Idling glitches
Discussion
Hoping I can rely again on the ever helpful S' enthusiasts out there....
Last week (while the sun was still shining) took the S3 out for a blast after work - Marlow, back roads in Oxon - then back towards Reading. Great fun, great roads but Oxfordshire seem to have imposed some 'curious' 30mph limits......
Now - the request for help. Halfway round the S started misbehaving - idling at 1500 rpm plus. No other problems and worked fine on full/part throttle. Has since done the same thing each time I've used it.
Reading 'the bible' this seems to be likely to be trouble with either the 'idle stepper motor' or 'throttle pot'. Not being a mechanical wizard, can anyone advise how difficult it is to access, test, replace these things?
Thanks for any guidance, from someone who still remembers carburettors...!!
Last week (while the sun was still shining) took the S3 out for a blast after work - Marlow, back roads in Oxon - then back towards Reading. Great fun, great roads but Oxfordshire seem to have imposed some 'curious' 30mph limits......
Now - the request for help. Halfway round the S started misbehaving - idling at 1500 rpm plus. No other problems and worked fine on full/part throttle. Has since done the same thing each time I've used it.
Reading 'the bible' this seems to be likely to be trouble with either the 'idle stepper motor' or 'throttle pot'. Not being a mechanical wizard, can anyone advise how difficult it is to access, test, replace these things?
Thanks for any guidance, from someone who still remembers carburettors...!!
Reading 'the bible' this seems to be likely to be trouble with either the 'idle stepper motor' or 'throttle pot'. Not being a mechanical wizard, can anyone advise how difficult it is to access, test, replace these things?
'idle stepper motor': on the V6, I prefer to call it an air bypass valve, as it allows more air (and therefore fuel) into the system when the engine is cold (acts like a choke). They rarely fail, it's usually just dirt inside preventing smooth operation. It's easy to unplug, unbolt and clean, but make sure you get a good seal when it goes back on.
'throttle pot': or more commonly "lttle bast***"
, is notoriously unreliable, but this is often due to poor connections. Take it off and clean the contacts. Take a look at this previous thread:
www.pistonheads.com/gassing/topic.asp?t=30863&f=11&h=0
Yep, quick and easy thing first - the Idle Speed Control Valve (Air Bypass Valve on 2.8, Idle Stepper Motor on V8). This little gadget controls idle speed at all times, as the throttle butterflies are supposed to close fully. It is very susceptible to becoming clogged with oil gunge etc. and therefore does not work properly. It is located just downstream of the throttle butterflies and opposite to the throttle linkage. While you're at it the butterflies themselves could probably do with a clean.
Cheers
Ian
Cheers
Ian
Mine's an S1 2.8, and i'm now into my third week of trying to sort out idling. It seems to be ok from cold, then once warm it will hunt between 500 - 1100 rpm and eventually come to rest at 1000 rpm. Only if I slow dowm very gently through the gears, can I get it to stabilise quickly. I've tried adjucting both the idle screw and throttle stop screw at a million different settings and have cleaned / changed the air bypass valve, thermotime switch, warm up regulator and even reset & cleaned the sensor plate. From the previous comments am I right in thinking that the throttle stop screw should not be leaving the butterfly partially open on idle? Please help as my TVR grin is fast diminishing!
craigy said: Mine's an S1 2.8, and i'm now into my third week of trying to sort out idling. It seems to be ok from cold, then once warm it will hunt between 500 - 1100 rpm and eventually come to rest at 1000 rpm. Only if I slow dowm very gently through the gears, can I get it to stabilise quickly. I've tried adjucting both the idle screw and throttle stop screw at a million different settings and have cleaned / changed the air bypass valve, thermotime switch, warm up regulator and even reset & cleaned the sensor plate. From the previous comments am I right in thinking that the throttle stop screw should not be leaving the butterfly partially open on idle? Please help as my TVR grin is fast diminishing!
Sorry, I don't know.
All the previous info relates to the non-cat 2.9 engined cars (S2 & S3).
Craig, I asked the question about the role of the throttle stop screw on the 2.8 several months ago and got no replies so I left mine as it was i.e. backed out and having no effect. That way the idle is only controlled by the adjustment screw underneath the throttle body.
One area to check carefully is that there are no leaks in the hose between the air filter box and the throttle body. The air flow is monitored at the filter box so if air is entering through holes in the hose it will affect the engine running considerably.
Hope that helps
Chris P.
One area to check carefully is that there are no leaks in the hose between the air filter box and the throttle body. The air flow is monitored at the filter box so if air is entering through holes in the hose it will affect the engine running considerably.
Hope that helps
Chris P.
chingers said: Craig, I asked the question about the role of the throttle stop screw on the 2.8 several months ago and got no replies so I left mine as it was i.e. backed out and having no effect. That way the idle is only controlled by the adjustment screw underneath the throttle body.
One area to check carefully is that there are no leaks in the hose between the air filter box and the throttle body. The air flow is monitored at the filter box so if air is entering through holes in the hose it will affect the engine running considerably.
Hope that helps
Chris P.
There is a rubber collar that sits on the air filter end of the air hose, this had split and perished on my S1.I covered the entire hose in a layer of transparent silicon sealant and manufactured an efficient replacement for the split collar using silicon.Hope this helps,
Mash
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