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Rough idle, dimming lights

A

AndrewM6097

CEG'er
Joined
Jan 3, 2008
Messages
131
Location
Worcester, Ma
So i've been chasing this rough idle problem for a while now. The engine dips to about 700 rpm and raises back up to normal between 5 and 10 times after coming to a stop. The car vibrates as this is happening and the lights dim quite a bit while this is happening. I've tried numerous things, like replace vaccum hoses, clean MAF sensor, ive sprayed carb cleaner to find a vaccum leak, replaced battery terminals, rotated MAF, IACV, fixed an exhaust leak, reloaded my tune, i tried stock setting on the ECU also. Nothing has changed.

I'm thinking it might be my ALT taking a dump. The "Big 3" are upgraded, and the fix for pulsing lights has been done. Could a bad alt cause a rough idle like this? Would it be worth it to pull the alt and have it bench tested? I've pulled it a few times before so its not too big of a deal.

Also the EGR system is out of the question, as it has been removed from my vehicle and my tune supports it.
 
AndrewM6097 said:
So i've been chasing this rough idle problem for a while now. The engine dips to about 700 rpm and raises back up to normal between 5 and 10 times after coming to a stop. The car vibrates as this is happening and the lights dim quite a bit while this is happening. I've tried numerous things, like replace vaccum hoses, clean MAF sensor, ive sprayed carb cleaner to find a vaccum leak, replaced battery terminals, rotated MAF, IACV, fixed an exhaust leak, reloaded my tune, i tried stock setting on the ECU also. Nothing has changed.

I'm thinking it might be my ALT taking a dump. The "Big 3" are upgraded, and the fix for pulsing lights has been done. Could a bad alt cause a rough idle like this? Would it be worth it to pull the alt and have it bench tested? I've pulled it a few times before so its not too big of a deal.

Also the EGR system is out of the question, as it has been removed from my vehicle and my tune supports it.
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no, a bad alternator has nuthn to do with your bad idle. i've had this problem for a long time. i've just got accustomed to it actually:shrug:. it also happens after some spirited acceleration and u come to a stop.
 
The car never acted this way before. The idle used to be fine, and like you stated after a sprinted run it would hunt for idle for a few seconds, but this is different. Its just very frustrating that i cant pin point the problem.
 
Curious, have you done the throttle hang fix? For my '99 CSVT I couldn't get an acceptable and consistant idle after doing the hang fix. Would do very similar to what you described. I even tried it at every hole size and then bought another cap and tried every size again. Gave up and removed it, perfect idle immediately back.

BTW my idle is always exactly a rock steady 650-700 rpm. You mentioned 700 rpm as being too low?
 
i would have to say that the low voltage is because the idle ddrops to low.

my 3L also sometime hunts alittle for idle then smooth right out. at time the voltage will drop alittle also. I do have a new IAC that I installed just before the 3L.

I heard of one case recently where the idle would continually hunt or surge because at that time a O2 sensor was cutting out so the PCM didn't know what the a/f ratio was. in my case this shouldn't be the issue as both my upper O2 sensors are new ....
 
Well maybe what i can do is hook up my snap on scanner and watch the o2 sensors as its hunting for idle. The car runs great otherwise, this is just really annoying.

I have not done the throttle hang fix so it wouldnt be that. I'll test the alt and battery tomorrow just to be sure. Another thing that came to mind is a threw a code a while ago for the MAF sensor, i dont remember exactly what it was but it hasnt come back since. I'll hit up the scrap yard tomorrow and see if i can find a used unit.
 
Don't know if this will help but when my SE had idling problems earlier this spring, my dad said it was because water was getting frozen and causing the throttle to stick. It would idle real low for a few minutes, kick up to around normal idling speed, go back down, and sometimes stall because of that. I would have to sit there for a half hour keeping the RPM's at around 1,500 -2,000 until it would un-stick itself. He showed me a trick with a screwdriver too if it took too long. Of course right now you shouldn't have issues with freezing water, but your throttle might be sticking nonetheless. Just something to look into.
 
MoonlightSE said:
Don't know if this will help but when my SE had idling problems earlier this spring, my dad said it was because water was getting frozen and causing the throttle to stick. It would idle real low for a few minutes, kick up to around normal idling speed, go back down, and sometimes stall because of that. I would have to sit there for a half hour keeping the RPM's at around 1,500 -2,000 until it would un-stick itself. He showed me a trick with a screwdriver too if it took too long. Of course right now you shouldn't have issues with freezing water, but your throttle might be sticking nonetheless. Just something to look into.
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Yeah not cold enough for ice yet, thank god. But speaking of throttle, i was looking around in the engine bay while it was idling and i unplugged the TPS. The car stumbled and i plugged it back in and then my rpms would stay around 1k and wouldnt come back down. I shut it down and restarted it and it did the same thing for a few miles down the road. It finally stopped and went back to normal. Possible TPS related problem?
 
AndrewM6097 said:
Yeah not cold enough for ice yet, thank god. But speaking of throttle, i was looking around in the engine bay while it was idling and i unplugged the TPS. The car stumbled and i plugged it back in and then my rpms would stay around 1k and wouldnt come back down. I shut it down and restarted it and it did the same thing for a few miles down the road. It finally stopped and went back to normal. Possible TPS related problem?
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i doubt it. its the TPS. of course the car will stumble if disconnected. this problem is an intermittent one. it comes and goes. i'm not eliminating the tps as a culprit. i'm just not convinced thats the issue.
 
BAD SVT said:
i doubt it. its the TPS. of course the car will stumble if disconnected. this problem is an intermittent one. it comes and goes. i'm not eliminating the tps as a culprit. i'm just not convinced thats the issue.
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well i knew it was going to stumble, but it was weird how the idle stuck after i plugged it back in. Maybe thats just what it does. I have a bunch of sensors that im gonna try out and i will post my results.
 
AndrewM6097 said:
well i knew it was going to stumble, but it was weird how the idle stuck after i plugged it back in. Maybe thats just what it does. I have a bunch of sensors that im gonna try out and i will post my results.
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sounds good. FWIW, many have this problem also. we've just learned to live with it:). but by all means, when u pinpoint the culprit, please share:)
 
BAD SVT said:
sounds good. FWIW, many have this problem also. we've just learned to live with it:). but by all means, when u pinpoint the culprit, please share:)
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Yeah i have read that a lot of people have this problem, but what bothers me is i never had it before. I am determined to figure it out :cool:
 
I know you said you cleaned the MAF, but it doesn't rule it out. Unplug the MAF and see if it drives any better. If it does, your MAF is bad.
 
Ian that reminds me of something ...


Andrew are you using a maf adaptor? I am pretty sure mine doesn't seal to the maf perfectly, hense the reson I find alittle dust in the maf when I have pulled it. maybe the sensor is getting dirty.... I know I want to add a gasket or seal it up somehow.


btw does anyone know if there is a 80 mm lightneing maf gasket for between the maf and the airbox?
 
BrApple said:
Ian that reminds me of something ...


Andrew are you using a maf adaptor? I am pretty sure mine doesn't seal to the maf perfectly, hense the reson I find alittle dust in the maf when I have pulled it. maybe the sensor is getting dirty.... I know I want to add a gasket or seal it up somehow.


btw does anyone know if there is a 80 mm lightneing maf gasket for between the maf and the airbox?
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thats true brian. i dont have any gasket @ that junction as well. neither do i know where i could get one. i'm sure there'll be a bit of dust in mine too.
 
BAD SVT said:
thats true brian. i dont have any gasket @ that junction as well. neither do i know where i could get one. i'm sure there'll be a bit of dust in mine too.
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what is interesting is my SVT also has a KKM adaptor and I think it closed up fine ....
 
I do have a MAF adapter and that is actually something that came to mind at one point. I posted up on NECO asking if there was a gasket i could buy for it, but got no response on that part. I wonder if its something you could make out of a sheet of gasket paper?

I have tried unplugging my MAF but it makes the car undriveable. Usually if i try to unplug it when its hunting for idle i dont make it in time and it smooths out. If i do get a chance to go to the scrap yard i will pick one up and see what happens
 
Soi got a MAF and switched it in. I cleaned up the housing and painted it too while i was at it :cool:. Nothing seems to have changed. One thing i noticed was a lot of white residue on the walls of the MAF housing. It all came off with a wire brush and i used the air compressor to blow it out. Is this normal? Or is it a sign of something? I also grabbed the gasket that goes between the MAF housing and the air box off a contour at the scrap yard and installed that onto mine. But as a said no change really. I couldnt change out the TPS as the ones i have are for a 2.5, and those wont work because of the way the TB turns, correct? I have a 3L tps also, does anyone know if this will work?

Brian, I wanted to do some datalogging to send to Nautilus and see if my tune can be adjusted any. The only problem is i dont have a laptop. Is there any chance that sometime in the future you would be able to help me out with that? If not, no big deal.
 
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