Engine 850: B5234T/2.3/20v/T5: High idle / slow response off throttle?

[Stu B]

Hi All,

Hopefully someone can advise on this. I've done lots of work on my 850 T5 over the last few months, changing clutch, vacuum hoses, PCV, suspension bits and pieces and various other jobs. I'm sure it's ended up with a higher idle than it used to have and seems to have a delayed response when you release the throttle (i.e. the revs remain higher between gear changes)?

It was idling just about 1,000rpm when warm for the last few weeks, so I checked the throttle cable movement is ok, lubricated it a little at the throttle body end checked all the vacuum hoses are seated ok, which they appear to be last weekend. Idle is now approx. 900rpm which makes be think perhaps the cable was sticking?

I can't recall exactly, but I'm sure it previously idled at something like 600/700rpm? What is the correct idle speed for a standard T5 and what should I be checking? Dirty throttle body? Air leak somewhere maybe? Presumably there is some kind of air bypass / idle valve stabilising somewhere I may need to clean out? I will consult the Haynes!

Aside from that, the car runs great and to be honest, if I didn't recall it previously idling lower and having a sharper throttle response, I doubt I'd notice.

Thanks
Stu

[DunkinBiskits]

around 750-810rpm

adjusted the throttle cable in your recent work? make sure theres a tiny droop in the cable when its at the base point. did this myself and was blaming the ICV for a few days. then check the throttle plate and saw it wasnt shut. id just fitted the 3" TB so the idle grub screw needed adjusting to suite the new cable assembly it was mounted to.

other than that check the base of the vacuum tree - it has an O ring into manifold, also that all hoses you replaced are still on the barb they live on. remember the blind one behind the power steering pump that goes onto manifold.

[Stu B]

Hi,

Thanks for the reply and info, much appreciated. It does feel like the throttle cable may be a little tight but I haven't adjusted it, I did have to release it to remove the inlet manifold with the throttle body attached for the PCV job though.

Vacuum tree is a good idea too as I definitely did some messing around in that area changing the little vacuum hoses and fitting new, I didn't release the tree itself but many well have disturbed it somewhere so will have a look

[Stu B]

Hi,

Just to update on this, I had a quick nose around after I posted and couldn't find any obvious vacuum leaks or anything amiss, and the throttle cable looked to be working through it's travel correctly and returning to it's stop. I didn't want to disturb too much as the car was running well and I was off on a 1000 mile plus week long trip to the Isle of Skye.

The Scotland trip went really well, but approx. 300 miles from home on the return leg, the emission warning light (orange light with green lambda sign) came on. The car still ran fine, was returning decent mpg but had been smelling a little rich and still with a slightly high idle at this point for a day or two when cold starting in low temps up there. Again, couldn't see anything obviously wrong and as it ran well I drove home so need to investigate further now as it's likely all related.

Am I right in thinking the first port of call is to read the fault codes? My car has the little connector blocks with the red flashing lights behind the drivers side headlamp, are they read from here? I reset the service light once by jumping a connector in there but aside from that have never tinkered with that stuff so will search on here. A bit of searching from my iPhone whilst away seemed to say that warning light can mean any electrical sensor could be out of range, or be caused by an air leak as I suspect in my case.

As an aside, the 850 was the perfect car for long distance winter touring (with new tyres fitted!) in Scotland

Any tips appreciated as ever, cheers :-)

[Stu B]

Just to add, I read the fault codes yesterday after posting and there was only one for A2 jumper setting which was:

232 (Long term fuel trim, idling).

I've reset it now and will hunt for the likely vacuum leak causing it this weekend. If anyone else has had this fault and has any tips they'd be appreciated

[DunkinBiskits]

Get some carb cleaner with a spray straw and blast it in specific areas whilst the car is running. Itll stumble/climb/drop the revs when you spray it in the leaking area. Check inlet manifold gasket, throttle body and gasket, vac tree, PTC valve and seal, inlet pipe between MAF and turbo for cracks in concertina folds, idle control valve air feed and air out, throttle body pivot and ALL boost piping (remove and stretch/flex them as they can seem ok on the outside but have seperated the laminated material on the inside). Also check the one way valve is still working in the EVAP system: it feeds the valve fitted to the rad pack that controls tank vapours, and its worth checking the other end of this line too. It follows the fuel lines under the pedal box and has a rubber push joint that can come out.

Best of luck.
Dunc

[Stu B]

Bit of a thread bump here as I got round to picking up some carb cleaner this week and had an hour tinkering on the car today so see if I could work out if/where an air leak might be. My idle was still regularly settling at just over 1000rpm, and though the car ran well it did sound like it was racing a bit when stopped at traffic lights etc. and reminded me of old manual choke cars when you forgot to shove the choke lever in.

Today I've cleaned out the throttle body and idle valve, checked all vacuum lines, clips and hoses, made sure the throttle cable isn't over tightened, is moving freely and made sure the PTC, vacuum tree and other bits and bobs all appear air tight and correct as much as I can. I can't find any splits or cracks in any of the hoses or pipes, but of course that still doesn't rule out an air leak I haven't yet found.

The revs return to idle perhaps a little smoother than previously and the car is now idling steady at around 900rpm hot or cold on a short test drive. I'll leave it at that for now and see how it goes, but still think the idle sounds a little high (and the rev counter suggests it is from what Dunc says above). I'm keen not to mess with the little screw on the throttle body to adjust the idle until I'm sure nothing else is causing it as I've never tampered with that in my ownership and the car definitely used to idle lower.

Certainly the idle valve seemed to have it's fair share of gunk in, perhaps that'd benefit from a further clean but not sure it'd give these symptoms? When I've worked on similar functions on other cars (Bosch idle stabilisation valve on old k-jet Mk2 Golfs in particular) a gummed up idle valve would give more fluctuation of idle, stalling when you depress the clutch etc. which I don't get here.

Any further advice appreciated (even though I'm sure there is still an air leak I haven't yet found!).

[Luxobarge]

900 is about right for idle on these.

Don't fiddle with the screw on the throttle body, idle is not adjustable, it's controlled by the ECU. The ECU looks for around 900 rpm idle, and sends pulses to the idle air control valve to achieve it. You could clean (or even replace) the idle control valve, but this will NOT be an "adjustment" issue.

[Stu B]

Originally Posted by Luxobarge

900 is about right for idle on these.

Don't fiddle with the screw on the throttle body, idle is not adjustable, it's controlled by the ECU. The ECU looks for around 900 rpm idle, and sends pulses to the idle air control valve to achieve it. You could clean (or even replace) the idle control valve, but this will NOT be an "adjustment" issue.

Thanks, I had a feeling that might be the case and didn't want to adjust that screw really as I'm a fan of not disturbing things like that unless you know exactly what the outcome may be.

I've been out in the car today and throttle response is definitely smoother after cleaning the TB and idle valve, and idle remains at 900 ish rpm. I note that the car will smoothly maintain 30mph in 5th on the flat now, and pickup smoothly off boost from 20mph in 5th (should you want to), whereas it would previously have struggled / hesitated and required a shift down. It's a lovely flexible engine which makes up for it's rampant thirst for fuel somewhat!