different idle issue

Y

yakini

New Member

Oct 25, 2004

28

0

0

May 9, 2005

#1

• May 9, 2005

• #1

87 stock LX with no major issues. I have read and read about idle problems on these and most are easy fixes. Mine is different and I am not 100% sure there is something wrong, but whats its doing doesnt seem right. Idle is set to about 800, car starts fine, warms up at about 1400. If I start driving and get on it a little bit, occasionaly when I pull up to a light, the idle gets hung up and like 1100. it eventually goes down where its supposed to but it really takes it anywhere from 10 to 30 seconds. even revving the engine or turning it off and restarting it doesnt help, its like the cp doesnt know its already warm. never drops low or dies, but ths hang up happens often enough that it bothers me. I have replaced the IAC twice to make sure, and installed new tps which I set the closest I could get it .94. new upper intake gasket which I thought would really be the problem but it still hasn't gone away. about the only thing I haven't touched was the egr valve but that doesn't make sense to me. I have looked long and hard for a vacuum leak (besides the intake) and cannot find a single one. So now what?????

 

_jb_

New Member

Mar 4, 2004

808

0

0

Michigan, Berrien County

May 9, 2005

#2

• May 9, 2005

• #2

I took my car out for the first time yesterday and it was idleing around 1200 for about 30 seconds too. I had forgot to connect my PCV back up and that made it run a lot better. Maybe a new PCV?

Do you hear any "shhhhhhh" sound when you turn it off? I know you said you checked for vacuum leaks, but I'm just wondering.

 

Y

yakini

New Member

Oct 25, 2004

28

0

0

May 10, 2005

#3

• May 10, 2005

• #3

actually, the pcv was changed as well as a new screen and grommet. I had considered that too.

 

T

TheUser

Active Member

Jul 25, 2003

1,859

1

36

Springfield, MO

May 10, 2005

#4

• May 10, 2005

• #4

well, if you think it's the computer thinking it's not warmed up yet, that would mean the Engine Coolant Temperature (ECT) sensor is faulty. You could try replacing that. I'm kinda wondering why it warms up at 1400 in the first place. I have a 1990 bone stock 5.0 and it warms up at like 700. The car should warm up where the base idle is set, I believe.

 

HISSIN50

"How long does it take to get help in here?

15 Year Member

Nov 29, 1999

31,179

33

129

May 10, 2005

#5

• May 10, 2005

• #5

the IAC will open to 100% duty cycle upon cold start up. this typically raises the cold idle several hundred RPM; it will idle down after 30-120 seconds (when the HEGO's light off). at this point the puter works with the lambdas to trim the A/F, even though the car is still is open loop.

a stockish motor should pull nearly 20" hg at idle on a warm motor.

you are right - EGR is the wrong way to look, IMHO. EGR does not work at idle - if it malfunctioned and did work at idle, the idle would degrade or stall.

your symptoms sound like CLASSIC vacuum leak to me. it can be a real PITA to find those leaks. the first two hoses i check are the aforementioned PCV and the charcoal cannister hose off the front of the plenum.

good luck.

 

Y

yakini

New Member

Oct 25, 2004

28

0

0

May 10, 2005

#6

• May 10, 2005

• #6

HIsSIn, heres my next question. Should the car idle when warm if u disconnect the IAC? I thought that it should and I disconnected it, the idle dropped until the car died. So then I figured maybe the idle was set so low that the IAC was in constant use just to keep the car running, I thought this might explain the different RPMS. I finally get it adjusted where the car sits at 750-800 when it finally settles all the way down. I pull the IAC plug and bam, dead again. I also noticed lately when I start the car and it is already warmed up the idle goes immediatly to 1000 or so then drops low, so low that it almost dies, then back up to normal. after that it is fine. I am lost, but I will check all vaccum related lines again, thanks for the help.

 

D

D347643

Banned

Jan 28, 2003

1,095

0

0

portland, OR

May 10, 2005

#7

• May 10, 2005

• #7

you smoke cigs? cheap alt to smoke machine. can work wonders if you get a few friends together.

 

Y

yakini

New Member

Oct 25, 2004

28

0

0

May 10, 2005

#8

• May 10, 2005

• #8

D347643 said:

you smoke cigs? cheap alt to smoke machine. can work wonders if you get a few friends together.

Click to expand...

?????????????????????????????????????smoke machine????????????

 

HISSIN50

"How long does it take to get help in here?

15 Year Member

Nov 29, 1999

31,179

33

129

May 10, 2005

#9

• May 10, 2005

• #9

yakini said:

HIsSIn, heres my next question. Should the car idle when warm if u disconnect the IAC? I thought that it should and I disconnected it, the idle dropped until the car died. So then I figured maybe the idle was set so low that the IAC was in constant use just to keep the car running, I thought this might explain the different RPMS. I finally get it adjusted where the car sits at 750-800 when it finally settles all the way down. I pull the IAC plug and bam, dead again. I also noticed lately when I start the car and it is already warmed up the idle goes immediatly to 1000 or so then drops low, so low that it almost dies, then back up to normal. after that it is fine. I am lost, but I will check all vaccum related lines again, thanks for the help.

Click to expand...

YAkINi, people have managed to come up with many idle setting procedures. I like to set the warm idle (with no load) with the IAC disconnected. this makes sense and helps if the IAC goes south. when done correctly, the idle should not increase significantly once the IAC is connected, if everything is in proper order.

I would start over at the top and reset stuff - dont forget to at least check the TPS once you play with the idle set screw. one can have the idle set screw off and then all other sensors and the puter go nuts trying to get the idle back down to the 625-750 RPM spec.

I would note that bad timing or even lambdas can cause idle hunting.

good luck with it.

 

HISSIN50

"How long does it take to get help in here?

15 Year Member

Nov 29, 1999

31,179

33

129

May 10, 2005

#10

• May 10, 2005

• #10

oh yeah, here is some info on setting the idle (just to see how it sounds compared to your sources).

good luck.

 

D

D347643

Banned

Jan 28, 2003

1,095

0

0

portland, OR

May 10, 2005

#11

• May 10, 2005

• #11

yeah to check for vac leaks
if smoke is blown into the intake stream. WITH ENGINE OFF you will see where the smoke comes out via vac leak.

 

Y

yakini

New Member

Oct 25, 2004

28

0

0

May 10, 2005

#12

• May 10, 2005

• #12

D347643 said:

yeah to check for vac leaks
if smoke is blown into the intake stream. WITH ENGINE OFF you will see where the smoke comes out via vac leak.

Click to expand...

O, I didn't catch that the first time, thanks.

 

Y

yakini

New Member

Oct 25, 2004

28

0

0

May 10, 2005

#13

• May 10, 2005

• #13

Thank you Hissin, I am going to do what u suggest and try starting over to eliminate this stuff. Like I said, it dies with the IAC unplugged so based off what you said, something could be set way off.

 

Y

yakini

New Member

Oct 25, 2004

28

0

0

May 11, 2005

#14

• May 11, 2005

• #14

with engine off?? what if the leak is far from the intake, wouldnt you need the engine on to pull the smoke through.

 

89roadster

Founding Member

Apr 19, 1999

1,124

0

0

Kent Island, MD

May 11, 2005

#15

• May 11, 2005

• #15

To check for vacuum leaks, try spraying (lightly) carb cleaner around the hoses with the engine running. If you hear the engine rev, try it again, if it happens in the same area the second time - there's your leak - just be careful and have a fire extinquisher handy (hasn't happened yet, but you're playing with flammable liquid).