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Old Corolla

Corolla Diesel Srd With Very Rough Idle.

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My '94 SRD suddenly started using more fuel a couple of months ago, the MPG dropped from the usual 40/42 to 30.

I've checked everything I can think of, there are no leaks that I can see and I've changed the fuel, Oil and air filters and of course the Oil. I also added a bottle of injector cleaner at the last fill up which I do every now and then anyway.

Now it has started idling very roughly once the engine is warm and I mean rough, the whole car shakes.

I put it in early for the MOT last week and it passed with just an advisory for a small leak from the exhaust. I thought it would fail as it was attempting to shake itself to bits. It passed the emissions test with flying colours and the MOT inspector said he couldn't fail it for being "a bit rough".

He said it might be sucking in air through a small crack in the fuel lines so I sprayed loads of WD40 around them to see if the revs picked up but nothing happened.

Any ideas as to what I could check next would be appreciated, thanks.

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If you have checked the other things mentioned in the other thread, then you need to look a bit deeper into it.

The idle speed can be adjusted by the screw and locknut - bring it up to 750~850 rpm to start with.

With a decent idle speed, crack each injector pipe off in turn to see if the idle speed drops evenly on all 4 cylinders.

If one cylinder doesnt drop as much, that will narrow it down a bit.

Fuel leakage is normally the main cause of rough idle/ high fuel consumption, so check it again including the seals on the diesel filter.

When was the cambelt last changed ? Has it jumped a tooth to give you a poor tickover/ high fuel consumption .

Failing that, you will need to get the pump timing checked and the injectors tested.

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Thank you, that's given me a few things to work on.

I hadn't thought about the cambelt but it was changed at 188000 miles 4 years ago so according to the service schedule it should be OK for another 30000 miles, but I'll get it checked anyway.

I've fiddled with the idle adjustment and it only starts to run smoothly at around 1200 revs.

Thanks again

Ian.

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