I have a 1973 145 wagon that had the low compression F head in it. Wanting to upgrade, I installed an F head that had been milled down to E head specs. I'm not very knowledgeable on rebuilding, and never knew, until I read an earlier post on rebuilding the B20, that the surface of the head had been hardened. Sometime after I installed the "E" head, I began to experience an erratic idle(this car has the D-Jetronic system on it, not carburetor). At cold start the car would idle at around 1000, as it should, then cut back to 750 as it should, but then sometime soon after it warmed up, the idle would suddenly drop to around 150, barely able to sustain itself. Go into a store, shop around a bit, come back out, start it, idle would be back up to 750. But a few minutes later it might drop back down to 150. And so it would go. I tore my hair on that injection system, replacing absolutely everything, from the pressure regulator to the temp sensor to a rebuilt distributor, but nothing has ever cured that erratic idle to date. The shop that did the milling on the head ripped me off, putting in valves they said would handle unleaded gas (they didn't, they seized, but fortunately came unstuck and thereafter I added a lead additive), milled out a divider between the intake and exhaust valves, saying it would up the horsepower, etc. I'm thinking of restoring this car back to specs, but I would like to know if the milled head and the erratic idle are connected in some way, i.e. warping or whatever. Any possible explanations from anybody on this site would be most appreciated. Dick