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

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

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Discussion

Wedg1e

26,760 posts

264 months

Wednesday 1st July 2015
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The throttle pot's main function is for acceleration enrichment, you can unplug it and the car will run pretty well without it - it certainly wouldn't normally affect the idle speed.

The Hatter

988 posts

169 months

Wednesday 1st July 2015
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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?

gmw9666

Original Poster:

2,734 posts

199 months

Wednesday 1st July 2015
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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...

Convert

3,747 posts

217 months

Wednesday 1st July 2015
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gmw9666 said:
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...
Like Ian says, unplug it and see what happens to idle speed. The dodgy tracks can't send spurious signals if they're unplugged.

gmw9666

Original Poster:

2,734 posts

199 months

Wednesday 1st July 2015
quotequote all
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

GOG440

9,247 posts

189 months

Wednesday 1st July 2015
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This might sound like a daft suggestion but have you checked that you actually have a thermostat in? Mine had a high idle (1200rpm ish) caused by the lack of thermostat to tell the ecu that the engine is warm, effectively you are running with the choke out all the time (if you are old enough to remember a manual choke)

Unfortunately mine was removed by a previous owner to cover up a fked head gasket which cost me ££££ to sort

mrzigazaga

18,534 posts

164 months

Wednesday 1st July 2015
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Be careful though as removing the thermostat housing has already nearly cost one Wedger his day out in his P&J...I still think you have an air leak....Check all the hoses on the air side ..I can see that you don't have a clip on the plenum end of the idle control valve housing...Also i can't see any throttle return springs...There should be one at least..Better with two though...Perhaps the butterfly/Throttle plate is not returning properly...Mind you as said about the throttle cable...Mine started to stick and i thought it was the throttle housing but i felt up at the top of the accelerator pedal and could feel some frayed cable...

gmw9666

Original Poster:

2,734 posts

199 months

Wednesday 1st July 2015
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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

Original Poster:

2,734 posts

199 months

Wednesday 8th July 2015
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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


mrzigazaga

18,534 posts

164 months

Wednesday 8th July 2015
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Well done mate...clap...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

gmw9666

Original Poster:

2,734 posts

199 months

Wednesday 8th July 2015
quotequote all
mrzigazaga said:
Well done mate...clap...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 ;-)

KKson

3,395 posts

124 months

Wednesday 8th July 2015
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gmw9666 said:
mrzigazaga said:
Well done mate...clap...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 ;-)
I've got two complete plenum/inlet manifold/injectors/wiring loom set ups, one with the older TPS and one with the latter one (for mine) Two complete set ups for £40 off flea. Billy bargain and useful set of spares in case anything breaks.

Didn't manage to get an adjustable ECU though.

adam quantrill

11,535 posts

241 months

Wednesday 8th July 2015
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Don't chuck yer old TPS's away - in case they can be reconned.

With your old one, you can shift the wiper to one side by taking off the plastic mount and screwing it back down with some fine self-tappers. However with two of the bumps rubbed flat, it won't last too long because the bumps now have sharp edges which will cut through the track again.

Both myself and HonestJohnToo have created replacement TPS solutions with aftermarket pots. My one was rated for a million operations so should last 27 years of driving every day!