So I cleaned my air filter (K&N) yesterday. I went out to the truck and removed it and took it inside to clean it. I had to get gas in the evening, about 6 hours later. So it was plenty of time to let it dry.

Anyway, I clean it and put the oil on it and reinstall it. When I took off to get gas everything was fine. It idled nicely and drove like it did before. I pulled into the gas station and it started idling really really rough, almost like it was going to die.

I filled up the tank and drove off, and it continued to idle rough. I parked at the store and adjusted the idle air screw. Still idling rough (only at a higher RPM) and it sounds like it's misfiring. I say it "sounds like" because I can't say for sure, as I don't know what a misfire sounds like.

It drives and sounds okay when driving, but idling is really rough.

I thought maybe oil got onto the MAF, so I removed that today and checked/cleaned it. Still the same issue. I even recleaned the air filter and addedd less oil. I though maybe the oil was too thick and it was choking it.

How does a truck go from sitting and running fine to driving and running rough? Nothing dramatic changed in my setup.

I should also add that it runs fine before it's warmed up. Once it's up to normal operating temperature, it starts acting this way. It also has new wires and plugs and rotor and distributor cap. This was all replaced 2 months ago during the head job.

 

I checked the spark plug cables and vacuum lines already and everything is hooked up fine.

One question, though: can that anti-stick silicone grease for spark plug cables interfere with the conductivity of electricity from the cable to the spark plug? I removed the cables a few weeks ago and it was all dreid up. and I've applied more since then since I was messing with the plugs to do the compression test.

 

BUMP

no one yet? I cleaned the MAF sensor as well last night when I cleaned the air filter. I just went out on my lunch and checked the cables and hoses. All the vacuum hoses are fine. spark plug cables and distributor cap is tight.

On a cold start it's fine, but after it warms up it craps out and idles like . any tips? could the air filter have done it in? i've never cleaned a K&N filter before, but I followed the directions and did it properly.

 

any chance you did something to the AFM plug when pulling the filter in and out, such as maybe a wire broke or maybe there's some corrosion on the terminals and moving the cover around loosened a connection?

 

Nope. I looked at that and even checked the wiring to make sure everything was connected. AFM seems fine.

I did disconnect it when I removed the MAF to clean that, but that was only AFTER the problem emerged.

 

another probably dumb question- are all the clamps tight on the intake duct?
have you inspected the rubber parts for any cracks?

 

yup. all of the clamps are tight. no air leaks at all. i prodded around the air system some more tonight and didn't find anything out of place. it all looks good.

 

I wonder if the filter doesn't have too much oil on it and the ecu / o2 haven't adapted to the restriction yet...
if you removed the filter after the engine warms up, I wonder if the misfire would subside... do you have access to a paper filter you could through in there?
or possibly disconnecting the battery for a few minutes to clear the ecu fuel trim.

 

I threw away all my paper filters.

However, last night it didn't misfire and idle rough. My truck has a self-healing feature

It didn't idle rough or misfire, and I didn't change anything. On my lunch break all I did was recheck hoses and jiggle a few wires. That's it.

 

well one way for certain to check for air leaks is spray some starter fluid around the hoses and the airbox meeting joints and see if the truck idles up. classic 2 stoke move to check crank seals but should work in this instance.

 

Arrg. So Its sort of fine now. It seems when it's cold, it runs good. When it warms a little, it runs like crap. After it has been driven for a while longer then initial warmup, it's good again.

 

anyone? anyone? could it be bad (watered down) gas?

the fact that it runs worse when it's medium-hot doesn't give any clues?

 

I added iso-heet to the tank and a few days later added some techron injector cleaner. If it was bad gas, it shouldn't be a problem now.

It's still idling really rough. It's about 50/50 now. Sometimes at the stoplights it will be rough, others it will be smooth, like it was before this started.

I removed the k&n filter and ran it for a while to see if it was suffocating the air intake. Didn't make a change. I adjusted the MAF air/fuel mixture, and it didn't help.

Any other ideas on what it could be?

 

Check the injector connectors.I've seen those back off!
Bigblock

 

I checked those when this first happened. I disconnected each and listened to the engine after each was removed. The connectors seem fine. Even when I jiggle and lightly tug the wires to ensure the connectors themselves are good it doesn't seem to affect the engine.

 

may have been a bad gas thing.
adding the 'heet' to the tank is likely gonna cause it to run a little rough for a while, at least through the next tank. for the record- isopropyl (rubbing) alcohol will do the same thing and is cheaper. water doesn't mix with gasoline, alcohol will mix with both water and gasoline. alcohol mixes with the water and then mixes with the gas, then carries the water into the engine along with the gas. that's the principle at least.

I'm gonna wait before offering anything else until we see how it goes over the next few days.

 

the iso-heet was basically isopropyl alcohol. All the alcohol I could find in the local stores had water mixed in (80%water, 20% alcohol) so I opted to just buy the injector cleaner and iso-heet in one shop. I could have kept looking for straight alcohol, but I would have spent more in gas shopping around than it was worth.

I'm about to fill up another tank, so I'll report my findings.

 

I filled up the tank tonight with the best gas around (shell v-power). There's aren't many good gas stations here, just the cheap no-name "u-pump" and western conveinence (which has gas about 25 cents cheaper than anywhere else)

I still see the same stumbling and stuttering at lights. It seems a little better, but that could just be my imagination.