car does not want to idle. and weird wot spark adv. need help
09-03-2009, 05:44 PM
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car does not want to idle. and weird wot spark adv. need help My car, built 93 trans am. does not want to idle. esp. when cold. but it seems to be getting worse. it's okay until you come up to a stop and it wants to die out, unless you feather the throttle. and the car seems to be surging even w/the 3800 stall.
It seems when I 1st. got the car about 2 weeks ago it idled high, but didn't want to die, I took off the t.b. and cleaned it up really good w/t.b. cleaner, then it acted funky, the idle went to normal 850rpms but didn't want to really idle. I checked for vac leaks and there isn't any. I figured I clogged up the iac valve. so I took it off the other day and cleaned it, but it didn't help.so I bought a scanner and here are some readings if anybody sees a problem can they help.
OH YEAH. I do have the check eng. light out, from no cats/egr. would it still throw a code? It's not throwing anything on my auto xray scanner. here are the scanner readings below.
MAP sens:2.62-2.78 volts. Idling it was fluctuating. 4.64V key on,eng off.
IAC motor pos. 157-160 steps. reving up no diff. wot 90 steps. seems weird.
tps: idle-.54v.... then eng. off key on: .54v...and 4.21v= wot
02's were switching quickly,both sides. seem to be working.
Left block learn 149-152 idling. same for right block learn.
block learn cell: 16 at idle.
throttle 0% idle. 99% wot.
left integrator value. 116-140 idle. hanging around 130's.
right integrat value. same.
spark advance. 25-30* at idle. fluctuating.
now this is weird.. 36-38* at wot. going down road. seems high.
Learned idle pos. 32 setps at idle.
all readings running in closed loop.
I know it's long, but if anybody can help I would really appreciate it.
and does anybody know of a good LT1 website. thanks...
It seems when I 1st. got the car about 2 weeks ago it idled high, but didn't want to die, I took off the t.b. and cleaned it up really good w/t.b. cleaner, then it acted funky, the idle went to normal 850rpms but didn't want to really idle. I checked for vac leaks and there isn't any. I figured I clogged up the iac valve. so I took it off the other day and cleaned it, but it didn't help.so I bought a scanner and here are some readings if anybody sees a problem can they help.
OH YEAH. I do have the check eng. light out, from no cats/egr. would it still throw a code? It's not throwing anything on my auto xray scanner. here are the scanner readings below.
MAP sens:2.62-2.78 volts. Idling it was fluctuating. 4.64V key on,eng off.
IAC motor pos. 157-160 steps. reving up no diff. wot 90 steps. seems weird.
tps: idle-.54v.... then eng. off key on: .54v...and 4.21v= wot
02's were switching quickly,both sides. seem to be working.
Left block learn 149-152 idling. same for right block learn.
block learn cell: 16 at idle.
throttle 0% idle. 99% wot.
left integrator value. 116-140 idle. hanging around 130's.
right integrat value. same.
spark advance. 25-30* at idle. fluctuating.
now this is weird.. 36-38* at wot. going down road. seems high.
Learned idle pos. 32 setps at idle.
all readings running in closed loop.
I know it's long, but if anybody can help I would really appreciate it.
and does anybody know of a good LT1 website. thanks...
Last edited by 06blackGTO; 09-03-2009 at 05:59 PM.
09-03-2009, 10:01 PM
#4
If your idle air controller steps are that high then you need to open your throttle blades up a little bit and then watch to see that they come back down.
If your block learns are in the 150's you are lean and you need to add fuel to the ve tables around where you idle. This would most especially show up when the car is cold and in open loop. The only other possibility is some sort of a leak in the exhaust or bad o2 sensors.
36-38 degrees of timing at wot is perfectly fine and good in fact. Can be as much as 45 degrees going down the road but the lt1 doesn't usually need that much cruising and it can get you knock retard.
The idle timing fluttering is perfectly normal unless you program it out. The lt1 uses two things to control the idle speed with one being obvious the iac motor, and two being ignition timing which is the finer and faster adjustment the pcm can make to stay on target idle.
If your block learns are in the 150's you are lean and you need to add fuel to the ve tables around where you idle. This would most especially show up when the car is cold and in open loop. The only other possibility is some sort of a leak in the exhaust or bad o2 sensors.
36-38 degrees of timing at wot is perfectly fine and good in fact. Can be as much as 45 degrees going down the road but the lt1 doesn't usually need that much cruising and it can get you knock retard.
The idle timing fluttering is perfectly normal unless you program it out. The lt1 uses two things to control the idle speed with one being obvious the iac motor, and two being ignition timing which is the finer and faster adjustment the pcm can make to stay on target idle.
09-03-2009, 10:31 PM
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09-03-2009, 10:33 PM
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If your idle air controller steps are that high then you need to open your throttle blades up a little bit and then watch to see that they come back down.
ANSWER: I'll try that tomorrow. problem did not show up until I took off the t.b. and cleaned it up. I did the iac test per shbox. and it was within range.
53ohms. per side.I did learn that you can reset the iac. and I'll try it in the morning.
If your block learns are in the 150's you are lean and you need to add fuel to the ve tables around where you idle. This would most especially show up when the car is cold and in open loop. The only other possibility is some sort of a leak in the exhaust or bad o2 sensors.
ANSWER: Yes the block learns are in the 145's to 150's at idle in closed loop.
the header gaskets are leaking on each side. damn copper gaskets.
I have some seal for good aluminum gaskets coming. prob. tomorrow.
The 02's show that they are switching very quickly in closed loop. So I think there working allright, and I did convert to heated when I last owned the car. It takes 2-3min. idling then it will go into closed loop.
36-38 degrees of timing at wot is perfectly fine and good in fact. Can be as much as 45 degrees going down the road but the lt1 doesn't usually need that much cruising and it can get you knock retard.
ANS: thanks for letting me know that, Hell my LS2 goat only likes 23 degrees of timing at wot.
The idle timing fluttering is perfectly normal unless you program it out. The lt1 uses two things to control the idle speed with one being obvious the iac motor, and two being ignition timing which is the finer and faster adjustment the pcm can make to stay on target idle.
ANSWER: I'll try that tomorrow. problem did not show up until I took off the t.b. and cleaned it up. I did the iac test per shbox. and it was within range.
53ohms. per side.I did learn that you can reset the iac. and I'll try it in the morning.
If your block learns are in the 150's you are lean and you need to add fuel to the ve tables around where you idle. This would most especially show up when the car is cold and in open loop. The only other possibility is some sort of a leak in the exhaust or bad o2 sensors.
ANSWER: Yes the block learns are in the 145's to 150's at idle in closed loop.
the header gaskets are leaking on each side. damn copper gaskets.
I have some seal for good aluminum gaskets coming. prob. tomorrow.
The 02's show that they are switching very quickly in closed loop. So I think there working allright, and I did convert to heated when I last owned the car. It takes 2-3min. idling then it will go into closed loop.
36-38 degrees of timing at wot is perfectly fine and good in fact. Can be as much as 45 degrees going down the road but the lt1 doesn't usually need that much cruising and it can get you knock retard.
ANS: thanks for letting me know that, Hell my LS2 goat only likes 23 degrees of timing at wot.
The idle timing fluttering is perfectly normal unless you program it out. The lt1 uses two things to control the idle speed with one being obvious the iac motor, and two being ignition timing which is the finer and faster adjustment the pcm can make to stay on target idle.
It does act like the tune is out of whack, but I'll reset the iac or open the blades alittle to see if the counts go down. and I'll put on the new header gaskets when they come in, and I'll take it from there I guess.
thanks for the help.
09-04-2009, 04:53 PM
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Well I finally fixed the problem. it was the iac valve. The pintle was stuck open and not allowing it to suck in air. After buying it 110.00 bucks and putting it on, the car idles great. and no rpm surging. I was able to cover up the little hole in each t.b. blade that I had to drill a few yrs. ago when I prev. owned the car and put on a holley 58mm. t.b. so the iac has been messed up for atleast 2-3 yrs. and I guess it finally got stuck. Now the iac hole in the t.b. is really sucking in air, and it has never done that. so all is well.
