Rough Idle

JMO · 05-05-2008, 08:10 PM

Hey guys,

I know there are a million threads like this one but I think my case is a little different.

Basically, the car has a pulsating roughness at idle (while in drive), but when in neutral or driving along, it's smooth as. There was what felt and sounded like misfire/pinging today as I started it but this only happened the once and hasn't happened again today.

I've cleaned the TB and ISC so can hopefully rule that out. The other things that I haven't checked as of yet are the sparks and leads (which would be lucky to have done 15000 km), o2 sensor and fuel filter.

Judging by what I've said, what do you think would be the most likely culprit?

Thanks for your help.

**Stav** · 05-05-2008, 09:19 PM

Air fuel ratios.Is it starving for fuel? Is it running too rich? The spark plugs tell you alot of what is happening in your engine .Pull out a plug.Take a photo and post it up.It may hold the answer.

JMO · 05-05-2008, 10:57 PM

If I had to say, I'd say it is running rich. There is a petrol smell to the exhaust and sort of a paint smell coming from the engine bay. I might have an over sensitive nose though :P

Is the o2 sensor the only part that takes care of air/fuel ratios or are there more parts to it that may need to be looked at/replaced?

I'll pull out one of the sparks when I get a chance and put up a pic.

JMO · 06-05-2008, 12:52 PM

I just bought an o2 sensor. It should arrive in the next couple of days. I'll put it in on the weekend and and give the MAF (or is it MAP? - located under BBM) a clean. It may be the problem as I remember reading that if your o2 goes or if the engine is running rich, the cat can be damaged. Mine does rattle a hell of a lot and lets out some white smoke (sometimes). There is also the smell I described...

I don't have a spark socket for the ratchet so I'll have to buy one before I can take it out for pics.

FGII-XR6 · 06-05-2008, 12:57 PM

don't "clean" the map sensor they are easy to stuff up

InfernoSR · 06-05-2008, 01:33 PM

Sounds like some of the issues i have too... so will be interested in what fixes it...

**Stav** · 06-05-2008, 05:53 PM

If you have a strong fuel smell in the exhaust then it is most likely a misfire. The other cause could be running too rich but its more likely a misfire. What this means is that the ignition system may not be firing the culprit cylinder. The causes can be bad plugs,leads or (unlikely) coil. If it is a misfire I would reccomend you check each of your plugs colours in order.The one that is most discoloured is likely to be where the fault is.Check the lead and plug on that cylinder first. Whens the last time you did the plugs/leads?

JMO · 06-05-2008, 08:34 PM

The plugs and leads would have been done a little over a year ago (14-15 months). They would be lucky to have done 10,000-15,000k's in that time.

JMO · 11-05-2008, 02:56 PM

Finally got a chance to get a snap of the sparks...

Do any of them give a hint as to which cylinder *may* not be firing properly?

bodes-sh · 11-05-2008, 11:28 PM

looking at that, i would probably go with number one, ie far right, if they are in order...the others all seem to be "fairly" similar as fas as colour goes, that one seems a bit lighter than the others tho

then again....number 4 looks a bit darker or more burnt than the other ones...

JMO · 09-07-2008, 06:31 PM

Digging up an old thread, but the problem is still there.

To date I've:
-Cleaned throttle body
-Changed fuel filter
-Changed Plugs
-Changed leads

What should I try next?

I've noticed that while in 'D' or 'N' and it's rough, if I give it a little throttle, it moves from about 700rpm to about 800-900rpm and the roughness is gone. Should I adjust the idle speed. How do I do it properly, what are the pros and cons and are there any pitfalls to watch out for?

Cheers.

Ride · 09-07-2008, 06:56 PM

How old is your oil + filter? I had a lot of built up from crap fuel and some other things, changed both and running like a dream ... had exactly the same problems.

JMO · 09-07-2008, 07:10 PM

Just took it in for a major service two days ago. Morons didn't seem to pick up on the rough idle...

EDIT: My previous post should read that it is rough in 'D' and 'R'

GK · 09-07-2008, 08:31 PM

Coil pack!

A few people have found that they've not put the leads on properly, but if you're sure that you have, then perhaps the coil pack is the culprit.

GK

Windsor220 · 09-07-2008, 08:39 PM

It may have a small air leak somewhere. I've seen a few Ford 6s have leaking intake manifold gaskets that cause a rough idle. Spray some carby/throttle body cleaner around it while idling and see if the idle changes.

Just an idea

GK · 09-07-2008, 08:55 PM

Quote:

Originally Posted by Torxteer

It may have a small air leak somewhere. I've seen a few Ford 6s have leaking intake manifold gaskets that cause a rough idle. Spray some carby/throttle body cleaner around it while idling and see if the idle changes.

Just an idea

That is a good idea! It will cost you nothing to do it.

Also check the 10mm bolts on the inlet manifold to see if they're loose. Just do it when cold of course! Perhaps do that before starting it and using rthe carby cleaner! LOL!

GK

JMO · 09-07-2008, 09:27 PM

Is the inlet manifold the BBM? How would I check to see if the coil pack is the culprit without having to buy a new one? Is it hard to install a new one? There isn't much space down there. lol

If it is a leaky manifold, how do you fix it?

Would it be worth a shot playing with the idle speed? The thing is it just started running rough one day, nothing else has changed engine wise except the 2.5" exhaust, so I don't know if it is the culprit...

bodes-sh · 09-07-2008, 09:43 PM

have you cleaned / had cleaned the idle speed controller? sometimes they need a really goos clean out, i had to spray mine out with brake cleaner and compressed air a couple of times to get all the carbon out of it...

coil pack isn't too bad to replace, you have to get it out from underneath tho...as far as checking, the only way you can really do it is with a new one..

yes the bbm is attached to the top of the inlet manifold, same thing really

EvilChief · 09-07-2008, 11:03 PM

if there are black stains alongs side the lower flange plate of the intake manifol,d near the head, your intalke manifold is mroe than like leaking. nothing too uncommon for comsodres and falcons to do, ehnce we tighten the lot at every service.

also cleaning throttle body and iac are not a bad idea either.

to test coilpacks, select D, foot on brake (pump it up), hand brake up and foot on accelerator. if it misfires, you may have a coilpack or HT lead problem. test resitance of teh leads and if less than 15kOhm, it is 95% safe to sa that you have a coilpack issue. also noticeable under heavy acceleration or high load.

JMO · 10-07-2008, 09:05 PM

I've cleaned the ISC. The 10mm bolts on the flange weren't completely tight, so I did them up a little more (except the bottom bolt on no.6 as I couldn't reach the bolt). I then sprayed the tops of them with carby cleaner but nothing seemed to change. I looked underneath to see how the cat is connected (for another thread) and saw this:

It's water (not coolant) you can see dripping from the join between the cat and the exhaust. From what I understand, water is one of the by products from the cat conversion. The cat has been making a 'rattling' sound for a while, but I can't recall which came first, the rough idle or the rattle. Could this be the cause?

I recently changed the o2 sensor that goes into the side of the engine block. Is there only one, or is there a second that could possibly be faulty?

I like to occasionally floor it (accelerator completely down) on the freeway entry ramps and there is no misfire, does this rule out the coil pack?

EvilChief · 10-07-2008, 09:45 PM

blocked cat maybe ...

blocked cat can cause all sorts of wonderfull things:

last car with blocked cat blew the exhaust recirculation valve into two pieces, rough idle, couldnt rev past 4000rpm, wouldnt shift gears, throw some sensational codes ... it was great

:

JMO · 10-07-2008, 10:00 PM

Is it more likely the cat than the coil pack? As I said, I do like to floor it coming onto the freeway and I don't remember it ever misfiring, It seems pretty smooth.

I was thinking of adjusting the base idle to about 800rpm but this has given me second thoughts. Should I try that before doing the cat or is it the most likely culprit?

GK · 10-07-2008, 10:37 PM

Leave the idle.

Can you write up an updated list in order of all the things you've done to date, so we don't have to decipher the info from the beginning of the thread?

BTW, how's the air filter looking?

Also, did you do the rev up test as suggested by EvilChief?

GK

JMO · 10-07-2008, 10:53 PM

Things I've tried to date:

-Changed air filter
-Changed ISC
-Tightened all but one of the maifold bolts
-Clean throttle body
-Changed sparks and leads
-Changed O2 sensor

As for EvilChief's suggestion, does he mean for me to completely floor the accelerator? Also was is a HT lead?

Windsor220 · 10-07-2008, 11:01 PM

Quote:

Originally Posted by JMO

Things I've tried to date:

-Changed air filter
-Changed ISC
-Tightened all but one of the maifold bolts
-Clean throttle body
-Changed sparks and leads
-Changed O2 sensor

As for EvilChief's suggestion, does he mean for me to completely floor the accelerator? Also was is a HT lead?

HT leads are just ignition leads which you replaced.

Dont completely floor the accelerator otherwise it will overpower the brake.

BIGJB · 10-07-2008, 11:02 PM

Gotta say it sounds to me like the cat may be shagged.

JMO · 10-07-2008, 11:50 PM

I've got a couple more things to try, coil for one, but the cat is looking more and more like the culprit. What I can't believe is that the mechanic didn't even pick up on the noise the cat makes, let alone the obviously rough idle....

:

Foggy · 11-07-2008, 08:24 AM

Dont forget that if the cat has started to collapse it is possible you now have bits of ceramic all through the exhaust system.

JMO · 11-07-2008, 10:22 AM

I have an air compressor, so I should be able to blow anything out the exhaust pipe. Hopefully the vacuum cleaner is strong enough to get anything out of the headers. If I take it to a shop they should clean it out for me. This is of course assuming it is the cat.

JMO · 12-09-2008, 06:30 PM

Ok. I'm bringing up an old thread but I'm still having trouble. I just had my new cat installed today and while the rattle of the old one has finally been silenced and it is a little smoother at idle, the pulsating vibration is still there.

So far I've:

-Changed air filter
-Changed ISC
-Tightened all but one of the manifold bolts
-Cleaned throttle body
-Changed sparks and leads
-Changed O2 sensor
-Changed cat convertor

I've done the coil pack test (previous page), but didn't notice any miss. It does smooth out slightly when I raise the revs to 650-700.

I've got my brothers AU sitting outside, so i could always swap the coil packs over (pain of a job :()

If not the coil pack swap, What should I try next?