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Old 12-22-2009, 10:25 AM   #1 (permalink)
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Default Random Misfire at idle

I bought a 04 Land Rover disco about 6 months ago and had done a lot of work on it: Head gaskets, cam shaft, timing chain, rods, lifters etc...

One problem I've been struggling to fix is that at idle the engine has random multiple misfires. If I give it some gas, it stops misfiring. This happens when the engine is cold or hot. If I get off the highway and am at a red light, it can happen. It's very random.

I tried troubleshooting it as a vacuum leak, but didn't have any luck there.

Some things to note:
New coil pack
New Wires
New Plugs

It runs fine, it just has trouble at idle.

Any ideas?
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Old 12-22-2009, 10:32 AM   #2 (permalink)
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how old is the air filter?
what about maf?
what grade fuel are you using?
what type of plugs?
what type of wires?
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Old 12-22-2009, 10:35 AM   #3 (permalink)
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how old is the air filter? - Pretty new
what about maf? - It's plugged in, what else to know here?
what grade fuel are you using? - 93
what type of plugs? Bosch
what type of wires? Bosch
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Old 12-22-2009, 10:35 AM   #4 (permalink)
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Also, check the idle control valve is free and the hoses tight, and the vacuum connection for the brake servo is good.

Peter
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Old 12-22-2009, 10:37 AM   #5 (permalink)
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Those are actually the 2 last things I checked, thats what I was thinking it was.
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Old 12-22-2009, 11:40 AM   #6 (permalink)
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Any lights lit up on the dash? Did you check for fault codes with a scanner?
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Old 12-22-2009, 12:40 PM   #7 (permalink)
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When it misfires the Check Engine light flashes. I let someone borrow my scanner, so I don't have it at this time, but I was getting random misfire codes before when I checked.
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Old 12-22-2009, 12:54 PM   #8 (permalink)
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Go to the ZOne and they will read them for free if you can...

The "maybe" list will start with:
Wires
plugs
mafs
coil
gas
See a trend!

What are the brands you used to replace wires etc?

How has the coolant level been? Any funny smells out the tail pipe?

How many miles, last tune up, have you looked at the plugs lately?

I went through three sets of wires till I got it right, then the MAFS went, just after the HG's were replaced, which was just after the alternator went with the battery, the coil was replaced by throwing parts at it, just before the throttle body gasket started to erupt, the PAS pump still leaks and hard to turn after replacing it, the HDC light comes on randomly and the sunroofs leak like a B when the snow melts and right around the time we replaced the fuel pump thinking the hesitation was lack of fuel, but it turned out to be bad plugs for the third time trying to save a buck or two on plugs. ;-)

Need more data / fault codes really.
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Old 12-22-2009, 11:59 PM   #9 (permalink)
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I'd have thought that the MAF (Mass Airflow sensor) could be eliminated if the truck runs OK otherwise, same with the plugs and leads.

The SAI (Secondary Air Injection) system might be worth looking over, especially as there is a vacuum connection between the vacuum reservoir and the inlet manifold. The system normally only works at cold start.

Lastly, there is the charcoal canister purge valve on the driver's side of the upper inlet manifold, and while you're there, run a spanner/socket over the bolts holding the plenum onto the manifold and those holding the whole thing down to the manifold.

Peter
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Old 12-23-2009, 09:21 AM   #10 (permalink)
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Pitch the Bosch plugs and get some Champion 318s.
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Old 12-23-2009, 09:33 AM   #11 (permalink)
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So I had 1 side of the SAI disconnected because I needed a new SAI plug. I've got that and I'm gonna throw that on today to see if that is contributing.
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Old 12-23-2009, 10:52 AM   #12 (permalink)
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First - A flashing ses light means the cats are melting internally. Its smart to shut it off when that happens.

Second - Bosch plugs are shit. I would bet both of my testicles that when you put in the right plugs, your problem will be solved.
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Old 12-23-2009, 12:00 PM   #13 (permalink)
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Quote:
Originally Posted by Elemental View Post
First - A flashing ses light means the cats are melting internally. Its smart to shut it off when that happens.

Second - Bosch plugs are shit. I would bet both of my testicles that when you put in the right plugs, your problem will be solved.
Echo that! E
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Old 12-24-2009, 06:44 AM   #14 (permalink)
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Quote:
Originally Posted by Elemental View Post
First - A flashing ses light means the cats are melting internally. Its smart to shut it off when that happens.

Second - Bosch plugs are shit. I would bet both of my testicles that when you put in the right plugs, your problem will be solved.
It's easy to suggest something when it was introduced two posts before
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Old 01-31-2010, 07:16 PM   #15 (permalink)
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So I replaced the plugs with the OEM plugs, and same thing... What the heck?!
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