1990 740 hesitation
 

my 1990 740 has developed an odd hesitation. It usually only occurs when taking off from a complete stop, acts like it is running out of gas. It also has a hard time starting when cold. It started about 3 months ago and nothing I have done has improved it. I have changed the dist. cap and rotor, plugs, plug wires, fuel filter, half the vacuum lines and checked for vacuum leaks with carb cleaner. When it is cold it just cranks and no fire. Stop for a second and try again and it starts right up.

Any thoughts?

When it hesitates from a start, are you easing into the throttle or are you accelerating briskly? When you get up to speed and wish to accelerate, does it do it then or just from a standing start? Do you have the Rex Regina ignition or the Bosh LH2.4? Easy way to tell is the Bosch has a normal cylindrical coil while Regina has a square looking coil.
Just to throw some ideas out there: If it's Regina, could be the MAP sensor. For either system, the crank sensor dying slowly can cause all sorts of quirks. There is a fuel check valve under the car near the fuel filter that is designed to keep the car's fuel line pressurized to make cold starts faster...could be bad. Also, there was a TSB for modifying the cold start injector. Seems they have a bad habit of running too long when controlled by the ecu. Volvo recommends it be rewired to only run when the starter is energized to make starting easier. It could very well be that the two symptoms are unrelated. The stumbling could be a dirty throttle body butterfly and the hard starting could be a bad check valve for instance. You'll need to drag out the trusty multi-meter and check voltage on some of these sensors to see what's out of range.

It hesitates from the start if I am stepping on it or if I am at higher speeds but at low rpms and step on it. If I step on it hard and it downshifts (auto trans), increasing rpms, it takes right off.

I have a Regina ignition, checked vacuum lines, they seem in good condition with no leaks. I believe the two problems are connected as they started at the same time. Using a liquid fuel injection cleaner in the gas helped some, but not cured the symptoms. Where is the crank sensor and should the voltage ranege be across the MAP and cranks sensors?

Thanks for the help and thanks for the reply on the 240 heater fan, I'll give it a shot, it's about the only 240 repair I have never had the pleasure of.

My 1990 turbo has LH 2.4 and a new O2 sensor eliminated the dead spot off the line under heavy throttle. I think it's the car momentarily going dead lean before the computer figures it out. I think, being so adaptive, the computer gets used to the car idling and relies heavily on the o2 sensor to maintain a nice mixture, thus catching it off guard with too lean a mix, probably the AAV open too far.

Regards, Andrew.