rough running problem unknown

[vermiltina]

well my mate has a fairlane that seems to have a miss, its duel fuel.
when idleing it vibrates heaps like its a big miss!!! its got new plugs and leads and have tested all the coils and are all good!! it runs the same when on petrol and gas..
yet when you are at about 80 to 100 it runs as smooth as, as if there is no problem at all

burnt valve?? bent push rod??
just don't know, does anyone have any ideas??

[ratter]

Check for vacuum leaks, they are normally worse at lower revs.
When the plugs were out was a compression test carried?

[Blue_Flame]

My AU11 Fairlane with the VCT 6 does this, idles like **** but smoooooooooooth everywhere else.
Goes like a hairy dog and gets great economy out on the H'way
I have been chasing this problem near on six months.
Things I have tried/replaced include, plugs, leads, oxygen sensor, TPS, idle speed controller, fuel filter, air cleaner, PCV, I have cleanded the injectors and throttle body along with the fuel pressure regulator.
I have also checked and tightened the inlet manifold, a couple of loose bolts were found and I have eliminated the chance of a vacuum leak.
After all that, it has not made one iota of difference, I feel cheated, I thought that after each change something would have made a difference.
After some research, I like to put the idea out there of a broken/dodgy cam chain tensioner allowing things to a get little out of sync at idle but when the engine starts driving it all runs in harmony again.
The other anomaly leading to this conclusion is, in park, if I give the motor a blip on the accelerator, it does not return to idle straight away but will drop first to about 1500rpm for about 5 sec's then return to about 800rpm.
I know there are some mechanics out there, what are your experiences with this problem?

[JK EX CHASER]

Reset ECU with all electrical loads on.

[XRGhia]

try replacing the coil pack anyway... the one on my AU tested fine but then swapped it with the one from the EF, the EF started to run wierd (due to a dodgy coil pack) and the AU was fine... the AU was an au1 btw so bought a new one, runs fine and better on gas now

edit: i did also try new gaskets, intake bits all the way down to the smallest bolt and it didnt make a difference.... changed the coilpack, it ran fine (as described above)

[Blue_Flame]

Originally Posted by xrghiawagon

try replacing the coil pack anyway... the one on my AU tested fine but then swapped it with the one from the EF, the EF started to run wierd

Define running weird, poor idle or missing under load.
Just curious as to your symptoms.
Cheers.

[XRGhia]

running wierd = when i swapped the EF's coil pac into the AU, it ran fine right throughout the rev range so i put the AU's coilpack into the EF and then the EF ran like ****... So I got a good and working replacement coil pack for the AU and now its running beautifully.

The AU's coilpack was causing the AU to run/idle like a dog, hardly wanted to move away from the lights, as the revs went up, the engine was shaking more and more until 3500rpm when it was mostly disappeared. It felt like the bottom end was stuffed but gave it one last chance with the EF's coilpack... and it ran.. it ran like new..

To this day (this only happened 3 weeks ago) its running perfectly both on petrol and gas

[Beer Baron]

Grab a can of ya girlfriends favourite deodorant and spray around all the gaskets after the throttle body. It will smooth out if there is a leak as it will be burning the deodorant.

[Mr Hardware]

Plus your engine will smell like it just had sex

[saber]

Originally Posted by Beer Baron

Grab a can of ya girlfriends favourite deodorant and spray around all the gaskets after the throttle body. It will smooth out if there is a leak as it will be burning the deodorant.

So funny, yet so effective! Great for finding any vacuum leaks. You'll instantly notice a change in the engine when the deodarant is ingested by the engine.

Plus you'll smell like roses at the end of the job!

[Fordman]

Possibly inlet manifold gasket, my ba had same symptoms and it was this.

[Blue_Flame]

Originally Posted by JK EX CHASER

Reset ECU with all electrical loads on.

Done this a couple of times, once after cleaning injectors and again after replacing the O2 sensor.
Each occasion made no difference.

[vermiltina]

we are thinking it might be the harmonic balancer so we will soon see