hey guys. my car has a slight idle problem. it has been there ever since i put the new motor in. the vac is also low at idle in drive and park but at cruise the vac is great. the car also seems to be using a bit more fuel than i would expect.

so far in trying to solve the problem i have:
- replaced all intake gaskets
- had the mixtures tuned
- replaced the coil and checked ignition components
- double checked valve lash and they are perfect

note the car has heavier valve springs but are just heavy duty crow replacements and is on a straight gas system. anyone have any idea as to why this might be happening. im only getting 300km max out of a tank which is less than i used to and thats 1/2 city 1/2 highway driving. i feared it may be the gas system being gunked up but im not spending anymore money or wasting anymore time without a fair idea of success so any thoughts are appreciated

cheers

I would try a dynamic compression test. That will tell you, without pulling the head if you have worn intake or exhaust seats, a intake or exhaust blockage, etc. I would also double check for any intake/vacuum leaks by spraying WD40 or the like all around.

Dynamic compression check is described here: http://www.imperialclub.com/Repair/Engine/dynamic.htm

Basically it is a normal compression test but you start the engine.

cheers
Scott

Is the gas convertor a genuine Ford unit???? If so, there are 2, 10mm headed plugs, at the bottom of the convertor, remove those and let the oil out. Then refit the plugs with a little pipe sealant..

the convertor is an Impco L convertor and it runs with an Impco 225 mixer. note system is straight gas

any other ideas fellas. i will do a compression test soon but no signs of lost compression so far

The dynamic compression test can tell if you have a blocked cat, blocked intake, etc. Good to try. You could have a bad valve in number 2 intake, say that is causing erratic vacuum. Dynamic will show you this.

cheers
Scott