I have an '84 240 dl wagon, and I think I have a relativley unique problem. I have a rpm and enine spike during idle and while accelerating. When the rpms spike (usually from 2000 to about 5000 at the highest), the engine never really reaches what the rpms read. So this tells me that it's an electrical problem. Now, sometimes the idle spiking goes away, but the acceleration spike never does. I have tested and cleaned the air control valve, the tps, and the connections to the icm, tested for continuity on the supply circuit to the coil, and checked all grounds. The only time something seems to change is when I mess with the icm. From what I understand so far, the icm either works, or it doesn't. What I don't understand is why this is so difficult to find on a relativley simple set of circuits..... Could someone perhaps point me in the right direction, or give me something else to look for?

Well, after several more tests and the frustration only a mechanic can understand, I have managed to find the culprit. In the icm wiring harness at the cannon plug, there was a tiny little break on the underside of the supply wire leading to the ignition advance. It was enough resistance to cause little surges which caused very large differences in the timing that caused the car to lurch. So I just pulled the wire out of the cannon plug, and soldered it back in and wrapped it in heat shrink. Problem fixed, and it's a very smooth ride again.

Does it sound like it spikes. Could be your tach has gone. Just a thought. Sounds like a signal issue. How long does it spike.

it's not the tach. the engine actually tries to rev up as well, but it doesn't have enough time to peak before the tach goes back down. and it does it very quickly a whole bunch of times. From what I can tell, is that whatever is telling the distibutor/coil to fire is what is screwing up the steady speed the engine should be running at.