Idling - Throttle Body

[v6Max 0]

I've had a tricky problem with the idling on my car; everything works fine until it's driven at which point it will randomly idle at 1000rpm or 1500rpm and various speeds in between.

 

Anyway, the problem looked like it was the TPS - when it was idling high tapping the TPS or waggling the wires to it seemed to get the idle to drop down to the normal.

 

Having replaced the TPS (for the not so bargain price of £75) the problem still occured and finally I was able to get it to exhibit the problem on the drive way. Turns out that following large throttle movements the throttle is not closing properly. The stop screw is set correctly but if you twist the thottle cable cam the revs return to normal idle - so it looks like the throttle body is worn. It looks like there is wear in the throttle spindle allowing it to stick slightly open and therefore raise the revs.

 

I have taken the thottle body off the car, cleaned it completely, reset everything as per the Haynes guidelines, metered the TPS so I know that is one hundred percent working.

 

Now finally getting to the point; is there a way of reconditioning the throttle body or is it time to surf eBay to find another one? Has anyone seen this before and knows of a fix?

 

Thanks

[welshpug 1,657]

Sounds like you may have the TPS set too close to the throttle spindle's rest position, try setting it a touch further.

[v6Max 0]

I've done that, unfortunately. It's definitely only a problem when the throttle is opened and then closed if you see what I mean. It's as if the throttle butterfly is flexing so it's staying open just enough to increase the revs - a twist of the spindle will close it again but crucially it's not consistent which I'd expect it to be if the TPS was holding the spindle open.

 

To set the position I slackened the TPS right off, set the stop screw to + four turns after blade contact and then used feeler guages to get the closed/open positions correct before tightening up the TPS so I'm pretty certain that it is set right.

 

The throttle stop is definitely being hit even when the car is holding high idle which is why I suspect it's wear or "slop" in the spindle bushes.

[lagonda 42]

Hi,

 

Can't say I've got experience of this problem, but I'd certainly say your theory sounds correct. Wear in the throttle spindle would allow unmetered air in under certain temperatures/positions.

 

Way to check would be to squirt some Redex around each side where the spindle enters the throttle body, whilst you have your high rev idle scenario. If the diagnosis is correct, the Redex will be sucked in, either reverting you temporarily to low idle, or give you the odd puff of white smoke out the exhaust. In either case you should see the Redex being sucked in.

 

I know you can get throttle bearings re-bushed with new spindles for carburettors for old cars, so rebuild should certainly be viable, although you may be able to buy good secondhand cheaper. If you get rebuilt, obviously important everything done accurately!

 

Good luck.

[v6Max 0]

I checked this lunch time to see if it was the TPS and unfortunately it wasn't!

 

However twisting the throttle cable cam bit (the bit made of plastic) side to side rather than up or down allowed me to recreate the problem easily so it does look like this is the source of the problem.

 

I'll take a look again tomorrow and try Redex/Carb Cleaner etc and see if it's a leak of if the throttle is twisting and staying slightly open.

[jackherer 543]

Is this an 8V you're talking about? Mi16 throttle bodies are known to wear in such a way as to let extra air pass the throttle at idle, its still metered by the AFM but the ECU is ignoring the AFM as the throttle switch says the throttle is shut.

 

Who on earth charged you £75 for a TPS? Is that the dealer price? Its shocking whoever it was

[v6Max 0]

Sorry, yes it's an 8v - £75 was main dealer price, they were "surprised" as well at the price. It also took sometime for them to get hold of. To be fair the original one was definitely not always consistently closing properly - at least that's what my meter showed.