Odd idle problem

[diggerdave]

My 1KZ-TE with 182,000m idles fine in normal circumstances (although it can vary between 750 and 850rpm (always steady) depending on how hot/cold it is, which I don't see as a problem).

From time-to-time, only when in slow-moving traffic after a longish (1hr+) journey, the idle drops right down to around 400 to 500rpm when changing down the gears . It's only for a few moments but it almost stalls. I can't reproduce it when stationary, it seems to require the engine to be under load before dropping the clutch ready to change down. It never has stalled, but the whole car shakes as if its about to.

I thought I had cured it when the problem first happened a few months back by a combination of changing the fuel filter and disabling the EGR, but now the problem is back and I wonder if I really 'cured' it at all.

Altering the idle speed using the tiny screw on the throttle body doesn't have any effect on the problem.

The car uses no oil or water and starts and drives perfectly, engine serviced religiously every 4-5000m for the last 30,000m

Could this be a TPS issue? Fuel supply? A dodgy tank of diesel (I did fill up at a non-branded petrol station)?

Any ideas appreciated, please!

 

[Shayne]

Forgive me for asking but are you not leaving it too late to change down , mine shudders like an old bus when i when i accelerate in 4th when i really should be in 2nd .

 

[diggerdave]

Cheers Shayne, but no, it's not when the clutch is engaged. It's when you disengage the clutch and coast for a second - usually while braking - before selecting the next gear down and raising the clutch pedal again (e.g when approching a roundabout or in an irregularly moveing traffic queue - you might just coast briefly while deciding whether to change down to to 3rd or 2nd for example).

Normally in that moment the revs would drop to 750rpm ish, whereas mine drop to 400rpm and the engine nearly stalls... If I hang on and wait (traffic permitting) before engaging the clutch they will slowly climb back to 750ish over a couple of seconds.

 

[Shayne]

Beau is better at this kind of stuff but my thinking is you have a leak in the fuel line somewhere and a none return valve after the filter might be the answer .

Guesswork guesswork wait for Beau to reply .

 

[diggerdave]

I might have been on to something when I mentioned dodgy fuel,

I changed the air filter last night with no effect. The idle was rotten this morning on the way to work

But I topped up my half-full tank from a different petrol station and no issues at all this afternoon

Fingers crossed that's all it was... phew!