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rough idle, high emissions, low mpg

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cornish4475
Posts: 12
Joined: Wed Oct 27, 2010 11:55 am
Year and Model: 440 GLT Turbo A '95
Location: Truro, Cornwall

rough idle, high emissions, low mpg

Post by cornish4475 » Mon Nov 08, 2010 12:48 pm

My car is a '95 440 glt turbo auto, 101,000 miles found on ebay. Everything works and she's lovely, BUT......
She runs a rough idle (up and down from 500 to 1100rpm) hesitates on sudden acceleration, uses loads of fuel (currently 19.1 average!) The idle is better, in fact sometimes good, when cold and gets worse as she warms up, she runs/drives poorly when cold getting better when hot.
Took her for an MOT and got fails on two things, rear brake pipes corroded (not a problem, all done), and emissions (turning into a problem!) Now i'm guessing the idleing/running rubbish and emissions fail are the same problem.
The o2 reading was high, (1.24 test limit is 1.03), the hc reading was very low, as was the co2 (this was actually 0.01).
The low hc and co2 lead me to believe the cat is working properly. I've serviced her, new plugs and leads, fuel filter, air filter etc.
I've come up with a few possibles, but any other ideas or pointing me the right way will be appreciated.

Faulty lambda sensor. (but i thought the emissions readings don't suggest this but i'm not sure)
Leaking exhaust manifold/turbo/downpipe. (can't feel/see any)
Faulty MAF (cleaned with electrical contact cleaner, runs even worse with it unplugged)
Faulty ECU (i really hope not!)
Leaking injector/s
Thanks for any help in advance.
Rob

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Re: rough idle, high emissions, low mpg

Post by jblackburn » Mon Nov 08, 2010 1:14 pm

Check first for any vacuum leaks, as they can definitely cause issues as well.

However, this sounds to me like a bad (front) O2 sensor (and that's not usually something I jump to), but this is what makes that stand out:
The idle is better, in fact sometimes good, when cold and gets worse as she warms up, she runs/drives poorly when cold getting better when hot.
The O2 sensor doesn't give a reading until it warms up first.
'98 S70 T5
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cornish4475
Posts: 12
Joined: Wed Oct 27, 2010 11:55 am
Year and Model: 440 GLT Turbo A '95
Location: Truro, Cornwall

Re: rough idle, high emissions, low mpg

Post by cornish4475 » Mon Nov 08, 2010 1:39 pm

Thanks for your input. My Lambda sensor (o2 sensor) is of the pre heated type (fuse 13 on the board) but when the weather improves i'll check to see if it's got voltage through the fuse when cold.

The rough idle/poor running doesn't disappear completly at any point just improves under certain conditions.

Another thread states that my car being a turbo it won't have an obd unit, but i'm sure the thing is in there. Top of the suspension mount next to the battery. Think i'd best have a look!

cornish4475
Posts: 12
Joined: Wed Oct 27, 2010 11:55 am
Year and Model: 440 GLT Turbo A '95
Location: Truro, Cornwall

Re: rough idle, high emissions, low mpg

Post by cornish4475 » Tue Nov 23, 2010 1:39 pm

I didn't have much luck at the garage, but a local scrapyard had a 440 turbo, so i had most of the fuel injection system.
The new ecu went in first, which cured the problem up. It now runs perfect.
Thanks for your help Bill,

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billofdurham
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Re: rough idle, high emissions, low mpg

Post by billofdurham » Tue Nov 23, 2010 3:09 pm

Good to know you have it sorted. Thank you for the update.

Bill.
Work was good - retirement is better.

1996 850GLT 2.5 20v Estate Manual.
1995 Peugeot Boxer 2.5Tdi Autosleeper.
Previously:
1984 244DL, Manual, Beige.
1987 744GLE, Manual, Green.
1991 960 3.0 24v, Auto, Silver.
1994 940T Wentworth, Auto, Blue.

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