idle bypass valves

[Miff]

i am having a few probs with my vhpd engine. Initially it wouldn't pass the SVA because of a duff wiring loom that left the idle bypass valve permenently powered (closed i think). Now this has been fixed but the engine speed increases to max when load is taken off it after full throttle (see previous post). The throttle is returning to closed immediately and it doesn't seem to be a problem with the throttle valves per se.

 

Could it be that the idle bypass valve is now permenently open, resulting in the problem?

 

How do i check out when the valve is open and closed? (can I?)

 

Thanks.

[DohNut]

I am not sure what your bypass valve looks like but it must have a pipe allowing air in and a pipe allowing air out of the valve and into the engine.

The in pipe may have a small air filter on it. If you remove the filter and block the hole with your finger It this affects the idle speed then your problem is probably in the area of the valve.

 

Nick

 

[Miff]

aha! have spoken to caterham and they have said that the throttle valves themselves may not be fully closing.

 

Is anyone familiar with how i check and, if necessary, adjust this?

[6XFanClub]

Take of the air filter and look down the barrels. Get someone to pump the throttle. Make sure that the butterflies are fully closing against the stops in the idle position, even when released from full throttle. If not then you will need to adjust the throttle cable. I had a similar problem with my car

[V7 SLR]

The IACV sticks. My SLR's done 16000 miles (or thereabouts) and it has played up since new. I'm now running an Emerald ECU so I can see exactly what the IACV should be doing when I plug a laptop into the ECU, but I believe that this only tells me that the ECU has told the IACV what to do and not]/i] what the IACV is really doing. I am not at all sure whether there is a feedback loop telling the ECU that the IACV has complied to the instruction.

 

For example, I spent a fair bit of time setting up my cold starting with the new ECU so that I can start it with a little tickle of the throttle until the engine fires, whereupon I can let the throttle back out and leave it alone. Problem is, I came to start it last night and it wouldn't idle. I had to drive for about a mile before stopping the car, switching off and restarting. That time the IACV must have unstuck and the car idled perfectly.

 

I haven't investigated the cause, but I'm sure it is simple to fix. I see it as one (or both) of two problems:

 

1. The body around the IACV motor is milled aluminium. It is possible that the tolerance it to fine and a little very light fettling might relieve it enough. Just make sure you don't take too much material away or it'll never close properly and will cause the engine to idle at higher revs.

 

2. The motor itself has dry bearings caused by petrol-wash (can't think of a better word). Although in theory no petrol should find its way into the IACV, it does. Take the whole IACV assy off the car and smell it. It smells of petrol. I wonder if petrol has got in and just washed away any lubricant that might have been present at the outset... but saying that, mine was never 100% happy anyway, even at the outset.

 

I have this down as a winter job. It's not critical (for me) as I can just switch off/on again after a short while and it works OK. With an aftermarket ECU you could simply disable the IACV and set the idle using the screw-stops on the butterflies, but with my original SLR throttle bodies it is actually easier to use the IACV. When I eventually move to Jenvey's I'll probably ditch the IACV altogether. It's simpler to do so.

 

Worcs L7 club joint AO.//Membership No. 4379//Azure Blue SLR No. 0077//Se7ens List Tours

 

[Julian Thompson]

Miff

 

I presume the following:

 

1) You mean the main butterflies are returning to closed with no problem.

 

2) When you say the "engine increases to max revs after full throttle" you mean if the car is stationary in the garage and you give it a blip then let it idle the rpm gradually climbs.

 

If this is correct I would start the car, get it idling as best you can and disconnect the IACV - now try whatever it was you were doing to make it do the problem and see if you have cured it.

 

One thing to remeber is that on a 7, unlike a production car, there are virtually no power supping ancilliaries like a/c, heated rear windows, miriad of other daft items, so the requirement for idle speed compensation is less than on an ordinary car.

[Miff]

Julian, correct on number 1, however, as regards point 2: the effect only occurs when out driving. The high revs occur as I go to change gear, lift off and depress the clutch. It's as the load comes off the engine that the revs climb.

 

I spoke to PTP about the problem and they said they would replace the whole lot (throttle bodies) gratis. Unfortuantely lack of time (mine) has meant that I have now given the car back to Caterham Midlands for a diagnosis. I will pass on the above info.

 

Thanks.

 

M1FFB

[Julian Thompson]

Miff

 

Mad stuff!

 

Hope they sort it for you.

 

If it is any consollation my idle is a sack of spanners and it's crap at 4000rpm but it does go like fook when you gun it!

 

Just don't take a passenger! It feels like you've got the mat stuck under the throttle!!

[Miff]

sorted!

 

The problem (if anyone was/is interested) was that the trumpets on the throttles were heating up and expanding, causing the butterfly valves to fail to close when the engine was hot.

 

Sorted now with replacement throttles from PTP, diagnosis by Caterham Midlands.

 

Miff.