side frame, right between the relay/fuse box and the strut tower. It's got a spring-loaded adjuster wheel, and a two-wire electrical connector. Turned the adjuster and my idle speed responded, adjusted all the way in I've got idle at about 900. The idle is steady, not cycling anymore. So, problem solved, I guess.

Now I get to the question--what the heck was I just adjusting? And is this a thing that can go out of whack by itself? Or have I still got a problem somewhere else?

Dave In Indy · 09-01-2009, 01:14 PM

What you were adjusting was the idle up for the AC system. It's designed to increase the idle to compensate for the increased drag on the motor when the AC compressor is running. That is why your idle changed when you adjusted it. As far as the idle issue you are having, check your diagnostic codes and see what shows up.

dirocyn · 09-01-2009, 02:15 PM

Hey, thanks, I never would have thought to look at air conditioner stuff, but that's exactly what it is. The AC hasn't ever worked while I've had the car, and I don't think I turned it on. But I went and checked, someone had turned the "economy" switch on. Probably one of my kids. Turn off the AC and the idle goes back where it's supposed to be.

That's one mystery solved.

The bouncing idle was probably caused by the engine reading 2000 rpms and the tps saying it's at idle. Excellent good, and another problem solved.

As an additional bonus, I now know I can set two separate idle speeds, and switch between them with the touch of a button on the dash. When I teach my wife to drive stick, you better believe I'm gonna set the AC Idle right back at 2000. Well, maybe 1800, and avoid the bouncy idle. Sweet.

Dave In Indy · 09-01-2009, 08:34 PM

I just removed the hoses and put vacuum plugs on where the hoses attach to the engine. Problem solved even if someone does press the button.

jsnod25 · 10-02-2009, 01:10 PM

it doesnt seem like that should have raised your idle, unless the AC was on, even then it shouldnt raise it to 2000... but i guess if its fixed, then good on yah. I have a similar problem but its not being fixed by any of the above mentioned fixes... I have TPS all the way down, i have changed the oil, oil filter, ran BG 44k to clean the injectors, changed the air filter, and tried to clean my MAF but broke it.... i still dont know if that was the problem yet untill i get a new MAF... anyways, mine will rise to 2000, and can drop all the way down to 450, at which point i DO turn on the AC so that it will bring it back up to 950/1000 but then a couple stops later it could be at 1500 so i have to turn AC off to drop it back to 1000

09-01-2009, 12:59 PM	#1 (permalink)
dirocyn Cage Fighter Join Date: Mar 2009 Location: Murfreesboro, TN Posts: 1,178 Thanks: 14 Thanked 110 Times in 108 Posts iTrader Rating: (0/0% )	Idle issue All right, I've got a problem fixed, (I think), I want to know if y'all think I've found the right problem. A couple weeks ago, I took my Two to another city an hour away, 70 mph interstate trip. Temp gauge stayed normal the whole trip. When I got back into my own town, I noticed the idle was different. It was idling around 1500, except it would occasionally dip down to about 1200. I intended to pop the engine cover and look as soon as I got home, but I was wearing the wrong clothes for engine work--so some time passed. Last Friday the idle changed again, this time up to about 2000. The idle-drops became more frequent, started following a definite pattern--about once every 5 seconds. Today was a day off, so I decided I'd change the oil, hunt for whatever vac line's busted, and see if I could remove any air from the cooling system. I did notice if I unplug the tps, the idle-drops stop--but the rpms go up to about 2200. I cleaned the plug at the tps, no difference. Idle adjust screw is all the way in (slow)--it was like that before. I can't find any vac lines off, and I can't hear any hiss other than the sound of the belts going round. Burped the cooling system--I have a question about that I'll put in a separate post. Didn't seem to make any diff as far as the idle issues go. Just to check the vac, I pulled off the vac line that goes to--I guess that's the auxiliary air valve (it's right under the tps). At this point I guess I should mention, this car is an 86, normally aspirated. Engine immediately died. Pushed the vac line back on, cranked again, and this time pinched the line--and the engine slowed down. Traced the vac line back to some sort of sensor (BGB doesn't seem to mention it, but the BGB says 1988, perhaps that's why). Whatever that sensor is, it's located on the driver's side frame, right between the relay/fuse box and the strut tower. It's got a spring-loaded adjuster wheel, and a two-wire electrical connector. Turned the adjuster and my idle speed responded, adjusted all the way in I've got idle at about 900. The idle is steady, not cycling anymore. So, problem solved, I guess. Now I get to the question--what the heck was I just adjusting? And is this a thing that can go out of whack by itself? Or have I still got a problem somewhere else?

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09-01-2009, 01:14 PM	#2 (permalink)
Dave In Indy Some Skills Join Date: Jun 2009 Posts: 61 Thanks: 1 Thanked 3 Times in 3 Posts iTrader Rating: (0/0% )	What you were adjusting was the idle up for the AC system. It's designed to increase the idle to compensate for the increased drag on the motor when the AC compressor is running. That is why your idle changed when you adjusted it. As far as the idle issue you are having, check your diagnostic codes and see what shows up.

09-01-2009, 02:15 PM	#3 (permalink)
dirocyn Cage Fighter Join Date: Mar 2009 Location: Murfreesboro, TN Posts: 1,178 Thanks: 14 Thanked 110 Times in 108 Posts iTrader Rating: (0/0% )	Hey, thanks, I never would have thought to look at air conditioner stuff, but that's exactly what it is. The AC hasn't ever worked while I've had the car, and I don't think I turned it on. But I went and checked, someone had turned the "economy" switch on. Probably one of my kids. Turn off the AC and the idle goes back where it's supposed to be. That's one mystery solved. The bouncing idle was probably caused by the engine reading 2000 rpms and the tps saying it's at idle. Excellent good, and another problem solved. As an additional bonus, I now know I can set two separate idle speeds, and switch between them with the touch of a button on the dash. When I teach my wife to drive stick, you better believe I'm gonna set the AC Idle right back at 2000. Well, maybe 1800, and avoid the bouncy idle. Sweet.

09-01-2009, 08:34 PM	#4 (permalink)
Dave In Indy Some Skills Join Date: Jun 2009 Posts: 61 Thanks: 1 Thanked 3 Times in 3 Posts iTrader Rating: (0/0% )	I just removed the hoses and put vacuum plugs on where the hoses attach to the engine. Problem solved even if someone does press the button.

10-02-2009, 01:10 PM	#5 (permalink)
jsnod25 How did this get changed? Join Date: Sep 2009 Location: Va beach, va Posts: 133 Thanks: 6 Thanked 0 Times in 0 Posts iTrader Rating: (0/0% )	it doesnt seem like that should have raised your idle, unless the AC was on, even then it shouldnt raise it to 2000... but i guess if its fixed, then good on yah. I have a similar problem but its not being fixed by any of the above mentioned fixes... I have TPS all the way down, i have changed the oil, oil filter, ran BG 44k to clean the injectors, changed the air filter, and tried to clean my MAF but broke it.... i still dont know if that was the problem yet untill i get a new MAF... anyways, mine will rise to 2000, and can drop all the way down to 450, at which point i DO turn on the AC so that it will bring it back up to 950/1000 but then a couple stops later it could be at 1500 so i have to turn AC off to drop it back to 1000