Slight misfire at light throttle

[ghaddon1701]

Hi all,
My Motronic injection GTi has devoloped a slight misfire at very light throttle openings. Most noticable at about 50mph on the level. Also acceleration can be a bit inconsistent up to 4000rpm then it pulls ok. Ticks over ok and pulls well at full throttle. I was thinking along the lines of throttle position sensor. Although I haven't tested it yet. I have come to this conclusion because the leads and plugs were changed not long before I bought the car. I changed the fuel filter at the weekend aswell thinking that might help but no. Any ideas anybody. Thanks.

Regards Graham

[ghaddon1701]

Also forgot to say. Can be slow returning to idle when warm. Thanks.

Regards Graham

[ghaddon1701]

Ran the engine in the dark with the bonnet up tonight. At least two of the plug leads are tracking at the spark plug ends. Lights the spark plugs up a treat. Plugs and leads change next I think.

Regards Graham

[docchevron]

they can be a bit slow to return to idle anyway, but it might be worth getting the FPR checked too..

[Way2go]

Sounds like the problem that developed with my GTi but it was not ignition it was the injectors that were getting gummed up. The injectors have a mixture of different spray patterns for different duties. Had them serviced with new filters, 'o' rings , pintle caps and an ultrasonic clean to return it to its responsive best. Makes for very easy starting too.

[KevR]

Definitely worth checking the TPS - I've got the same problem on my BMW 1100, which also uses a Moronic Fi system. Pretty sure the TPS is on the way out - already changed everything else!

[ghaddon1701]

Changed the plugs and leads no difference. Changed TPS no difference. A full tank of super petrol and things seem much improved. May run some injector cleaner through it. Fingers crossed it stays ok.

[Melchior]

I'm really glad you posted this as I have a pretty similar problem with mine. Can't yet figure out if it's spark or fuel causing the problem but I was leaning towards spark - suspecting faulty coil, ignition module or wasted spark distributor.

However this seems to have started since running very low on petrol so I'm waiting for pay day so I can fill her up and throw some injector cleaner in there (although for years I swore I would never waste money on that stuff again!).

Please keep us posted as to how this pans out for you, fingers crossed it will be ok

[ghaddon1701]

Mine is still behaving itself. I have some forte specialist injector cleaner running through the system at the moment. See if that keeps it running ok.

Regards Graham