D4d Lumpy Idle Cured

[BobHT]

Many thanks to all those who advised me. Its cured now.

Symptoms: Lumpy tickover when cold, it sort of hunts up and down and feels like its going to stall. When warm just slightly lumpy tickover.

Cure: When looking at the engine from the front of the car, on the left there is a shiny bronze vaccuum advance/!Removed! thing at the front of the engine. This is connected to a casting that is held to the front of the engine by four 12mm bolts. This same casting also holds the dipstick securing plate and part of the wiring loom (with 10mm bolts). It has a 2 inch diamater short hose going to its top from the air cooler that sits on top of the engine.

ONE Undo and remove the hose from the air cooler - may need to loosten the air cooler first (I did).

TWO Undo the 10mm bolts that hold the dipstick and the wiring loom to the casting.

THREE Undo all the 12mm bolts. You are dealing with aluminium, so undo all bolts a bit at a time to avoid distorting anything (same applies when re-fitting)

FOUR Take off the casting.

Look in the casting - mine was really full of carbon so that an internal air-way was virtually blocked. Clean all this crap out anyway you like.

Also, clean out any carbon in the manifold - i.e. look into the engine block and clean out the crud you can reach with a rag.

Re-build it all, then marvel at your tickover returning to its as-new sound. Nice.

Splendid. Hopefully that'll last another 40,000 / 50,000 miles or so.

It took about an hour and a half.

Cheers all and good luck. Back to smooth motoring and 70 mpg.

Bob

[dustyhog]

Thanks,

Mine had same problems and your post was spot on - Tried recon MAF but your solution sorted it. Completely jammed up with black crud.

Mine only had 30,000 miles so amazed a part could be that jammed.

Anyway thanks.

[Johnaa]

Thanks,

Mine had same problems and your post was spot on - Tried recon MAF but your solution sorted it. Completely jammed up with black crud.

Mine only had 30,000 miles so amazed a part could be that jammed.

Anyway thanks.

Hi, I am overyjoyed. I too have been struggling with this problem for 6 months and despite several postings nobody came up with an answer till I found this. Many thanks to bobHT and dustyhog for bothering to post the solution once they had overcome the problem. Incidentally my Yaris D4D only had about 20,000 miles on it when this problem started up. When I took the EGR assembly off this weekend the 'bypass' hole at the bottom was pretty well completely blocked. I find myself wondering if this is caused by using 'cheaper' Tesco/Sainsbury diesel or would it have happened anyway.

[RichardM20]

Hi, this worked for me too. About a year ago my wife's 2004 diesel D4D Yaris started revving erratically when idling and gradually it got worse to the point where the revs were jerky even when driving reasonably fast. When I took off the manifold as described above, I found that the passage for the exhaust gas to merge with the intake air was completely blocked by black gunge that looked like Carbon. I cleaned it and the engine is revving perfectly now. It's got 85000 miles on it, mostly city driving. A garage had tried to fix the problem twice but failed through they did notice that the baffle on the air intake manifold was unstable. This baffle is just above the hole which admits the recycled exhaust gas. If they had looked a bit deeper they might have discovered the blocked hole. Bizarrely, after each attempt by the garage, the engine revs hunted less for a few days. Maybe they reset the mapping which might have improved the rev control temporarily. The engine diagnostics didn't show any error although judging by internet search results, some cars can detect blocking of the exhaust gas recycling.