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prox71

MKIV efi xr3i 'jerking'

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Car jerks a lot when trying to maintain a speed of around 20 to 30. 1.6 xr3i 86000 on the clock.

Have replaced spark plugs, oil and filter, ht leads, cambelt, fuel filter, potentiometer. 

car runs ok in fourth gear doesn't happen then.

Any ideas?

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Mine is the same lol not too jerky but enough to notice if trying a constant speed. I've changed all the things you have mentioned too. And in just about to fit a new coolant sensor for the ecu so it recognises whenit's warm etc for fueling. I'll let you know how I get on when I got it. 

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Check the base idle setting and fuel mixture. These were renowned for drivability issues. Is the idle speed control valve on the bulkhead or on the inlet manifold?

Edited by Paul Grainger

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some time ago when I tried looking for the idle speed control valve, but believe there isn't one? theres a potentiometer, but have replaced this

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It will be there somewhere......

The very early EFIs had a Hitachi valve mounted on the air box. These were the worst and a modification came out to mount it on the baulkhead with a piece of hose running to it. Then they were modified in production to include the valve on the air intake throttle body which was a lot better.

The potentiometer you have replaced is the one on the inner wing I pressume? This is to adjust the fuel mixture which can only be done with an exhaust gas analyser. 

There is an air bypass screw on the throttle body. Try adjusting this to get the idle speed to sit at 750rpm with the idle speed control valve disconnected (Unscrew to speed up). Then reconnect the valve and adjust the potentiometer to to set the fuel mixture.

Most garages should have an exhaust gas analyser and only takes 15 mins so shouldn't cost much.

Cheers

 

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yes potentiometer is on inner wing

located iscv it is on the back of the drivers side suspension turret 

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Ok. So yours is one of the early ones which has been modified.

Check the base idle as described previously. If on the inner wing by the potentiometer there are two black wires with spade connectors then join them together. This will make the cooling fan run constantly while you adjust base idle

Cheers

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have adjusted the base idle as suggested, doesn't seem to be any better

could be the idle speed compensator sensor, is there anywhere you can get these?

thanks for your help 

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cheers pal, changed the plugs seems to be ok now, the plugs I took out were FR5DC, they have a gap of 0.8mm, FR6DCX have a 1.1mm gap, someone mis-described them on ebay, 4 years of jerking around has left me with the shakes though 🤣

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