Engine stuttering, RPM jumps, bad idle...

[Earnhardt132000]

Just got my car out of winter storage and am having some problems. It first started when I was leaving my parents house when I just put the plates on it. It was stuttering and had a lot of hesitation when accelerating, but that went away after driving it for a half hour. I figured it was bad gas or something... Then it started acting up again a few days ago. The engine will stutter and hesitate under acceleration, and idle is rough. You can hear put-put coming out of the exhaust every now and then, so I'm guessing its a misfire? I'm getting no code, so I can't narrow it down. The car has a 3.8L with 212k on it. My dad said we could try changing plugs and wires, but I'm not sure if thats the case. I was on my way home from school today and I noticed the RPMs have started to jump as well (at least on the tach), this makes me think its a sensor. Possibly CPS? I had this happen on my winter car, seems like similar symptoms. Any input?

[Choppers]

Re: Engine stuttering, RPM jumps, bad idle...

Might be bad gas. Try changing the fuel filter. They are cheap.

[Bandit127]

Re: Engine stuttering, RPM jumps, bad idle...

Fuel filter change and some seafoam in the tank.

My engine is doing the exact same thing, and it goes away (99%) with a warm engine.
Heres my theory:

Injectors sat all winter, get gummed up and this causes weird RPM's and bad idle and hesitation. Once the injectors are warmed up, they clear up a bit. Injector temps do effect how they operate btw!

My injectors, sat for no clue how many years, and I've put 55 miles on this engine so far, and with half a can of seafoam in a half tank of gas. It idles alot better and RPM's are smoothing out. Still have a hesitation but that too is showing improvement.

So, if you throw in a can of seafoam into the tank and run it for awhile after changing fuel filter it should clear up. Otherwise, it could wires/plugs or your injectors need a deep clean from a shop injector cleaner.

[3.4orNothing]

Re: Engine stuttering, RPM jumps, bad idle...

be happy...its not your opti spark...............but it does sound like a misfire.....a friends car did the same.......oil leaked on the plugs while it was stored..

[Earnhardt132000]

Re: Engine stuttering, RPM jumps, bad idle...

Finally got a code that showed random misfire, so I left it with my dad and he changed the plugs and wires. Has been fine for a couple of days, now its doing it again. What can I try next... coil pack?

[Bandit127]

Re: Engine stuttering, RPM jumps, bad idle...

A coil pack will have an entirely different symptom. They either work, or they are dead. Zero 'inbetweens' unless if you have a none-OEM one, in which I have had a few funky issues.

Check your fuel pressure with the ignition on, then with the engine running. The PSI should drop only a few pounds at idle.

Then you need to do a volume test, in which it should fill a 20 ounce bottle halfway in 10 seconds with the engine on. Or 1 fluid ounce per second.
The key to that test is grabbing a fuel pressure gauge with a relief valve and tube. The one I use is a Snap-On but theres no reason to be paying triple digit dollars for a once or twice use. See if you can rent one that has these features.

The last fuel test is to start the engine, turn it off and check the PSI, and make sure it holds that PSI for 5 minutes at least. The system will eventually bleed its pressure, but not that fast. If it does, look for a fuel leak.

The first basic tests are spark, fuel, and air. You covered spark, air is a given, lets make sure we aren't fighting a fuel issue.

You did change the fuel filter right?

[ssms5411]

Re: Engine stuttering, RPM jumps, bad idle...

I would check your injectors might have 1 clogged or starting to die out, you can check the omhs on them but it still can be bad even if the ohms are 12-18 ohms, if you have hptuners I think you can look at each cyl. to see which one is having the most misfires. I know on my Aeroforce scanne gauge I can view each cyl. misfire which is great. I had a bad injector once and couldn't find it for about a year, replaced wires,coils, plugs, maf, and map sensor only to find out a injector that still had good ohm out put but wasn't spraying all the time when it should have. Found it out after the engine was rebuilt and they put that injector in the #1 cyl. and the car wouldn't start, so 1 injector later the car ran like a champ and ever since then. Granted it stull could be other things loose wires or something but good luck finding it.

[Earnhardt132000]

Re: Engine stuttering, RPM jumps, bad idle...

Finally got a cylinder 3 misfire code, but I'm not sure which coil number 3 goes to. I want to check to see if the wire is getting burnt anywhere, and want to see how the connection looks. Anyone have the layout that the coil packs send to? Mine are all aftermarket since the motor has 212k on it... I am also thinking of running injector cleaner, any specific one to look at?

[Bandit127]

Re: Engine stuttering, RPM jumps, bad idle...

From experience, anything you can buy at an auto store is a complete waste of time, all they do, if they do anything, is treat the gas, and is more preventative than corrective. They 'might' clean a dirty inj, but not a clogged one.

What you need to do is take it to a qualified shop with a heavy duty injector cleaner. Because if its a clogged injector, you'll need to have it heavily serviced.

Any chiltons or hanes manual will have your firing order and coil pack association listed and pictured.

[Mogobs30th]

Re: Engine stuttering, RPM jumps, bad idle...

Finally got a cylinder 3 misfire code, but I'm not sure which coil number 3 goes to. I want to check to see if the wire is getting burnt anywhere, and want to see how the connection looks. Anyone have the layout that the coil packs send to? Mine are all aftermarket since the motor has 212k on it... I am also thinking of running injector cleaner, any specific one to look at?

Trace the no. 3 plug wire back to the coil. But Im doubting its your coil. From what I have experienced, if the the coil is bad, it will affect two cylinders (the two it operates). If its a specific misfire of a certain cylinder, my guess would be a plug, arcing or damaged wire, maybe an injector thats clogged or getting a bad signal. Its not outside the realm of possibility that its a coil, but its a little harder to have a bad coil and only one misfiring cylinder. As it was said earlier, either the coil works, or it doesn't.

I think once you narrow it down by eliminating the plug and wire, then I would start leaning to more complicated issues.

[Damascus]

Re: Engine stuttering, RPM jumps, bad idle...

I'm not sure if this will clean up a severely clogged injector, but I've always had good luck using Lucas' upper cylinder lubricant/fuel injector cleaner. I try to use it every 2 tanks of fuel on my cars, even though my recently aquired 96' Camaro only has 63K on it (only 5K put on by me), my little eco-car, a 96' Toyota Tercel 1.5L has 260K on it, 200 driven by me, and never has had any fuel system trouble (knock on wood), perhaps due to Lucas UCL/FIC.

If you completely rule-out fuel injector malfunction, I would try replacing the coil pack that controls cyl.#3. Or perhaps upgrade the set with MSD ones? Have you changed the fuel filter yet? Tested your fuel pump? Good luck!

[Earnhardt132000]

Re: Engine stuttering, RPM jumps, bad idle...

Ok, so on my way to school this morning it only did it once, until I pulled in my parking spot and then I could hear it misfiring while idling. I'm not sure if that means it is heat related, since my car has just enough time to warm up as I pull into the parking lot. I have not changed my fuel filter yet, don't have a jack at my house. I'm not sure how to test my fuel pump, I have a lot of posts here but not so mechanically inclined. Nor do I have any tools at my house, my dad has all the tools. I'll give injector cleaner a try, probably won't hurt. Maybe I'll pick up a fuel filter just to get it out of the way...

[Earnhardt132000]

Re: Engine stuttering, RPM jumps, bad idle...

Alright so I've been reading a little more into this, but still not solid on anything. However, I have come to the conclusion that I only notice the rough idle after the motor has warmed up. I am driving out to my parents house after class today, which is a 45 minute drive, and I'm going to check to see if the cat is glowing red to see if it is clogged. Yesterday I checked the connections on the coils to see if there was any corrosion and didn't see any. I added some of that Lucas upper cylinde and fuel injector cleaner but haven't noticed much difference. I plan on changing my fuel filter soon, whenever I can get a jack or lift. Alright I guess I should pay attention in class...

[Blizzard242]

Re: Engine stuttering, RPM jumps, bad idle...

Unless I'm completely fabricating this there are a few members on the board that have had intermittent troubles from coil packs so I don't think you should entirely rule those out yet. Anyways, I believe you can have them tested at an auto store which shouldn't cost you anything unless they're bad.

Also, i'm not sure if anyone else has mentioned it or not but the IAC (Idle Air Control) valve is a cheap and easy replacement that you may want to look into.