75 V6 fluctuating idle when warm
 

Hi folks,

Having an intermittent issue with our V6. Once the engine is warm, coming to a junction etc when the engine is at idle the revs can vary from around 850rpm to 300 or there abouts, continually going up and down until it cuts out or the throttle is used.

The thermostat had recently been changed but found its opening at around 82°c (not sure if this is likely to cause the issue).
Both breather hoses were replaced as both broke ( the usual one that brakes near the alternator and the other one that is seated next to it when connected to the cam cover).

Can't hear any vacuum type noises from under the bonnet and drives fine otherwise. I've had a read around and believe it maybe down to the throttle position sensor?..

Any advice is welcome
Thanks

Rob

What did they remove when they replaced thermostat?
If they removed the upper inlet plenum, is that seated on the green O rings properly?

Is the flexi hose from the TB to the air box seated correctly?
I’ve seen loads where the rubber underneath is folded so it looks okay from above but massive hole underneath.

You can also buy an Idle Air Control Valve kit, this renews most IACV parts and is a simple easy to do job.

A friend of mine John had a similar issue with V6 erratic tickover and it will cost nothing to try his fix, reset the potentiometer, put ignition in position 2 and press down on the accelerator 10 times, has to be worth a try

I removed the upper inlet manifold when doing the thermostat. I fitted new o rings supplied by dmgrs.

I've tried the throttle reset procedure and it doesn't appear to have worked.

The hose that runs to the throttle body had folded when I was fitting it was a bit of a faff to get it to fit without it folding but it's now fitted without it being folded up.

I've seen the iacv kit that Rimmer bros sell.. may have to buy one then..

I have noticed though that when the revs are all over the place when it should be a steady idle, if I put my foot behind the throttle pedal and pull the throttle pedal up the idle returns to normal and is okay until the throttle is used again.
Thanks
Rob

I shall watch this thread with great interest. When my V6 2.5 is hot, she idles around 900-1000. If I drop her out of gear and coast down a hill, the idle speed often initially 'hunts between 1200 and 1900 revs. Just failed her MOT( rear indicators wrong colour and front anti-roll bar bushes )........yet nothing about emissions which I was expecting. Currently the fuel consumption is slightly higher than the V8 :eek: so I'm glad not to be a road warrior nowadays. I can't hear any vacuum issues either and the hoses all look very good. Nevertheless, contemplating trying a smoke test when I get the chance. Engine has 140k on the odometer. It seems to pull well with no hesitation on acceleration and has never cut out on me.:shrug:

Reference post 3.----If your car has a potentiometer then it sounds like you need to renew it if lifting the throttle pedal cures your tick-over problem.

According to RAVE it's only the MEMS engine management fitted to the 1.8 engine which requires the closed throttle position to be set either by using T4 or by moving the pedal between fully open and closed within ten seconds then waiting twenty seconds without touching anything before switching off the ignition.

RAVE says that the Siemens engine management fitted to the KV6 automatically learns the closed throttle position. It does not give a manual procedure. It's therefore likely that any throttle movement would not affect the ECM but simply clean the carbon track, if you're lucky!

The TPS is indeed a simple potentiometer as Colvert mentioned. I agree that renewing this is a better bet than the IAVC overhaul kit which I have tried with no improvement.

Simon

Is there any free play in the cable at the throttle body?

Thanks for all the valuable information. I'm glad the car learns the throttle position itself. One less thing to worry about hopefully.

I have no slack in the throttle cable at the throttle body end. Prior to removing the upper inlet manifold etc I don't recall there being slack in the cable then either. But the issue wasn't present then before starting work on the thermostat.

I'm going to try and pull the throttle cable out of the housing it sits in at the tb end and see if I can rotate the square block slightly.

What's making me also wonder if it's the TPS is the fact that there was a small amount of oil in the tb and when I had removed the upper inlet manifold I'm wondering if some of the oil has made its way inside the TPS..

Rob

For a 2.0 v6 auto what is the normal idle ?