Carbon buildup...

[Jerry D.]

Anyone know why I would have a buildup of carbon in the air intake chamber and manifold on a high mileage 87 4Runner EFI. The carbon is at least 1/4 inch thick. Just old age???

Engine had a problem with the timing chain cutting into the water jacket and the oil was the typical milkshake. I have not heard the engine running, only the PO says it ran fine with no problems except the water/oil mix. Also all injectors were covered with carbon and looked in bad shape, sent out for rebuild. Found some vacuum lines in/out of the intake that were plugged with carbon, one even had a golf tee (they're good for many things) blocking it off. Not sure how long the engine ran with the water in the oil, but long enough to toast all the bearings and luckily not damage the crank. I haven’t pulled the valves yet, but will in the next day or two. I will be replacing the pistons, rings, bearings, oil pump and or course, timing chain case.

Thanks,
Jerry D.

 

[cruiser88]

It can be many things that is causing the carbon buildup. Likely during the rebuild you will discover it.

Was it throwing a code?

Look at the EGR,O2's vacuum for starters.

 

[Jukelemon]

When I first bought my 92 Truck, the throttle would stick and idle was a bit off. For the sticking throttle, someone mentioned cleaning out the intake/t body. I thought, yeah right....for an EFI??

Sure enough, when I got in there, I spent at least an hour with three tooth brushes and a can of Carb Cleaner getting out all of the carbon/tar that was built up. I am talking a sh-t load.

After that, no throttle sticking (it was the butterfly of course) and steady idle due to a partially clogged idle circuit.