One last bad idle thread
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From: College Station, Texas
One last bad idle thread Hey guys, I'm still having fits with trying to figure out why my 5.3 swapped firebird will randomly give me fits.
Mods:
5.3 lm7
Ls6 cam
Ls6 intake
F body harness and computer
Milled heads
2800 converter
Slp and k&n
New:
Fuel filter
Tps
Iat
PCV valve
Both o2's
Checked:
Spark plugs- ngk tr55's look good, low miles
Iac 'cleaned and tested with new one'
Clean MAF and throttle body
Good fuel pressure
Here is my problem, occasionally on cold starts, it will start right up but hold an idle near 400 rpm. It will rock, sputter, smell, and smoke. Other times it will rev up like normal, then immediately fall. Other times it will rev to 2500 and hold it for 5 seconds then fall and be normal. Sometimes it is perfect, revs to 100 then drops to 5-600 and holds it.
Sometimes it will be idling fine, but when I shift into drive or reverse, it pulls the idle down and stalls, or bounces and surges.
The car will drive fine. Even at the worst idles it still takes off normal, no sputtering or anything. Until I come to a stop. Once I get close to stopping the rpm's drop to about 400. When I come to a stop the car will either die, or rev and surge until it dies, unless I put it in neutral and hold a little gas.
Sometimes I can get it to go a few days being perfect, then it will be horrible for a few days. Then it starts getting better, but then gets a lot worse until it randomly is perfect again. It's demented.
I can find plenty of things to check, and I have checked them all. The worst part is NO CODES. And yes it has been tuned.
Any more ideas or suggestions? I can answer any questions y'all might have also.
Mods:
5.3 lm7
Ls6 cam
Ls6 intake
F body harness and computer
Milled heads
2800 converter
Slp and k&n
New:
Fuel filter
Tps
Iat
PCV valve
Both o2's
Checked:
Spark plugs- ngk tr55's look good, low miles
Iac 'cleaned and tested with new one'
Clean MAF and throttle body
Good fuel pressure
Here is my problem, occasionally on cold starts, it will start right up but hold an idle near 400 rpm. It will rock, sputter, smell, and smoke. Other times it will rev up like normal, then immediately fall. Other times it will rev to 2500 and hold it for 5 seconds then fall and be normal. Sometimes it is perfect, revs to 100 then drops to 5-600 and holds it.
Sometimes it will be idling fine, but when I shift into drive or reverse, it pulls the idle down and stalls, or bounces and surges.
The car will drive fine. Even at the worst idles it still takes off normal, no sputtering or anything. Until I come to a stop. Once I get close to stopping the rpm's drop to about 400. When I come to a stop the car will either die, or rev and surge until it dies, unless I put it in neutral and hold a little gas.
Sometimes I can get it to go a few days being perfect, then it will be horrible for a few days. Then it starts getting better, but then gets a lot worse until it randomly is perfect again. It's demented.
I can find plenty of things to check, and I have checked them all. The worst part is NO CODES. And yes it has been tuned.
Any more ideas or suggestions? I can answer any questions y'all might have also.
Launching!
Joined: Jan 2012
Posts: 216
Likes: 1
From: Davisburg, MI
If your battery is bad it might be going through a relearn on the idle air control occasionally. Is the car cranking sluggish? A bad MAF can do that if you have an opportunity to swap it with a known good one. Bunch of carbon build up in the intake and heads can cause this, but it sounds like yours are fresh.
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From: College Station, Texas
The car has been dyno tuned, and I made sure to go over this idle problem (it occurred before the tune). He hit it pretty good and it was fine for a while, but it seems like the computer re taught itself the wrong things.
I'm going to clean the MAF, and port the throttle body while I'm at it. Ill make sure the tb and iac are good and clean
I'm going to clean the MAF, and port the throttle body while I'm at it. Ill make sure the tb and iac are good and clean
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The car has been dyno tuned, and I made sure to go over this idle problem (it occurred before the tune). He hit it pretty good and it was fine for a while, but it seems like the computer re taught itself the wrong things.
I'm going to clean the MAF, and port the throttle body while I'm at it. Ill make sure the tb and iac are good and clean
I'm going to clean the MAF, and port the throttle body while I'm at it. Ill make sure the tb and iac are good and clean
Thread Starter
TECH Apprentice
iTrader: (6)
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From: College Station, Texas
Thread Starter
TECH Apprentice
iTrader: (6)
Joined: Mar 2012
Posts: 311
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From: College Station, Texas
A little update. I ported my own throttle body. Not extreme, just nicked down the lip and smoothed it all out. I also cleaned up the area that the IAC sensor sits, and rubbed the MAF with a q tip.
The car runs better. Here is how my day goes:
Morning cold starts, car is perfect. Idles high like normal and settles down when it warms up a little. Doesn't mess up when shifting out of the garage and into the street. Half a mile to the stop sign, car is a little over halfway warmed up, stops fine, idle is perfect. Another two miles to the next stop sign and it tries to idle a little low but will not buck or die. I don't have to do anything it will settle itself out. Then it's good the rest of the way to school that includes more stops. This is every morning for the last week.
Leaving school after the car sits for 6 hours, it starts and idles low but slowly raise to normal. It will smoke and smell like gas. This is only sometimes. Other times it starts fine and runs good all the way home.
But say I go to a gas station and turn it off for a few minutes, when I come to restart it, it dies immediately. Every time. Unless I rev it to 1500 and then it settles normal an is fine.
So clean the MAF more? Deal with it? Any ideas? I heard somewhere about the coolant temp sensor doing something.
The car runs better. Here is how my day goes:
Morning cold starts, car is perfect. Idles high like normal and settles down when it warms up a little. Doesn't mess up when shifting out of the garage and into the street. Half a mile to the stop sign, car is a little over halfway warmed up, stops fine, idle is perfect. Another two miles to the next stop sign and it tries to idle a little low but will not buck or die. I don't have to do anything it will settle itself out. Then it's good the rest of the way to school that includes more stops. This is every morning for the last week.
Leaving school after the car sits for 6 hours, it starts and idles low but slowly raise to normal. It will smoke and smell like gas. This is only sometimes. Other times it starts fine and runs good all the way home.
But say I go to a gas station and turn it off for a few minutes, when I come to restart it, it dies immediately. Every time. Unless I rev it to 1500 and then it settles normal an is fine.
So clean the MAF more? Deal with it? Any ideas? I heard somewhere about the coolant temp sensor doing something.
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From: College Station, Texas
So I've got an update. The tuner looked at the car the other day and went over everything. There is definitely something electrically wrong. He was having to change things he should never have to with this setup, and it's still bad. Every startup is different. It never stays constant. We logged the o2's and you can watch them go really low and stop switching.
I've pulled pins in the harness to any wires not needed to eliminate the possibility of those wires grounding out somewhere. I rechecked grounds also.
I asked about the coolant temp sensor. It was fine every day and perfect when we looked at the tune. The very next day I started to loose the readings on the dash for coolant temp. I also went into 3rd gear only limp mode with the trans.
This car is cursed. But I have to ask, any suggestions?
I've pulled pins in the harness to any wires not needed to eliminate the possibility of those wires grounding out somewhere. I rechecked grounds also.
I asked about the coolant temp sensor. It was fine every day and perfect when we looked at the tune. The very next day I started to loose the readings on the dash for coolant temp. I also went into 3rd gear only limp mode with the trans.
This car is cursed. But I have to ask, any suggestions?
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From: College Station, Texas
Changed the coolant temp sensor. Still didn't showing the dash. Limp mode still there. Codes for MAF, injector, shift solenoid, and multiple temp sensors were on
I was reading in another thread where a guy was having issues similar and his ground wasn't strong enough. I believe he said they didn't have the ground going from the battery to the block, maybe it was to the frame? He swapped it and it fixed it.
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I got it hooked back up. I re did all my grounds in new locations and it must have helped the issue.
Last edited by Y87bird00; Dec 23, 2013 at 10:56 AM.
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From: College Station, Texas
I still have the same problems. Inconsistent idle and periodic bad starts.
Somebody tell me if this sounds right:
I have three grounds on the back of the heads from the wiring harness. Two in one bolt on one head then one on the other head.
I have the battery negative cable going to the chassis in the stock location and to the block behind the a/c comp.
There is a small strap going from the chassis to the block behind the alternator (bolt that holds o2 in place) I also have a second ground going from this bolt to the chassis in a different location.
Do I need additional grounds? Or move the block-chassis grounds to separate bolts on the block? To many grounds?
Somebody tell me if this sounds right:
I have three grounds on the back of the heads from the wiring harness. Two in one bolt on one head then one on the other head.
I have the battery negative cable going to the chassis in the stock location and to the block behind the a/c comp.
There is a small strap going from the chassis to the block behind the alternator (bolt that holds o2 in place) I also have a second ground going from this bolt to the chassis in a different location.
Do I need additional grounds? Or move the block-chassis grounds to separate bolts on the block? To many grounds?
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From: College Station, Texas
For it to idle with the old throttle body being drilled it the idle tables had to be cheated just to make it idle. With the idle tables being cheated for a drilled out throttle body its NOT going to idle right with a good throttle body without the tune being fixed.