Possible bad spark plug wire?

[Jimmy9190]

I did a tune up on my Dakota yesterday. I used my existing wires, they are the Napa Belden Premium set and are only a couple years old. My plugs have metal heat shields on them and the wires have a long boot to reach down inside the heat shield. When I pulled the plug wires off a couple of my plugs, the wire boot was stuck on there pretty tight, even though I had used dielectric grease in the boots. I mean I had to yank on it hard to get it loose. I replaced the plugs with NGK copper core FRF-6's, used the better quality Napa cap and rotor, the Echlin brand with brass contacts.

Ever since I finished the tune up I have a very slight surge in the idle. It will idle at about 700 RPM, which is normal but every 10 seconds or so it will increase to about 800 RPM for a few seconds and then drop back down to 700 again. The odd thing is if I turn on the AC, the idle stays steady at 700 RPM.

I wonder if those 2 plug wires I had to pull so hard might have stretched the wires inside so now they don't make as good a connection? Can an engine still run OK or maybe run with a slight problem like a weird idle fluctuation with a couple plug wires that might be stretched like that?

I spent a long time looking and checking but I found no vacuum leaks, nothing knocked loose or anything like that. I have no trouble codes stored, CEL is not on. I have done probably half a dozen tune ups on my truck since I have owned it, never had this problem before. Truck ran perfectly fine before I did this tune up. It was not quite time for a tune up yet, I only did it because I had read online it is a good idea to do a tune up with new plugs after replacing a catalytic convertor, which I had done last week. Truck is running fine now, other than this odd idle problem.

I appreciate any help here. Sorry for the long post.

 

[Merkava_4]

How could you have stretched the wires if you pulled them by the boots?

 

[Jimmy9190]

Originally Posted By: Merkava_4
How could you have stretched the wires if you pulled them by the boots?


I grabbed them by the top edge of the boots, may have also had a good grip on the wire itself in the process, I have big hands and a strong grip. I know I sure had to yank the boot/wire hard to get them loose.

 

[Merkava_4]

Originally Posted By: Jimmy9190

I grabbed them by the top edge of the boots, may have also had a good grip on the wire itself in the process, I have big hands and a strong grip. I know I sure had to yank the boot/wire hard to get them loose.


I don't think you damaged any of the wires; you'd have a misfire code if you did.

 

[[email protected]]

Dirty throttle body? Maybe you knocked a vacuum line loose?

 

[Merkava_4]

It's probably either a dirty idle air control valve or a dirty throttle body.

 

[Rand]

if you damage the wires it will usually cause a misfire. not a slightly surging idle.

 

[Jimmy9190]

Thanks, it was just an idea, I have been reading a lot since yesterday. I also cleaned my throttle body yesterday and removed the IAC to clean it as well. I thought I might have pulled too hard on the IAC pintle, I was moving it around to work the TB cleaner down into the bore. I thought that might have been the problem so I replaced the IAC today after work. It seems better but it still has the slight surge in RPM at idle. I did not let it run very long in my driveway after I put in the new IAC. When it started surging again I just kind of got disgusted with it, shut the hood and went back in my house.

I am going to drive it tomorrow to work and home again, I am thinking the PCM may need more time to learn and calibrate the new IAC. If the idle surge is still present when I get back home I will try a new throttle position sensor. Truck runs OK, but has a bit of a dead spot at about 60 mph. I can gun the throttle and it has a bit of a delay and then the speed slowly begins to increase. I have spent a lot of time looking but can not find any vacuum leaks or disconnected hoses.

 

[actionstan]

Have you tried resetting the PCM? When I went from autolites to ngk(oem) plugs on my saturn I had a slight intermittent stumble for a while then it seemed to go away.

Also I could see the plug wires being damaged even when being pulled by the boot, I have had the metal piece inside of a spark plug rip out completely out when they were stuck on bad enough, but as others have mentioned a bad wire should cause a misfire.. I usually associate surges with vaccum leaks.

 

[david_ES2]

If it miss fires it will not always throw a code. A somewhat bad wire can cause a erractic idle like you explained, even though idle air valve is first to blame.

To see if its misfiring put a thin piece of card board or paper against the opening of the muffler, it should have a nice even pressure, if not its most likely your ignition system because thats what you touched and quite possibly that single wire you mentioned

 

[Scott_Tucker]

If it happened right after you had the issue with the wires, then it is most likely either the wires or something else you did while the wires were off. The chances of something coincidentally breaking is very low. Your PCM may not set a misfire code especially from that era, they weren't as powerful as they are these days.

 

[Charlie1935]

You probably messed up the IAC when you were moving the pintle around. Everything I have read on them says "Do not try to move the pintle or it will damage it".

 

[The_Jeff]

I would think a misfire would show up more under load. I've broken plug wires and known I've done it. Generally the little crimp connector stays on the nipple of the plug.

Try monkeying with the base idle screw. I know everyone says not to touch it, but I'm thinking that your ISC motor is confused between two possible positions: Too fast and too slow. If you bring the base idle up or down a hair this may help. Just remember how much you gorked it, 1/4 turn should do it.

 

[Jimmy9190]

Thanks for the help here. I drove it to work today, the idle problem is still there. It is cold for Florida today, probably 50 degrees when I left for work. The idle was OK at the first few red lights on the way here. About 10 miles into my commute when I stopped at a light the idle was rising and falling again, same as it did before I changed out the IAC last night. It was doing the same thing in the parking lot when I got to work. It is also still going to a steady 700 RPM if I turn on the AC.

There has to be a reason for this problem and I need to keep after it until I fix it. I used the exact same type of plugs as I had before, the only difference is I gapped the old ones at .044, these new ones I did at .040 which is the factory gap listed in my Dodge FSM. Last time I went by the gap spec on the NGK web page, which they recommended .044. I don't see how changing the gap could cause an idle problem.

I will try the tail pipe test (thanks David) and if need be I will change out my plug wires, I still have my old ones from the last time I did a tune up. They are also Belden Premium and should still be in good enough shape to test with.

I am still in the dark about the TPS. I have read that a bad TPS can cause an idle problem, but I do not know for sure if my TPS is the cause of this idle problem. I tested it with my volt meter, it is on the low end of the acceptable output voltage range, at WOT with the engine off I have about 3.6 volts. The high end of the spec range is 4.5 volts at WOT. I have looked and listened as much as possible and can not find any vacuum leaks, but that does not mean one does not exist. I just have to keep after this problem until I solve it. Truck was fine before I did the tune up on Monday so it has to be something I did.

Thanks very much for your help on this.

 

[The_Jeff]

A bad TPS can cause an idle issue because the computer is looking for "zero throttle" to know it should be in charge of idle control. If the TPS gives a flaky voltage it might think you're at "1% throttle" and let the idle fall where it may. Potentiometers do eventually wear out. When the computer is "not in charge" of the idle it may intervene under what it considers to be an emergency, causing the lope.

Your cold start smooth idle could be from the drag of the fan before its clutch warms up and loosens up, or from running richer/ faster.

 

[Mr_Incredible]

I had a real bad problem on my '89 CRX that wound up being a bad plug wire.

Was ok at idle but would cut out, pop and spit, and even backfire from 1900rpm to 2300rpm. I checked and changed everything I could find or think of. I specifically did NOT change plug wires because they were only a couple of thousand miles old.

However...I had removed the valve cover to lash the valves and damaged one of the wire to plug connections. I had thought everything felt outstandingly good removing and replaced the plugs and wires when I had done so. I was in error.

Once I found and replaced all the wires again there were absolutely zero problems.

 

[Jimmy9190]

Originally Posted By: eljefino
A bad TPS can cause an idle issue because the computer is looking for "zero throttle" to know it should be in charge of idle control. If the TPS gives a flaky voltage it might think you're at "1% throttle" and let the idle fall where it may. Potentiometers do eventually wear out. When the computer is "not in charge" of the idle it may intervene under what it considers to be an emergency, causing the lope.

Your cold start smooth idle could be from the drag of the fan before its clutch warms up and loosens up, or from running richer/ faster.



Thanks Elefino...I did two stupid things during my tune up on Monday. One was moving the IAC shaft back and forth too much and too agressively when I was cleaning it. The other stupid thing I did was I did not remove the TPS or MAP sensors from the TB when I sprayed it with TB cleaner. I wonder if some of the cleaner did not somehow get inside and ruin the TPS or MAP or both?

 

[Jimmy9190]

Originally Posted By: Mr_Incredible
I had a real bad problem on my '89 CRX that wound up being a bad plug wire.

Was ok at idle but would cut out, pop and spit, and even backfire from 1900rpm to 2300rpm. I checked and changed everything I could find or think of. I specifically did NOT change plug wires because they were only a couple of thousand miles old.

However...I had removed the valve cover to lash the valves and damaged one of the wire to plug connections. I had thought everything felt outstandingly good removing and replaced the plugs and wires when I had done so. I was in error.

Once I found and replaced all the wires again there were absolutely zero problems.



Thanks..I don't have any pop, sputtering, stumbling or any other problems. just this odd idle surge from normal 700 RPM to about 800 or a little higher. Judging by the gas gauge I am losing MPG as well. I don't think the plug wires are bad after reading here and Googling it. I think I have either have a vacuum leak or maybe a bad TPS.

 

[Jimmy9190]

I fund a Youtube video of a bad TPS..This is exactly what my truck is doing, only the idle is from 700 to 800, maybe 850. In the video it is surging from about 1000 to 1250..

http://www.youtube.com/watch?v=ULiXUX0sJVo

I hope/wonder if a new TPS will fix the problem. I tapped on my existing TPS with a small hammer, it made the RPM jump up. That may be normal though since a TPS is a potentiometer..

Any thoughts on this?

Thanks for the help here.

 

[Jimmy9190]

I picked up a new TPS after work at Auto Zone. I installed it a few minutes ago, it *appears* to have solved the problem. When I first put it on, I still had the fluctuation in RPM at idle. I let the truck run a few minutes, held the throttle at 1500 and 2000 RPM for a few seconds, let it off, it idled back down to 700 and is now idling steady at 700 RPM. I hope this is the final piece of the puzzle, that it really is fixed now. I have to drive it to work tomorrow to know for sure.

Thanks everyone for your help here. I hope I am done with this problem for good now.