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K-Dawg
09-27-2008, 11:53 AM
My car has been stumbling at idle for a while now. Almost feels like a vacuum leak. I changed the coil out a few weeks ago and it immediatly stopped hesitating. About 2 weeks later it started to do it again and it has gotten progressively worse over the last week. Probably the worst it has been. Is it possible that the coil is already shot again? Or is it that maybe it was a small fix for a bigger electrical problem (Opti :()? It almost felt like it was going to die on me last night. I had to push the gas in while holding the brake at a stop light and it was still stumbling a little.

What's my problem? I'm thinking about doing an entire tune up. Replacing the coil (again), opti, plugs, and wires. I just wanted to get some fellow LT1'rs thoughts before I jump $500-600 into replacing all that.

Thanks in advance.

Tyler Wheat
09-27-2008, 02:45 PM
Sounds like an opti issue, but then again, what doesn't?

A couple of questions:

SES light on?
Is this a random cylinder misfire or do you know that its been one or two of the same cylinders crapping out?
Does the miss go away with RPM or is it continuous through the entire RPM band?

If the SES light is on, go get it scanned and see what turns up. DTC 16 is low resolution pulse which is definately going to require replacing the opti. I think there is another one that's opti related. DTC 26 maybe. I really can't remember. Also, the SES light will usually flash under random cylinder misfire, but not always. If its not flashing, you'll have to figure out how many cylinders are dead and which ones. If you have headers, its real easy to figure out which cylinders are misfiring. Get a straw in a cup of water and hold your finger over the top of the straw (as to keep the water in the straw) and release to let the water on whatever primary tube for the desired cylinder. Makes it very easy to see what cylinders are dead. It wouldn't be that easy with manifolds, though. You'd be left shooting in the dark.

You can also check for any arcing under the hood from the wires. Just start it up in the dark, listen and look for stray spark.

Something else- have you replaced the ICM? That could be something worth looking at. I'm not sure if there is a way to test them, though. It would be alot easier and cheaper than the opti swap.

Another thought is you could check for vaccuum leaks. Just spray some carb cleaner on the vaccuum lines around the intake. See if that either helps or hurts the idle quality. If everything is in check, nothing different should happen.

I'm kind of leaning towards the opti on this one. The good thing is, its not going to hurt anything to do the whole tune-up if you have the money, not to mention its less of a headache to just do it all in one night and get it out of the way. If its actually due for a tune-up, you really won't be wasting any money. Just a little preventative maintenance. Like I said, there's no better time to do this than when the car is already torn apart if you end up needing to do an opti swap. Be sure to check the opti harness and clean any corrosion/gunk as needed while you're there, too.

Tyler Wheat
09-27-2008, 02:48 PM
Oh, and to make sure that its a spark problem, duplicate the problem and grab an extra plug you have laying around. Pull the plug wires off one by one and put them on the spare plug. Ground out the spare plug to something, start the car and make sure you have good spark. That will surely point you in the right direction.

fuels94
09-27-2008, 11:39 PM
Another item to check is TPS Trottle Postion Sensor

K-Dawg
09-29-2008, 09:57 AM
Sounds like an opti issue, but then again, what doesn't?

A couple of questions:

SES light on?
Is this a random cylinder misfire or do you know that its been one or two of the same cylinders crapping out?
Does the miss go away with RPM or is it continuous through the entire RPM band?


The SES light isn't on. I had autozone check it anyway and their was nothing. The miss does go away at higher RPM's. It hesitates at idle then stumbles a little as I'm accelerating, but normal driving speeds it seems to be just fine. I didn't have a chance to get under the hood this weekend, so hopefully next weekend I can look at a few of the things you mentioned.

Thanks for the info.

1badz
09-29-2008, 10:13 AM
Check fuel pressure before replacing anything

K-Dawg
10-13-2008, 02:33 PM
Update: I changed the plugs last night using ACDelco plugs. They were all gapped at 0.050. Today my car runs worse than it did before. It is really running rough at idle and is now running rough at all rpms. I made sure all the plug wires snapped back on so I knwo they are all tight. Also, the SES light came on today and it's reading a random/misfire. P0300 if I remember correctly. I also heard some clicking last night which kinda sounded like arching, but I couldn't see any flashes. Does this mean I got bad plugs or did I damage the 122,000 mile wires while I was in there? I'm planning on changing the wires anyway, which leads me to my next question. Which brand to go with? MSD? Taylor? Any AZ brand?

I also noticed there was oil on the business end of the plugs? Is that bad? I don't seem to be burning oil. Never see any smoke clouds behind me.

Thanks in advance.

IronOutlaw
10-13-2008, 03:29 PM
i think you need to close the gap to .040. thats what i run. try changing the wires. they are very easy to burn especially if you have headers. i run 25 dollar o reilly wires and havent had any problems with them.

Out of the aftermarket brands i like msd though.

K-Dawg
10-13-2008, 04:21 PM
i think you need to close the gap to .040. thats what i run. try changing the wires. they are very easy to burn especially if you have headers. i run 25 dollar o reilly wires and havent had any problems with them.

Out of the aftermarket brands i like msd though.
0.040? Really? These were pregapped and I checked the repair manual and it said to gap to 0.050. That's why I left them. I should have checked on here before replacing them I guess. I don't have headers either. One day maybe.

IronOutlaw
10-13-2008, 04:32 PM
I was told by my mechanic to run them .040, it gives you hotter spark. But really that shouldnt be your problem. Im leaning towards wires more than anything but they are a pain in the ass to do. Just two of mine got burned a couple months ago and they caused a huge difference in the way in run, and you couldnt even tell they were burned by looking at them.

landstuhltaylor
10-13-2008, 07:18 PM
Just one bad wire can cause a multiple cylinder misfire. The PCM will be thrown off by the one bad cylinder and try to compensate, instead it will just cause more misfiring. I found that one out firsthand.

hempkat94z
10-13-2008, 10:18 PM
Just one bad wire can cause a multiple cylinder misfire. The PCM will be thrown off by the one bad cylinder and try to compensate, instead it will just cause more misfiring. I found that one out firsthand.
I agree just had that same problem about a month ago. I bought Jegs 8.5mm wires and put them on the car and I am very pleased with them. They run ya about 40 bucks. here is the link about mid way down on the page.
http://www.jegs.com/p/JEGS/1064786/10002/-1

K-Dawg
10-14-2008, 05:02 PM
I kinda need something in hand by tomorrow so any of the high end stuff is out as they would all need to be ordered/shipped. I got a set of Belden from NAPA which they said are pretty damn good. Only problem, I noticed when I got home that they are only 7 mm. I called and the guy behind the counter said that wasn't a problem but I thought I'd ask here too. Is it okay to run 7 mm wires?

hempkat94z
10-14-2008, 09:05 PM
There are not a performance wire by any means but to just see if they fix the problem they should do the trick. I would still order some in the near future. Someone correct me if i'm wrong but don't they come stock with 7mm or are they 8mm?