2001 GC slightly rough idle

Hey guys,, van was idling rough and found out that a plug was cracked. Hado the plugs replaced about 4 months ago but due to the high charges the dealership wanted, did not replace the wires until tonight. The van still has a slightly rough idle. Engine will idle fine and then feel like it is getting pulled down and then back to smooth idle. Will do this over and over. Engine runs fine going down the road. No rough running. Oil is changed every 3K miles. I think it may still have the original battery (just bought the van a year ago) and do not know if the fuel filter has ever been changed. It has the 3.3L Flex engine. Any ideas??

Thanks

Rex

The list of possibilities is long. These may shorten that list.

If you think it's ignition related:
> Connect a timing light to each plug wire and watch for a steady uninterrupted flash. If you notice one is erratic check it's connection at the coil for corrosion. Make sure it connects tight. All is well? Test the coil. Here's how: http://www.autozone.com/az/cds/en_us/0900823d/80/1a/3a/74/0900823d801a3a74/repairInfoPages.htm If the coil is good make sure the PCM connection is clean and tight.

Fuel related?:
> Buy a mechanics stethoscope ($15), touch it to each fuel injector and listen for a steady click. Might be able to feel it. http://www.autozone.com/az/cds/en_us/0900823d/80/1a/42/38/0900823d801a4238/repairInfoPages.htm If one skips, make sure it's connection is clean and tight then measure it's resistance (around 12 ohms). If it's much off from that (compare to others) change the injector. You can connect an injector test light at each injector connector to verify steady voltage from the PCM.
> Connect a fuel pressure gauge at the fuel rail test port to verify steady pressure (50 psi).

Other stuff:
> Clean the throttle body (TB) and idle air control valve (IAC). http://www.autozone.com/az/cds/en_us/0900823d/80/1a/42/16/0900823d801a4216/repairInfoPages.htm How? Disconnect the main 3 inch diameter air duct from the TB. You'll see the throttle plate in the TB. Spray the area with a TB cleaner. Also spray the small opening for the IAC valve port.
> Pour a can or two of fuel system cleaner the next couple times you fill up.
> Gonna be a small one but look for a vacuum leak. Inspect all the vacuum tubing under the hood for cracks. With the engine idling spray the base of the intake manifold with brake cleaner. If you hear the idle change, you need an intake manifold gasket. The liquid temporarily blocks the leak and returns normal vacuum pressure.
> Normally I'd say do it but, in your case I'll say it wouldn't hurt to get a load test on the battery. Long shot but, there is a slight chance it could be effecting this.
> See a service engine soon light?

> PCM = Powertrain Control Module located next to the battery on the fenderwall.
> These links are for a 99 but your's should be simular. Recommend you buy a maintenance manual ($15/20) or subscribe to a manual at Alldata.com ($15) if you're planning on getting up to your eyeballs in this. Keep in touch.

I was just getting ready to post but this thread seems simular. I got an 01 as well. I have been getting this miss every now and then. Gets alot worse after the car washes, maybe every 5 seconds it just seems to send the spark somewhere else but the plug. Only happens in gear and more with the AC on. I just spent about 7 hundred on a tune up and injector cleaning. Plugs and wires are new, maybe about 3 months old. I figured I'd get a spray bottle and spray around with the engine running in drive resting against the house. I started spraying the front plug wires where they meet the plugs and I could see spark on 2 of them, same at the coil. Same miss I have been feeling for some time now. They all seem tight when up plugging. I put a good amount of elec. grease in them and seemed to help at the plug side but I can still see spark at the coil side. At first the spark was coming through the boot, with grease it seems to come out the bottom part of the boot where it meets the terminal. What should I do RIP? RIP them out and go to dealer and RIP their heads off? Lol. Sorry, couldn't resist...so what should I do, or what can I do? Thanks

Cntrysthbst - Sheesh. You highjacked the thread. Well at least it's the same subject.

IMHO not sure that spraying down the plugs (water I assume) is the best way to troubleshoot this. You may be inducing another problem and covering "the" problem. I would think the amount of water that could possibly get into the engine compartment during a car wash would fall far below what you are spraying. Plus I would think you could spray just about any engine with a spray bottle and see the same result. I can't say for sure. Just a theory.
During a wash, unless you're spraying gobbs of water though the grill, the only other path could be past a bad engine compartment seal. With the hood open you might try pouring water down the windshield and watching for it to get by the aft compartment seal on the cowl. It might be leaking past it and onto the rear plugs.
Then there's the humidity factor. When you wash the car even if the seals are solid, humidity can be a factor. I would think that would especially apply if your plugs/wires were one step from the circular file. Your's are new. Even better, yours are OEM from the dealer. That said, humidity can effect any electrical connection. How many are there on this van?

I'm not answering your question, "What should I do". Since you implied it happens elsewhere besides after a wash, I would do as I suggested in the above post. Connect a timing light to each wire and make sure you see a constant flash on each. If you see a break in the flashes, you know which is the problem. Troubleshoot backwards to the coil and PCM. I don't recommend it but, if you want to shotgun parts, the coil would be a good bet (can't keep up with the demand under load - in gear & A/C on). Keep the PCM out of the picture for now. Beyond that, everything in the above post applies, especially that first sentence.

This book may get edited.

Yeah that's a good point about the water not getting up to the plugs in a wash....don't know what I was thinking....will check those other places. This slightly rough idle, in gear of course, is causing the gray to start showing more. Ok, off to buy a timing light. And thanks for that info, very helpful, it will keep me busy for a week.....

Thanks RIP..All sound like things I should be able to handle pretty easily. Guy at AutoZone told my wife that if we didn't replace the plug wires when we had the plugs replaced, then the new plugs could have fouled (one of the old plugs was cracked). I'm no professional mechanic but it made sense to me. Thoughts? Also, if anybody cares, it is very easy to get to the back side plugs by removing the wiper blades and basin with the wiper motor. If I had known that when I had the plugs done I would have done them myself :banghead: . Will try to get to RIP's suggestions this weekend and post results.

OK, so wife calls me today and says the CEL is blinking for about 10 seconds and goes off. Calls back later and says that the engine is running even rougher. Got it to the barn wouldn't you know it, another cracked spark plug in #2 cylinder. Replaced plug and purrs like a kitten. Now, what are the chances of having 2 cracked spark plugs back to back? Don't know if they were from the same cylinder but after seeing the old wires, I am betting they are.

Another plug cracked? We breezed right by that one didn't we. Who woulda thought? Anyway, yes it's a good idea to change the plug wires, especially with another cracked plug. Something was going on. Sounds like it was the problem all along. If you want and you still have them, try checking the old plug wire resistances with an ohmmeter. Longest should be around 18K ohms, shortest around 10K ohms. The others will vary between those by their length. I'd bet one is out to lunch.