High idle ...what am I missing ???

[gmw9666]

Right then chaps, last few jobs done ready for the fest but I'm struggling with a high idle

All ideas are welcome

Here are the symptoms......car starts ok in 3-5 seconds and coughs into life. Needs a bit of throttle so doesn't stall then idles at about 1050 ish.........runs at that level for a bit then goes up to 1200

By this point on the road and fully warm when slowing down to a stop the revs drop and the car stalls. She will re start straight away no issues.

The AFM screw thing is out 3 full turns and still smells a bit rich

I've been over all air pipes for leaks with wd40 and nothing there

I had a new temp sender so fitted that and still the same

Checked all plugs and gaps and leads with known parts and no difference

I've currently tweaked the idle screw so now she won't stall but there is clearly something amiss

What do we think chaps?

[gmw9666]

Forgot to mention this is just an idle issue........driving and accelerating is frankly excellent (even compared to the 420!) there is no hesitation or lack of power or misfires

Yes, have been sucking / blowing hose as well.......mmmm tasty not!

One other thing, the plenum butterfly when closed appears to be fully closed, can't get a feeler gauge in

[gmw9666]

Wedg1e said:

Frayed, kinked or badly routed throttle cable holding the throttle open a tad?

Cable routes fine and moves without sticking, nice and smooth

There does appear to be a little bit of play on the linkage pivot, not a lot but a little

Will tweak the butterfly and report back also

[gmw9666]

Sireatalot said:

Morning Glen.

I had symptoms similar to this a while back where the wedge would start / run / accelerate all fine but when warmed up and coming to stop at lights etc.. it would want to stall and the revs drop into the 100 / 200 range..

It turned out to be my vacuum unit's ( on the dizzy) diaphragm had perished and not controlling the revs like it should be..

Replaced the unit and the pipe going to the plenum and all is back to normal and it hasn't stalled since..

Taking the hose off the plenum to the dizzy.........its is clear with no splits........how hard should it be when sucking to hear the dizzy diaphragm flap move..........I'm giving it all my might and only then can I hear a small flap noise........should it be easier therefore is it stuck a bit? Would this cause the high idle?

[gmw9666]

Right, I just adjusted my flap a thou and reset TPS and now running at 2k idle with the idle screwed all the way in

Got me thinking this is all to do with the TPS or the linkage

So lets look inside my TPS, mmmm, one side almost all the carbon has come off and the copper thing has worn its balls off

Gave it a clean and popped it back on and the car runs back to high idle 1200

Frankly I think I'll worry about it after the fest when you guys can have a look for me :-)

[gmw9666]

The Hatter said:

I thought the throttle pot had to be set to a precise value at idle (325 mV with a tight tolerance I think); isn't that to tell the ECU to go into 'idle' mode? Not that I know what 'idle mode' would do... ignore the AFM perhaps?

exactly my thought, the TPS tells the ECU how rich to run, I'd set the voltage but given all the carbon on the track is gone it was this that got me wondering when slowing down the TPS is freaking out sending odd signals to the ECU.....and also why when driving she is just fine.

May try to borrow a know "good" TPS

Also reading HJ2's pages my TPS came apart very easy making me think its been open before and therefore could potentially also cause an air leak......I had not thought about the butterfly spindle as an air leak possibility. It does have some play in the linkage side.

More thought me thinks...

[gmw9666]

Convert said:

Like Ian says, unplug it and see what happens to idle speed. The dodgy tracks can't send spurious signals if they're unplugged.

not a great deal, unplug it and its very similar

[gmw9666]

Well progress

Cleaned and refitted the TPS, re set the butterfly to 100% shut as it was before and as all SD1 engines are recommended (my linkage / early 350's have a different linkage as I've found out hence the different / larger TPS)

Set the TPS to the correct voltage, unscrewed the idle then hit the road to warm the old girl up

Parked up and tweaked the idle to as low as she would go (1050 rpm) with 3 turns out on the AFM (my gut feel) then gave her a good spanking

Drives great, no hesitation, idle keeps at 1050 so frankly its not as low as others, for now she goes like a train

So lets see what the rolling road marks her before twiddling with anything else

[gmw9666]

Looks like we have lift off

Spotted a cheeky SD1 plenum / manifold on eBay going cheap, noticed it still had the TPS attached

Arrived today in the post and stripped it to compare condition of mine as shown in an earlier pic

Looks like new :-)




Reset everything and look what I got, whoo hoo




Whilst I was at it the linkage on the plenum I bought had zero play in the bearing so swapped that over





Throttle response is lightening now, quite pleased with myself

[gmw9666]

mrzigazaga said:

Well done mate......The TPS is rarer then kryptonite..In fact i bought a plenum bundle with injectors..Trumpet base, Wiring loom and...A TPS and it works...It was worth it just for that....Ziga

That rare I was able to buy 2 as well as an adjustable ECU lol ;-)