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Discussion Starter #1
Has anyone had an issue with a rough idle for the first 10 seconds or so when starting? It seems to only happen at cold start - no issues when it is warmed up. I did notice the LIM is leaking - could there be something related to this? Or is there a throttle position sensor that could cause this? It has 99,000 on it - just replaced the fuel filter about 3000 mi ago. Thanks in advance for you help
 

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Discussion Starter #3
well - after having the plugs, wires, and intake cleaned it runs better but still has the erratic idle at startup - until you blip the throttle a couple of times. it almost stalled out on me the other day while crossing a highway. Whe the car is warmed up it runs fine - no hesitation or rough idle - just when it has been sitting a while or overnight. Fuel pump has a little humming noise - not screaming by any means. Where do I go from here? Could this be a throttle position sensor issue - or a fuel pressure regulator issue?
 

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update - on Sunday I took the MAF out and cleaned it up - the 3 sensors were quite dirty. I put it back together and tried starting it and there was no rough idle. Started it again Monday morning and no rough idle. Started it Monday afternoon and the rough idle was back. I went to AutoZone and picked up an IAC and changed that Monday night. After replacing the IAC i still had the rough idle at cold start up and the hissing sound near the air intake/drivers side headlight area. But once it is warm she runs like a top. Went and picked up a FPR last night (i could smell fuel in the vacuum line but it was not wet) but i was not able to get the flare nut off the FPR without taking the TB or the whole intake off - so i threw in the towel last night and brought it to the garage - they put the FPR on for me - not cheap of course - then when i just went to pick it up this afternoon it STILL had the rough idle and hissing noise by the air intake/drivers side headlight area.

I am baffled - i think i'm going to dig into the headlight fender area and see if i can find any vacuum hoses in there?

any other ideas?
 

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Im having this exact same problem, Its does this everyday for me. For the first ten seconds it idles like crazy, it almost shakes violently. Any ideas on what this can be.
 

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Discussion Starter #6
When I started it this morning and it was fine - maybe it is cleared up - although lately it seems to have been the worst in the afternoon after it has been sitting while i'm at work. The worst thing about it is I don't even get a code on my scanner. I will be bringing it back to the shop next week sometime - the manager said he would like to look further into it (for free) - he would like to have it for a day and hook up the scanner and try starting it throught the day.
 

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8th Gen Antagonist
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I guess the upside to wasting money by blindly throwing parts at the car is that someone will feel sorry for you and help do an actual diagnosis. There are no vacuum lines in the headlight area btw, just the airbox.
 

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Discussion Starter #8
Thanks - I guess since i'm wasting money by blindly maybe a new trunk latch or new rear floor mats might cure the problem?
 

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Im having this exact same problem, Its does this everyday for me. For the first ten seconds it idles like crazy, it almost shakes violently. Any ideas on what this can be.
I would be happy to look into this for you with your VIN. Please feel free to contact me via private message. Thank you in advance.

Tricia, GM Customer Service.
 

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HELP

I would be happy to look into this for you with your VIN. Please feel free to contact me via private message. Thank you in advance.

Tricia, GM Customer Service.
I am having the same problem! I get a check engine light too. Any thoughts. I cant sink a lot of $ into this so I would like to fix it myself. Just changed plugs and wires BTW
Jim
 

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Discussion Starter #11
mine ended up being the head gaskets. the air bubbling in overflow after the engine was shut off gave it away. hope to get at least another 110,000 out of it now :)
 

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Two things. When buying sensors, spend the extra money and get genuine OEM GM sensors. Not the cheap auto zone ones. Try taking off the throttle body and then take off the IAC and clean the hell out of the throttle body and all the port holes with carb cleaner and an acid brush. As a matter of fact I would get that old IAC motor and clean it also and re use it or go get another from the junk yard instead of the auto zone one. Richpin 06 has a how to video on you tube for doing this on the Saturn s series. Both are pretty much the same. Only difference is the Impala is more difficult to take off. The cleaning part is the same though.
 

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2003 3.8L Impala - intermittent rough idle

I have a similar problem with my 2003 Impala and the dealer cannot recreate the problem nor find anything wrong. It has 104,000 miles and normally runs very well with great gas mileage. About once every two months it will start with a very rough and slow idle with lots of chugging and spark knock noises much like the "dieseling" sound of 1970's cars when you turned the key off. However my problem is usually on a cold start (summer or winter) with the ignition key on.

Also there is an unusual roughness in every cranking startup sequence that is a bit like a weak battery doing some quick chugging, but usually the car starts and runs fine.

This all points to a severe spark advance during starter cranking and then sometimes continues during idle, but no trouble codes nor any dash warning lights are ever seen. What could advance the timing at starting all the time, and then intermittently keep it severely advanced at idle, and not throw any trouble codes?
 

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Back in Black
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Sticking IAC remove it and clean IAC and throtle body, see if that helps. Ref to post #12
 

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Mr. Handy
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Check the large vacuum connector going to the throttle body. The is prone to cracking and will cause idle issues and a hissing sound. That or the Fuel pressure regulator could be going bad.
 

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Yeah I've had this problem going on for a while now (2 years) but it rarely does it now, because I let the pump prime itself, turn the key to ACC for 1 sec then ON for 1 sec then start it, I've found that that trick makes it start easier and never has that missfireing issue.
 

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Mr. Handy
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Yeah I've had this problem going on for a while now (2 years) but it rarely does it now, because I let the pump prime itself, turn the key to ACC for 1 sec then ON for 1 sec then start it, I've found that that trick makes it start easier and never has that missfireing issue.
This is actually the correct way to start the vehicle. Turn to On and wait for pump to stop running then, click the key start and let go. Do not hold the key on start, it is not necessary and shouldn't be done this way.
 
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