I developed a rough idle condition after working on the head of my truck. I got everything back together last night. It idled fine in park. Then when I put it in drive it kinda felt like it was starting to idle rough. The entire way home while under gas it was fine, but at stops it idled rough. RPM's dropped to 500. While in park it's up around 600-700. Today it's the same thing. I disconnected the battery and tried to relearn the program. It's the same thing.

Any suggestions?

 

Same here, it must be the Wedgewood blue ones.......

Did you notice it after you put on your exhaust? now try this, run the motor up to 1700-2000 RPM, in park.

Post what it does here after you try it.

 

JStang,

Nothing unusual happens at 1700-2000 rpm's. No vibration, no pop in the exhaust.

I checked my connections and vacuum hoses and they all look good.

 

What did you do to the heads?

 

I had to fix the passenger side. I had the infamous plug launch. No port or polish work (i wish!)

It's almost like the truck needs to idle like 50 rpm's more. It goes away while in park or neutral.

 

Your lucky, mine shakes like crazy at 1700. I've had it to the dealer many times, they tell me its due to a lean mixture. By putting on the exhaust it has been leaned out even more. I did notice the idle drop as soon as the muffler was put on. I think a drop in back pressure has something to do with it.

 

JStang,

No problems after the exhaust. I did the exhaust years ago though. I think I had the truck about 2 months or less when I did that. That was almost 4 years ago!

I was thinking in what it possibly could be and I am coming up with zero. I will check the plugs tonight before I leave for some snowmobiling this weekend. I replaced the fuel filter less than a month ago. Could it be the throttle body? I didn't really clean it when I had it off last weekend. I had gunk on it, but I figured, why mess with it if it's working. (I only need one problem at a time!)

 

Out of curiousity, check to make sure the plug wires are on the right coil number. This should trigger a CEL, but you never know.


Mike

 

I'll check the wires. I know they are all on. I did the driver's side and my cousin did the passenger side. I will check tonight.

It is amazing what does and doesn't trip the CEL. Blew the plug out, no CEL. Leave the gas cap loose, get the CEL.

 

Mine also vibrates at idle while in gear. If you put it in park or neutral, the vibration goes away. The vibration feels like a four cylinder engine at idle. Not very rough, just not right for an eight.

 

I think I may swap out my plugs this weekend. I have the +4's but I may go back to original equipment. 7 of the 8 have about 60,000 on them. Then I will make sure all of the wires are still right and I have lot's of di-electric grease in there. To me it does feel like a vaccuum line is off. The wierd thing is that when I took off the head, I found a line that had been melted apart. Both ends looked seal. I cut the ends and put a peice of vacuum hose in it's place. I thought that this would work. I can't remember which line it is. I remember it was red.

 

Mine idles low and rough in warm to cool weather with the a/c off. It will drop down to close to 500 rpms and sputter like it's going to die. It might not be something you did, my truck has never had the heads off. It has had the timing cover removed for a leak repair though? It clears up when I clean the IAC, or run Redline Fuel System cleaner through it. Then a few months later it comes back. Try replacing the IAC, or cleaning it out. You might be pleasantly surprised?,,,,98

 

Ahhh, I have heard the same thing about the +4's several times. I would try that also, definitely!,,,98

 

I had a 95 GrandCherokee that did this too. It would idle fine in park or neutral, but put it in gear under a little load and it had a slight miss/rough idle. It started about 5k miles after i changed the plugs to Bosh Platinum. I then had a f-150 come in to work with the same problem and I determend it had slight miss on one cyl. Pulled the plugs, Bosh platinum. The guy was pissed when we told him he needed new plugs, he just had these put in abot 3k miles ago. Put in new motrcraft and problem solved. So I changed them in my Jeep, problem solved. In the 2 years i worked as a tech I personally had to change Bosh plugs 2 times for a rough idle/miss in 4.6 f-150 trucks plus my own vehicle. I am not saying for sure it is your problem, but it may be a good place to start with plugs/wires(if applicable).

 

my idle dropped too after i had my exhaust put on but it runs smooth at all rpm's.