Aftermarket Coil cause rough idle?

The Shape · Dec 2, 2003

I have been fixing up my GT for about 2 years now as most of you know from the multitude of questions I ask. Anyway it is in pretty good shape now nothing fancy just pretty much a stock daily driver. I still seem to have a rough idle though it doesn't surge just like if it idles for a long while it seems to buck and snort a bit. Most all senors are new as well as a new fuel filter and the plugs wires cap and rotor are all new. I did however buy an Accel high output coil when I first got the stang (before I came here and learned anything) Anyway question is could the coil cause the rough idle? My timing is at 12*, but I did replace the motor mounts with energy suspension so that might account for some of the roughness. Just wondering if the stock coil would make it smoother??????

The Shape · Dec 2, 2003

Mavrick · Dec 2, 2003

I would imagine the coil would help transfer spark through your wires.

For a rough idle, i'd recommend cleaning your IAB valve with a can of carb cleaner. It's fast, easy to do, and you can re-use the old gasket with no problems. This solved my rough idle problem, as well as many others.

The Shape · Dec 24, 2003

I'm gonna bump this. I have cleaned the IAC and the throttle body. The 02 sensors aren't a year old and the cap, rotor, plugs, and wires are new as well. It will idle ok in gear. In park it will idle fine a few minutes and then shake and buck a few seconds, and then smooth out then buck just not a very smooth idle. It also seems to be worse the colder it is outside. Maybe the car is just a bit cold natured and the energy suspension mounts magnify the vibrations I Feel?????? Any thoughts?

Nutty 5.o · Dec 24, 2003

I just had a similar instance on my 89. Put on some used headers and had similar effects. No loss of power/driveability, but a bit of bucking. Turns out a friend admitted to dropping a plug when reinstalling them. Found one gapped at .10. I guess when he dropped it, it closed the gap up. Spread it open to stock = .52-.56 and all good now.

Dave

The Shape · Dec 24, 2003

hmmmm that is something to check.

Mavrick · Dec 24, 2003

Clean your 10 pin connectors as well. There is a tech article around here that you can use as well.

The Shape · Dec 26, 2003

Ok cleaned the 10 pin connectors, and checked the plug gaps. I also cleaned the IAC and throttle body, and checked my TPS. Just wondering, but my power steering pump whines pretty bad. Could it be lugging the engine at idle since it is colder out and the fluid doesn't thin out as much as in summer?? The car doesn't surge it just idles kinda rough like it wants to stall it will be smooth then it will buck and shake the car and then settle back down a few seconds and the buck again and so on and so on. When driving it runs smooth no hesitation or missfiring, Just at idle in park. Doesn't really do it very much if I am in gear at a light.

Fox Saleen 163 · Dec 27, 2003

I doubt it's the power steering pump. But, to find out for sure toss a short belt on there that bypasses the power steering pump. See if that makes any difference.

Fox Saleen 163 · Dec 27, 2003

Also, I may have missed it while reading the thread... but have you replaced your fuel filter and pcv valve? Are your fuel injectors clean? I've had decent luck with the Marvel Mystery oil for cleaning and lubing the fuel system.

Your profile says it's an 87, is it still speed density?

The Shape · Dec 27, 2003

Yes still speed density. I replaced the fuel filter last monday and replaced the PVC valve along with the screen and the grommet the week before. I bought some castrol syntec fuel system cleaner last night and poured it in when I filled up I am gonna see if it helps any. I appreciate all of the advise so far.

jerry beach · Dec 27, 2003

Have you pulled the codes? I would do that first. Also try to isolate it to a cylinder if you can. Pull the wires off the dist one at a time, you must wait for it to shake and see if the shaking gets worse each time. I dont think it sounds like a coil prob. You could try cleaning the ACT sensor for the heck of it. Doesnt make any sense to me that its not doing the same thing in drive. So, dont let it idle in park, thats simple enough.

The Shape · Dec 27, 2003

Doesn't throw any codes. I did notice today it was warmer outside and it wasn't near as bad.

jerry beach · Dec 28, 2003

Beg, borrow or buy a fuel guage and make sure it is stable when the car is acting up. Could be you pump is starting to go out or the is getting low voltage at idle. Its got to be losing fuel or spark or getting too much air, right? I would also hook a vac gauge up to it when it is idling good. Just to make sure its pulling 18-21in hg, and steady. Just some simple things you can check out. Doesnt suprise me its not throwing codes.

The Shape · Dec 28, 2003

I really need to buy both a fuel pressure gauge and a vacuum gauge ( maybe as a belated christmas present to myself) Anyway I get in the car after coming out of a department store earlier this afternoon, and when I fired it up it idled a little rough as it has been doing and also this time when I put it in gear it hesitated a bit as i started to take off then cleared up and ran fine. So I took it out of town on some old highway backroads and beat on it a bit. It pulls strong as ever, and has no problems breaking the tires loose. So I don't really think it is an ignition problem. Not sure if a weak fuel pump would make it idle rough and still run good when you hammer it or not. I did notice after driving it good and hard for a few minutes it seemed to idle better. What should the idle RPM be on an AOD? I am wondering if turning the idle up a bit might help any?

jerry beach · Dec 28, 2003

I am not sure, but I think around 725 in gear would be close. Its hard to say without a shop tach stock ones arent known for accracy, and the puter sets the idle. That is a stop screw under the TB, not for idle setting. Mine is stumbling a little bit too at idle when the engine is cold. Has been doing it for over a year. It doesnt do it once it reaches temp., thats 160* for it and only 5min to get there. The stick cars are supposed to idle at 675 rpm, but few do. Mine goes 800-900, usually steady.

The Shape · Dec 28, 2003

Thanks for all of the help so far Jerry. I was thinking the computer was supposed to set the idle so I guess turning it up is out then. Any way went outside and popped the hood between my last post and this one and looked for any arcing of my plug wires they seem fine. But I did notice something I had forgotten all about. I have a small oil leak on the corner of my lower intake. It is such a tiny leak i haven't bothered with fixing it. Think a small leak like that could screw the vacuum up enough to cause my problems?

88stangmangt · Dec 28, 2003

sounds to me like sumething is dragging off your alternator makeing it work harder. Causeing your engine to run harder to keep from stalling and to supply the juice.And when you drive it is geting more than enough juice to supply it do you have under drive pullies? could be a bad power steering pump if it whines it might need more fluid or have bubbles or be bad. So i would drop the belt for a min or so run it at idle and watch. try this and let me know.

Good Luck!!

The Shape · Dec 28, 2003

Don't have underdrives , but the P/S pump does whine. Checked the level and it is full.

88stangmangt · Dec 28, 2003

my old p/s pump whined bad the internals do wear so drop the belt run it for a min (try it several times) and let me know then we can go from there.

Aftermarket Coil cause rough idle?

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