Hello all.

Still the original owner of this 1983 240DL. Manual trans, no turbo, LH2 Jet, non-white distributor cap (but I think MPG ignition none-the-less). Well over 200K miles but odometer broke at 190K and I haven't bothered to fix it.

The car was idling slow and poorly, ran ok but not great when in motion, stinky gas smell out of the exhaust all the time. Took it to a local mechanic who discovered that part of the intake manifold gasket at #1 was missing. He showed me and I could see it was missing. He said he shot some spay in there and the idle changed. So I just had that replaced. I can now see the entire gasket and it looks fine. But the engine still runs like crap.

So I reviewed my old Volvo Problem Solver book and video. Today I started to see what I could see:

(1) Checked the timing belt tension. Belt was replaced in 2015. Loosened and re-tourqued to spec. No changes.

(2) Pulled the plugs which had been put in by the same mechanic when originally trying to "fix" the problem. He also replaced cap and rotor. Anyhow, all 4 plugs were black with soot (as I would expect) but had gaps were all less than .5mm. I brushed clean and re-gapped to .7mm. No change.

(3) Checked for and heard the click from the throttle micro switch. Did not have to move things much for this to happen.

(4) Tried to set "base idle" which Problem Solver says is done by grounding the blue/white test lead on the left side of the engine. Supposedly, this disables the constant idle system. Once grounded, should be able to set an idle speed of 750 rpm using the thumbscrew on the throttle housing. In my case, grounding the test point causes the engine to be VERY HARD to start and wouldn't stay running. Removing the ground allowed the engine to run poorly as before. I turned the thumbscrew all the way in and out and see no difference whatsoever in idle speed. Stays low at 700 or less.

(5) Tried to adjust mixture screw on AMM. Problem Solver says to measure voltage at the pink test point wire on the left side of the engine and it should vary between 0 and 3.5 volts. Turning screw clockwise should richen, reverse to lean. In my case, the voltage stayed at .1 (very rich) and nothing would make it change at all.

(6) Tried to test the O2 sensor. Problem Solver says it should output varying between .3 and .7 volts. Before starting the engine (but after it had been recently run), I get .6 volts. With the engine running I get .8 to .9 volts (rich). Grounding the wire going from O2 sensor to controller should, Problem Solver says, send a false lean signal and the controller should respond and we should see that with a higher voltage on the O2 sensor. Grabbing that same wire while touching the positive battery terminal is supposed to send a false rich signal and the controller should respond and we should see that with a lower voltage on the O2 sensor. In my case, nothing changed the O2 sensor output at all (or anything else for that matter).

(7) I also tried removing the AMM connector (all power off when doing this) and maybe the engine seemed a little better - slightly smoother idle. But still no real changes.

So now everything is back together and nothing has changed. I figure all the easy stuff is done and don't know at all how to interpret the results or how to proceed.

Any suggestions will be appreciated. Thanks!