1G another idle thread

[93AWDDSM]

I'm completely tired of this ridiculous idle. First, the car idles at 2500-2800 @ cold for about 3-4 minutes until the FIAV spring closes and the idle lowers down to 1100-1400.

Checked:
ISC
TPS (Adjusted per Vfaq)
No leaks @ TB
FIAV screw is all way in OR stuck and I couldn't budge it


The only thing I can think of to do at this point is to get the FIAV bypass plate? or pull the Throttle body again and soak the FIAV adjustment screw?

Thanks.

 

[Blu92]

I'm having a similar issue same symptoms.I tested my idle position switch and it didn't have continuity to ground when the throttle plate is shut. It could be your issue. I'm going to try and adjust mine today.

 

[blktalon3]

Fiav adj screw? You mean the biss? If the biss is stuck you gonna have to get it unstuck if you want it to idle properly.

 

[1990TSIAWDTALON]

I believe he is talking about the FIAV blockoff mod where you basically screw it all the way in and closes it off completely.

 

[steve]

TPS (Adjusted per Vfaq)

What is the output voltage with the throttle closed, and are you sure it's really closed?

Does your ISC work?
Where is the BISS adjusted to?

 

[93AWDDSM]

I'm having a similar issue same symptoms.I tested my idle position switch and it didn't have continuity to ground when the throttle plate is shut. It could be your issue. I'm going to try and adjust mine today.

- Mine has continuity and is connected.

Thanks for the replies. I'm trying to get this all prepped now because I have emissions testing in a month.

What is the output voltage with the throttle closed, and are you sure it's really closed?

Does your ISC work?
Where is the BISS adjusted to?

Per the Vfaq - with the multi meter I tested resistance between 1,2 and 4 pins seem to check out (.96 closed and it changed with increase in the throttle plate to 4.96) but I haven't checked for voltage for Closed/WOT voltage - - - > http://www.plymouthlaser.com/tps.htm

****I also had to adjust the TPS all the way counter clockwise to reach .9k ohm @ closed throttle plate****

ISC works and resistance tested OK (I went to set the idle and when I grounded the ISC out with the alligator clips, I got the idle to balance around 850-950 but once I disconnected the clips it returned to hectic idle)
BISS is bottomed out.

I believe he is talking about the FIAV blockoff mod where you basically screw it all the way in and closes it off completely.

Yes, I was talking about this - FIAV screw that closes it completely off.

 

[steve]

I haven't checked for voltage yet as the TB was off the car yesterday.
ISC works and resistance tested OK (I went to set the idle and when I grounded the ISC out with the alligator clips, I got the idle to balance around 850-950 but once I disconnected the clips it returned to hectic idle)
BISS is bottomed out.

Stock ECU?

Clearly there is air coming from somewhere it shouldn't. I found that the BISS seems to be originally designed to be 1.5 to 2 turns from bottomed out at idle much like old carb adjustment screws.
FIAV may be the problem but you need to check the EGR, Injector Insulators, PCV valve, Throttle cable adjustment, Intake Manifold gasket, Throttle Body Gaskets, Vacuum hoses, etc.

Is it surging? If not, it would imply that the Idle Position Switch isn't reading correctly.

 

[93AWDDSM]

The ecu is not the stock one - it's from another stock 1G vehicle though. EGR is removed and blocked. Throttle cable is good.

I have between 18-20 Hg when idling, is this consistent with a boost leak?

*No, it's not surging.

I can pull up to a light, be at 1400 idle and go to next light and the idle will be down to 1100 or sometimes 1000 but can change with each light/ distance. (Possibly the IPS not working? even though it gets continuity?)

 

[Victor1]

Similar issue here found it was a boost leak from an intercooler crack e

 

[dsmotors95]

I had same problem and my tps was good and i tested my iac valve and it was within spec..i replaced iac anyways and it fixed my idle problem. They're cheap off rockauto.

 

[93AWDDSM]

I had same problem and my tps was good and i tested my iac valve and it was within spec..i replaced iac anyways and it fixed my idle problem. They're cheap off rockauto.

Are you talking about the ISC? - If so, I'll swap my ISC quick after work with a working one from my brothers 1G

 

[steve]

The ecu is not the stock one - it's from another stock 1G vehicle though. EGR is removed and blocked. Throttle cable is good.

I have between 18-20 Hg when idling, is this consistent with a boost leak?

*No, it's not surging.

I can pull up to a light, be at 1400 idle and go to next light and the idle will be down to 1100 or sometimes 1000 but can change with each light/ distance. (Possibly the IPS not working? even though it gets continuity?)

I asked about Stock ECU because unless you have DSMLink or software that changes the idle speed the ECU will attempt to maintain a 750 +- 50 RPM idle at operating temp. I was trying to find out if you had changed the target idle speed and possible the decel/coasting fuel cutoff values.

Leaks that can cause idle issues aren't all boost leaks. We are talking about very small amounts of extra air reaching the cylinders. Think about how much the idle speed changes with just adjusting the BISS or just cracking open the throttle. You still will have vacuum at idle but it might be hair lower than it would be if you were idling at 750 rpm. The factory that builds the Throttle Bodies uses a sealant around the edges of the butterfly to fill the small gaps that can cause high idle. Changes in the air bypassing the butterfly aren't boost leaks and won't show up doing a BLT. Looping the nipples on the TB aren't boost leaks but can allow air from one side of the butterfly to reach the other side.

One thing I often forget is that leaning out the AFR can also cause the engine speed to rise and making sure there are no external air leaks past the MAF will address that.

Are you checking the IPS continuity at the ECU pin, are you measuring the voltage at the IPS pin with the ECU turned on? You should see continuity to chassis ground at the ECU IPS pin when the throttle is closed and an open circuit a soon as the throttle is cracked. With the ECU on you should see about 0v at the IPS pin (with the green IPS wire attached) and 5v or more when the throttle is cracked.

People are often missing the TB ground strap which grounds the IPS so it can pull the signal from the ECU low when the throttle is closed. If the ECU doesn't see the throttle closed it won't manage the idle speed and won't test for the decel/coasting fuel cutoff that "causes" idle surging.

 

[93AWDDSM]

I asked about Stock ECU because unless you have DSMLink or software that changes the idle speed the ECU will attempt to maintain a 750 +- 50 RPM idle at operating temp. I was trying to find out if you had changed the target idle speed and possible the decel/coasting fuel cutoff values.

Leaks that can cause idle issues aren't all boost leaks. We are talking about very small amounts of extra air reaching the cylinders. Think about how much the idle speed changes with just adjusting the BISS or just cracking open the throttle. You still will have vacuum at idle but it might be hair lower than it would be if you were idling at 750 rpm. The factory that builds the Throttle Bodies uses a sealant around the edges of the butterfly to fill the small gaps that can cause high idle. Changes in the air bypassing the butterfly aren't boost leaks and won't show up doing a BLT. Looping the nipples on the TB aren't boost leaks but can allow air from one side of the butterfly to reach the other side.

One thing I often forget is that leaning out the AFR can also cause the engine speed to rise and making sure there are no external air leaks past the MAF will address that.

Are you checking the IPS continuity at the ECU pin, are you measuring the voltage at the IPS pin with the ECU turned on? You should see continuity to chassis ground at the ECU IPS pin when the throttle is closed and an open circuit a soon as the throttle is cracked. With the ECU on you should see about 0v at the IPS pin (with the green IPS wire attached) and 5v or more when the throttle is cracked.

People are often missing the TB ground strap which grounds the IPS so it can pull the signal from the ECU low when the throttle is closed. If the ECU doesn't see the throttle closed it won't manage the idle speed and won't test for the decel/coasting fuel cutoff that "causes" idle surging.

I didn't even check for small gaps around the Throttle plate, but I will after work.
my MAF does have the lower honeycomb removed I noticed yesterday also (lean?). There is another MAF laying around with both honeycombs, might as well try that also.
I'll check the IPS with continuity tonight.

 

[steve]

Per the Vfaq - with the multi meter I tested resistance between 1,2 and 4 pins seem to check out (.96 closed and it changed with increase in the throttle plate to 4.96) but I haven't checked for voltage for Closed/WOT voltage - - - > http://www.plymouthlaser.com/tps.htm

****I also had to adjust the TPS all the way counter clockwise to reach .9k ohm @ closed throttle plate****

The VFAQ is wrong and doesn't take in all the factors involved, it's mainly luck that for him that worked out to the factory specified 0.50v +- 0.02v output.

 

[93AWDDSM]

The VFAQ is wrong and doesn't take in all the factors involved, it's mainly luck that for him that worked out to the factory specified 0.50v +- 0.02v output.

Glad you clarified that! so when I check the TPS today, what voltage am I looking for .48-.50 for closed Throttle plate? (it says counter-clockwise lowers voltage and clockwise increases voltage output BUT mine is completely maxed out counter-clockwise )

 

[dsmotors95]

Are you talking about the ISC? - If so, I'll swap my ISC quick after work with a working one from my brothers 1G

its the same thing

 

[pauleyman]

If you ever have an idle over 1500 something isnt right with the idle position circuit/switch.

 

[Lou98GSX]

Don't know if your problem is the same as what i had but my problem was a high idle at start up . I have a first gen throttle body with the fiav still in place not blocked off . so after having this problem for awhile i found a tip from road race engineering on how to fix this problem . I had to remove the throttle body and take out this metal plug that exposed this valve which is the fiav valve . what i did next was to turn the valve counter clockwise 1/2 a turn so the valve lets less are to bypass it which in turn lowers the idle . I put the throttle body back on and it worked great. In your case it sounds like its more of an intermittent problem so you have to check your tps , iac motor vacuum leaks and also not having the honeycombs in that mass air could also create problems if its not tuned properly .

 

[Victor1]

Also no one i see mentioned it yet but a pulled throttle cable also is a known issue after warm up itll tense up the cable

 

[steve]

Also no one i see mentioned it yet but a pulled throttle cable also is a known issue after warm up itll tense up the cable

Good Point See post 7.
Proper adjustment of the throttle cable provides slack so that the throttle isn't pulled open when things are hot.

 

[93AWDDSM]

Haven't checked anything as of yet. I will be doing some testing today. Can the Coolant temp sensor going bad cause higher idle as well when warm?