Sticky tick-over

[phillpot]

Cars running a real treat since top end overhaul (and few other little jobs) except when I lift off the accelerator engine drops back to about 1400 revs then takes couple of seconds later back to 1000.
tried my spare throttle pot, worse, stops at 1500 before dropping back. with pot un-plugged seems to drop back to about 1250 ?
Have tried my spare idle valve (and every permutation of the two). Cable definately got some "slack", linkage definately free and not sticking, I'm convinced its an "electronic" problem but, having said that, am running out of ideas.
Does the larger of the two temperature sender things screwed into the front of the inlet manifold have anything to do with it ?

Timing could be a little out (had dizzy out) tried resetting as per an old "car mechanics" article but left it miles out, would hardly run at all so set back to the paint l marks I put on the dizzy before removing

Would be very pleased to hear from anyone who's had this fault, and more importantly, cured it (taking to garage, paying lots of pennies and not knowing what they did doesn't count) !

Mike

[Griffinr]

Sounds like too much air getting in either due to a leak or the throttle butterfly not closing fully. Mine did this for months plus a few other strange things until I reset the throttle stop. The butterflies should be completely shut at tickover as all the tickover air is suplied by the idle valve.

Rob

[phillpot]

Thanks for that, will try putting old throttle butterfly assembly back on tomorrow.

[Jaye R]

Mike

If it's just a second or two before it drops to idle then it's the same as mine - it's always done this.

I've always thought it was 'normal'.

Cheers
Jaye

[Harry1972M]

Mine was like this and like Jaye I assumed it was normal - cleaned the MAF's whilst trying to pinpoint something else and this cured it.
Graham

[phillpot]

SUCCESS !!!!

Thanks Rob for pointing me in the right direction,
Throttle housing, butterflies etc. had been apart for "sandblasting", so loosened screws, re-aligned butterflies, tweaked and twiddled operating linkage (have made myself a straight J plate)and all is Hunky Dory !

No longer feels like cruise control is on when I lift off and ticks over sweet as a nut at about 850/900.

You guys who said "yours does it" really ought to have a go at sorting, car so much nicer to drive, now just got to sort rattly tappets, and yes it is tappets not blowing exhaust

Mike

[Griffinr]

phillpot said:

have made myself a straight J plate)and all is Hunky Dory !



Mike

Glad your sorted, the throttle is quite a fiddle to set up right. Did you make your straight throttle plate up from scratch or modify the existing one as I've been thinking of doing mine.
Also, does it make much difference?

Rob.

[Barkychoc]

I'm sure someone posted on another thread in the last few days that the straight throttle plate was a ford part that they still have stock of.

[phillpot]

Modified a "standard" one, filed the one edge out straight then brazed a little fillet in to the other side.
Obviousley got to be very careful, don't want it sticking

Tried to remove the pivot bush to save melting it bit appeared to be moulded onto the metal so cut it off and made metal replacement from a long M8 nut (like used to join all-thread), again brazed into place.

And yes, was worth the trouble, throttle response far more "snappy" !
(put old J plate on during my jiggling around over last couple of weeks and it was horrible, foot half way down before anything happens