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Sometimes a very rough idle

6K views 15 replies 6 participants last post by  Hankster 
#1 ·
Like the title says, sometimes my van has a very rough idle sitting at a stoplight. Sometimes I will stop and it seems like it is going to stall and other times I come to a stop and it will idle great then slowly start to idle rough. When it seems like it is going to stall, if you let go of the brake and let the engine pull you forward without hitting the gas, its like the engine is chugging. It doesn't pull you forward smoothly. All my other cars I have driven if you let go of the brake, the car will pull you forward smoothly. I have a guess maybe why this is happening and hopefully one of you guys can tell me if I am full of it. One of my lifters is very nosey. I am thinking maybe at idle the lifter is not lifting all the way and then the valve does not open all the way, hence the intake/exhaust can't get in or out of the cylinder. Does that sound reasonable or bs. The spark plugs and wires have only 5,000 miles on them and replace with the right ones. Also when I changed the egr valve out to get rid of the check engine light, it did not change anything but it did get rid of the check engine light. What do you guys think?
 
#3 ·
Well which one, after I fixed the warped heads and got it running after three years, there was six check engine codes. A few I remember were egr vavle, injector #6 not working, radiator fans not working and a few others. All the codes have been fixed by me or a mechanic.
 
#4 ·
If there is no check engine light and you want to investigate the lifter, the best test would be a compression check. If the valve were not opening at low rpm, a compression tester would show lower on the problem cylinder.
 
#5 ·
if you have not done so already, try a different brand / grade of gasoline before pulling things apart.. injector cleaner might be good to try too if the van sat for 3years without being started - there could be crud floating around in the fuel system..

also (from personal experience) modern fuel blends tend to become "funky" if they sit for more than a month of two (some lose their octane rating even faster)
 
#9 ·
Thanks but we tried. We put different brands and grades. When we had the van in to get a new pcm( to get injector#6 working) they put a fuel system cleaner in there too because we drove around for 4000 miles on 5 injectors.
 
#6 ·
I had that problem with my recently purchased 2002 T&C with 105K on it. I put in a bottle of Lucas fuel system cleaner and a bottle of prestone 0-60 octane boost into a full tank of gas and let it sit and marinate over night.

I haven't had the chug or bogging sensation since.
 
#7 ·
:Wow1:I will have to remember that concoction.:lol:
 
#11 ·
as we get more info it starts to look more and more ugly..

I'd say if the rough idle is not constant / consistent (happens "sometimes" under same conditions) you can hope for nothing major.. otherwise it doesn't sound good

I'd see if a mechanic with a DRBIII or equivalent can verify correct PCM operation & check (maybe yourself) for vacuum leaks, air filter blockage, egr is operational and throttle body is reasonable clean...
 
#13 ·
The egr valve is new(still could be defective although it is no longer throwing a check engine light) and the throttle body is clean. I will have to get my buddy to bring the van to a mechanic to hopefully run a few tests on the pcm. Maybe he might be able to figure it out.
 
#14 ·
OK sorry for the long delay(working 60 hours a week puts a few thinks on hold) ,but today I got around to doing cylinder 2,4,6(the front three). Cyl 2 was 155psi, cyl 4 was 105psi, and cyl 6 was 165psi. I dont hear the noise from the back so I didn't tear things apart to get to the back three spark plugs. Seems like there might be something wrong with cyl 4.
 
#16 ·
It could be a sluggish ais motor its on the throttle body and regulates the idle speed.
 
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