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Idle idling!

I'm doing my Evo1 a big favour by having its original engine rebuilt, then fitting it back in. You'd think I was planning something bad for the car with

all the problems it keeps throwing at me.

The latest is the idle control valve.

All was fairly well until I had to return the new engine, fitted in the car, to the rebuilders to fix an oil leak. The throttle body idle screw fell out on the way there, never to be found, it never had a lock nut, so it must have unscrewed itself and fallen out.

Jim at Chester quickly shipped a replacement.

With Jim's new screw and locknut fitted, the car wouldn't idle unless the screw was completely removed! After 2 days messing about I suspected the idle control valve, so I ordered one from Eddie at AECar. When the new valve was fitted, the car idled happily, but at 1500rpm!

I checked for air leaks, but there were none. Something was obviously not right.


The idle control valve is sent a voltage from the ECU, which has read the temp sender. This operates the idle valve's internal solenoid, opening and closing to meter air into the inlet manifold behind the throttle body, when the throttle butterfly is closed. 

The air input is further adjusted by the throttle body idle screw, which adjusts an opening in a bypass channel which also bypasses the closed throttle butterfly.

This idle valve is not something I have much experience of, but I needed to

understand what, why and how.

The idle control valve in its mounting.

Valve assembly lifts out of pipe junction


Original valve bottom,

AECar valve centre,

Chinese valve in box

I enquired about the idle valve adjustment on the Evocorner forum, this got a quick response from member Kiwigrale, his reply included a link to an AutoDynamix site page, where they had stripped down a Weber idle valve.

The Weber originals are not available, and the replacements are mostly made in China, the Cosworth article explains how you can put the better quality

old parts in the new Chinese valve.

Click their logo to visit the valve page.


For research purposes I also bought a £29.99 valve on Ebay, this item was from a vendor in China which I planned to return. The new replacement from AECar was expensive at over £90, which also had a Chinese feel to it.

I plugged the valves in on the car unmounted and tested each one, both new valves quickly fully opened with ignition switched on, then slowly closed when I started the car up. The original valve didn't move when the ignition was turned on, it stayed closed.


At the bench I stripped the valves down following  AutoDynamix instructions, taking care to mark which springs went where, the inner spring is stronger than the outer. Not surprisingly I did find the original Weber was of higher quality than the two replacements. The AECar valve centre post was off centre, it did operate on the car but I wasn't sure of its precision. The Chinese valve had slack around the plunger, and had 2 small squashed springs on the inside instead of a 

strong single one.

After testing the electrical resistance on the valves, and finding not much variation, with the new Chinese valve having the highest resistance, I assumed the Weber valve's solenoid had seized, so I fitted the Weber's superior plunger and correct springing into the AECar valve, again as AutoDynamix suggest.

The Chinese valve looked to have the same body as the AECar one, but the moulded plastic top was the wrong way around for the Delta installation.

The Chinese plastic top also had no guide pin or clip points on it, 

so it could be legitimately returned.


The original Weber valve is on the left, it has a well finished sleeve valve which fully closes in a neat flush position.

The AECar valve on the right, doesn't have the same neat full width sleeve, the pillar is off centre, it has a plastic washer below the adjusting nut, and is generally of a poorer finish than the original.

The Weber inner spring is stronger than the outer, which pushes the valve into the closed position, the others seem to be the same strength, with the Chinese valve having two outer springs squashed together, by mistake, or to make one stronger spring. This wasn't working properly at all!


Images above show the various points of rooting around inside these valves, and the varying quality of the components.

I've done as AutoDynamiks suggest, and use the better quality innards in the new outers with a working solenoid action.

The car now starts and idles in the correct way, have a look at this YouTube vid...

I'm afraid once again the quality of a part available for our cars is disappointing, I suggest you check any parts you

purchase for quality, and correct fit and function, before you install the item.

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