High idle speed

haircutmike · Post by **haircutmike** » Tue Apr 17, 2012 9:05 pm

This is on my 4.6 RV8 TVR.

I am slowly getting all the niggling things sorted.

You fix one and another rears it's head.

I am running no lambdas and the green tune resister

Timing spot on
Stepper cleaned and viewed moving in and out
stepper well sealed to housing
Stepper connector on
Vacumn pipe connected to regulator + no splits
Rubber pipe to plenum fitted + no leaks
Car starts ok, idles cleanly at 900 rpm when stone cold and revs then gradually rise to 1600 rpm.
The air screw on the plenum is screwed down all the way, if not the more you unscrew it, the higher the revs!

Funny thing is that when the idle was normal and it started from cold, it always ran very rich till it warmed.
Now it runs cleanly from cold and when warm, idling at 1500 rpm shows 12.3 or thereabouts on the fuel ratio gauge.
Suggests huge air leak/AFM/Gerbills???

I've run out of ideas and look to you guys for an answer............

DaveEFI · Post by **DaveEFI** » Tue Apr 17, 2012 9:47 pm

Can you block off the feed to the stepper motor? My guess is it's not closing properly.

haircutmike · Post by **haircutmike** » Tue Apr 17, 2012 10:20 pm

If I block of the hose at the plenum to the stepper, it idles at 800 rpm and can be tweaked by the air screw.

DaveEFI · Post by **DaveEFI** » Tue Apr 17, 2012 10:36 pm

Sounds like either the stepper is sticking or its valve seats dirty? They are not the most reliable device in the world

haircutmike · Post by **haircutmike** » Wed Apr 18, 2012 8:46 am

Fully cleaned and moves in and out.

haircutmike · Post by **haircutmike** » Fri Apr 20, 2012 1:21 pm

Getting somewhere I believe.

Throttle position sensor was out, corrected.
AFM, correct reading.
Blocked stepper hose and adjusted air screw, idles now at 900 RPM.

Took car for a short spin, when you stop engine idles at 2200 RPM and within the next 5-10 seconds, dropps back to 900 RPM in 3 stages, 2200, 1700, 1200, 900.

Switched off engine, waited a mo, started up and it goes through the 2200-900 routine every time you start her up!

Disconnected stepper plug while engine running and problem now solved.

Why?