Whilst cleaning and porting the throttle body a few months back I noticed the inside of the manifold was filthy, caked in oil and muck and resolved to give it clean out which I did about a month ago. I only did the upper manifold as I didn't have the confidence to do the lower one, but whilst it was off I cleaned inside and out and got the flap wheel out and just smoothed it and matched it to the gasket. Once put together it really run sooo much smoother and my mpg went up by 2-4 mpg around town and about 5-6 mpg on a long run.
Easy enough to do.
Three bolts at back supporting the manifold on the block. Take off the inlet hoses, manifold, fuel and brake vacuums.
Remove throttle cable and associated wiring.
Remove spark plugs and holder.
It got me thinking about doing the lower manifold too and maybe cleaning and smoothing the inlet side of the head whilst on the engine. Did it earlier and it was very grimey (175k miles grimey).
Lower manifold involves removing 4 upper bolts accessible one upper is removed OR with long allen keys
Remove four long bolts at the bottom of the manifold.
You can either leave the ISV in place and just remove wiring, but I removed mine and cleaned it out before using sealant when I replaced to ensure it is air tight
Remove fuel lines whilst remembering to use a rag to soak up any spillage as there was slight pressure still in mine.
Also recommend disconnecting the battery too !
Once again I got the flap wheel out and just cleaned and smoother it and matched it to the manifold. I didn't knife edge anything as I just wanted to clean it up a bit. The main thing I noticed was the wires running at the back of the manifold, just about the heatshield was so brittle and the insulation was bare on 4 of the wires and I think they were touching, so I've replaced all of them which should help with some of the rough running and dodgy idling. I recommend you all to check these wires at the back as mine crumbled once started to hold them !
Timewise it took me about an 30 mins to get the top manifold off, another hour cleaning and phaffing.... then the inlet took about 20 mins once I'd worked out there were upper bolts to come out ! I reckon in total about 2 - 2.5 hrs depending on how much time you want to spend on cleaning and smoothing....
Put back together in reverse, check all wiring and pipes and enjoy...
