Hello. First post. I have a 1981 Volvo GL B21F K-jet NA with an IPD VX cam and adjustable cam timing gear. 500K miles. It's been a hangar queen for the last 6 months because of a hard-to-start issue. I've done a ton of work on it. The fuel pressures (by CIS gauge) are all within Volvo specs, and the fuel flow is good. The fuel filter is new, the pressure plate is adjusted and seems to work correctly, the air-fuel distributor is cleaned, the valves are adjusted, injector seals and holders are new, most all of the vacuum hoses have been replaced. The charcoal canister is bypassed, and the cold enrichment part of the CPR is open (my ported vacuum switch is broken and I can't find another one). I installed a Volvo pulse relay for the cold start injector. O2 sensor connected or not seems to make no difference. The boot is tight and the intake manifold gasket is new. All of the flame trap parts (including the oil trap) are new. Before this last round of work I did a compression test and all 4 cylinders were within spec.

None of these things seem to have had an effect, except that now I can't get an idle below about 1200 rpm. I've had to adjust the little screw on the throttle linkage just about all the way in, which means the micro switch on the Constant Idle System never engages. I've attached a vacuum gauge to the manifold on the front port (where the vacuum line to the ported vacuum switch would normally go). When I crank the engine the vacuum needle barely moves. It swings a little in concert with the engine cranking, but it doesn't seem to do much more than a couple or 3 inches of vacuum. When the engine finally starts (which is usually accompanied by much gas pedal pushing) the vacuum gauge will eventually get to maybe 16 inches at around 2K rpm. Sometimes I need to take it to 3K to get the vacuum to settle down to a steady reading. Occasionally I can get it to sit at around 1500 rpm and just run for a while, but usually I have to stay on it with the gas pedal to keep the engine running. If the engine speed drops to around 1100 the vacuum drops to around 6 inches and the engine will start to sputter, while the vacuum gauge goes crazy at the low end. Sometimes I can catch it by pumping the gas pedal but usually the engine just dies. Trying to re-start it is harder after that.

I've done a lot of manual movement of the pressure plate. With no control pressure present the plate is easy to lift with no restrictions, and does the little bounce thing when I let it go. With the fuel pumps running it is harder to lift but it doesn't have to go very far to get the injectors to spray. When I crank the engine with the injectors out and the holes plugged, I'm lucky to get a few spurts of gas out of them, but the cold start injector seems to work fine.

Right now I'm thinking this is a vacuum issue. I haven't been able to find what the normal "cranking vacuum" spec is, but it's hard for me to think that just a few inches is enough to push up that pressure plate, especially when the warm control pressure has kicked in.

Thanks in advance for any words of wisdom that could help me.