My 86 740Turbo will not idle or run at low power once it has warmed up. When first started, the engine runs fine and has no trouble idling. After a few minutes, however, problems begin to develop. When run at higher speed or under load, the engine seemingly develops normal power but staggers and threatens to stall when allowed to return to a 'neutral power' condition. When the warm engine is allowed to idle for more than 15 or 20 seconds, it begins to stagger as if it was getting too much fuel and then stalls. Immediate re-starting is difficult and, once achieved, the engine must be 'babied' up to a higher RPM before it begins to run normally.

To begin the repair process, I first bought and installed a new engine wiring harness, as the original was exhibiting all of the typical problems of deteriorated inslulation. In the process of replacing the harness, I checked and cleaned most of the intake manifold and hoses, confirmed the operability of the constant idle valve (motor), checked the fuel injectors for leakage and went over the remaining wiring harness looking for obvious problems. (I have also hopefully fixed a major oil leak by replacing the front shaft seals, replacing the timing belt as well while the front of the engine was exposed.)

While I harboured a forlorn hope that the problem would be resolved by replacing the wiring harness, that has not proved to be. I have now begun trying to evaluate the performance various sensors (and have ordered shop manuals from Volvo to aid in this endevour) but so far I have made no obvious discoveries. I have reviewed some of the archives on the Brickboard but did not see anything that was similar to this problem.

My history with Volvos goes to 1973 when I bought a 1971 142e (which I still own and is temporarly off the road waiting for me to re-weld the suspension to the body), a 1973 142 parts car, a 1982 240GL wagon which is currently being used to substitute for the 740 and, of course, the 740 itself. My background is in electronics and mechanical devices (I work for the local power utility) and I own or have access to a relatively wide range of test instruments so troubleshooting has normally not been a problem.

If anyone has had similar problems or can suggest a rational for troubleshooting, both I and my son (who normally drives the 740 and has been forced to used the rusty old wagon) will be very grateful

Thanks

Gary