Cold Start Advice Please ( Stepper Maybe)

[anonymous-user]

Managed to shear the thread off the stepper on sunday after cleaning it( With Fingers Only ).
Ordered new one Part No ERR5199. Is this the correct one or have i made a mistake.
The main problem however is since fitting the new one the car will not start without throttle pedal assistance or maintain idle when cold.
I removed the stepper again and can see it moving in and out with the turn of the ignition key once up to temp the engine will maintain a steady idle.

Have i missed something obvious.???
What else effects the cold start up idle speed.

Any advice greatly appreciated. Thanks

[Alexdaredevilz]

I got same problem with mine, wont start unless I give it some throttle and hold it to keep it idling,

Its as good as gold when warm

Ive changed

Stepper motor
Spark plugs
Leads
Cap
ecu temp sensor
Checked all wiring
Checked all fuses

I got a Steve Heath code reader that flags up nothing!

[anonymous-user]

Thanks for reply.

Yes thats what mine is doing once warm great, but until then it dies as soon as i release throttle pedal.
I havent changed as much as you have but it was running great on friday albeit with a bit of shunting ( thats why i cleaned the stepper ).
Is there any way the replacement steppers are a different overall length and not actually seating.
Or is there any thing else temperature related that can cause these symptoms.

[scruggs]

Well there is a clue there. If all you have changed is the stepper then that has to be the first point of doubt.

I am not as wise as others on this forum but I would consider checking the length of movement of the new stepper against the old one. Keeping your foot on the accelerator when cold suggests a fuel enrichment issue which the stepper is supposed to help with.

[EGB]

Mine sometimes inclined to do the same. Give it a rev to 2000rpm to 'clear its throat' and oil splash the cam.
Sometimes when warm, rpm used to fall to 200 and stalls, at traffic lights. Solved by a 2mm thick plastic spacer under the plenum throttle stop. Keeps the butterfly open just a tad to maintain 900 tick over. Rover 3.5s had a handy screw to do this. Stepper is sometimes slow and lazy to correct tick over.

[TV8]

I had the same problem plus it was running lean on the rolling road. Alex had a look at with his fault reader and we found nothing. Dan Taylor suggested trying a different afm and ia known good one worked a treat. That sais, I hadn't changed anything before hand.

[TVR Beaver]

scruggs said:

Well there is a clue there. If all you have changed is the stepper then that has to be the first point of doubt.

I am not as wise as others on this forum but I would consider checking the length of movement of the new stepper against the old one. Keeping your foot on the accelerator when cold suggests a fuel enrichment issue which the stepper is supposed to help with.

No it's not... all the stepper does is move back into it's housing when cold to give you more air to keep the tickover up.. it them closes when the engine get's warm....
The enrichment is done by the ECU and the amount of fuel (pulse length) pumped in....

[Hedgehopper]

Why not try it with the old stepper motor and see if it runs as before? When I sheared the threads on my motor I superglued them back on again as a temporary fix and a year later they're still going strong. I also replaced the gasket with an O-ring which seems to make a good seal without the need to tighten too much.

[carsy]

To re seal it making it air tight, just put some ptfe tape on the threads.

[anonymous-user]

Thanks for all suggestions.

Have just stuck the thread back to the body with scotch-weld 810.
I will have to wait to see if it holds before i try it.

Anything worth ago at the moment as its begining to test my cool.
Still dont see why the replacement doesnt work it does motor in and out.

Neil

Edited by anonymous-user on Friday 30th March 12:33

[blitzracing]

Some of the pattern (read chinese) steppers dont retract far enough to let air in as the control rod is too long. You could try packing the stepper thread out 3 or 4 mm (Sump washer fit from memory) to make the whole unit sit back a bit in the plenum that should open up the air gap. The exact position of the stepper body is not critical as long as when the cones fully retracted it lets enough air in to run the engine when cold.

[anonymous-user]

Latest Update.

Well after sticking the old stepper back together i can report that the engine fired first turn of the key.
Most importantly idled nice and steady starting at about 1500 rpm and dying down to just under 1000rpm.

Before i refitted the old one i compared the dimensions of old and new. The new one has 2-3mm shorter thread than original. So it looks like this was the cause of all the problems.

Must agree with Hedgehopper it seems to have done the trick,

Thanks again to all

Neil

[Alexdaredevilz]

Interesting .......

[blitzracing]

Which thread? The one on the body, or the one on the central shaft? (trying to picture the effect here...) If its the central one, you may be able to swap the two as its possible to get the shaft out.

[Alexdaredevilz]

Sounds like I need to cut the thread down on mine

[anonymous-user]

No the opposite.

The thread on the body on the original is longer than on the new one.
Which means the cone on the valve actually sits further in the housing enabling it to shut the airflow off.
At least that looks like what is happening.
Similar to the way an old fashioned choke used to work.
I will take it back out tomorrow and take some measurements and photos.

[blitzracing]

That makes sense, I knew the cones where not going back far enough, but had assumed it was the shaft that was wrong, not the body. I reckon you could still get away with packing the thread out with big washers to bring the body back, as long as its airtight.

[Alexdaredevilz]

But blitz

Packing it out would make it worse going on what's been said

[carsy]

Alexdaredevilz said:

But blitz

Packing it out would make it worse going on what's been said

Yes i was thinking the same.

[blitzracing]

No, you pack the the motor backwards with washers so it moves back from the air hole in the plenum (and move the flow control cone with it) , so effectively you allow more air in. I dont think Im going nuts. .