'91 refuses to keep running when engine is warm
 

I've got a 740 that is running really inconsistently, refusing to keep running when it's warm, really low idle. What might I check or do to rectify this problem? Thanks in advance!...

check the coolant temp sensor? check the idle air controller?

any codes on the OBD-I diag block?

Idle Control Valve, most likely... You can take it out, clean it, make sure it's not stuck and it operates smoothly.
"The fumes from the breather are carrying oil and combustion vapors. When this stuff attempts to past the butterfly in the mostly closed state, the pressure (and hence temperature) drop causes the fumes to condense out of the air stream... sticking to the walls of the throttle housing right around the butterfly... a petroleum snow storm. As an aside, this buildup can cause really weird problems on cars with automatic IACs (idle air control: idle speed control). The gunk will restrict the air flow through the butterfly, forcing the IAC to open farther to maintain a proper idle speed. On some cars, you end up with the IAC operating well outside it's designed range... resulting in a major ring/hunt.Do NOT adjust the throttle stop! Clean the gunk out.

Guys, this is a friends car, so I may need a little more help than usual since I'm not familiar with the setup. Are there any diagrams available showing the Idle Control Valve, so I know what to look for when I do this "fix"?

If not, even a description of where it's at, and what to look for, will help...I'm pretty mechanically inclined.

I'm guessing the butterfly is inside the throttle housing, correct? Len, what do you suggest I use to clean the gunk out???...

throttle body/carb cleaner spray to clean the throttle and the idle air valve. said idle air valve is under the intake manifold, and has two short hoses that connect it to either side of the throttle body. the idle air valve has an electrical connection, the ECU sends it pulses to open/close it to control how much air it lets in to maintain a steady idle speed.

labeld 'IAC' here,
http://www.threefattigers.com/Protoc...230Fb_2436.JPG

Pierce, thanks for the photo. I've passed the information along...looks like an easy fix!

My friend is still having problems with her car. She sent out her computer/ecu for testing and it was fine. Last weekend she changed-out the fuel pressure regulator, but that didn't fix the problem and she now has no running car. Any other suggestions?...

what year 740 is this? there's 3 possible different setups for the fuel injection, Bocsh LH 2.2 (pre 1989 only), Bosch LH 2.4 (1989+ non-turbo or 1990+ turbo), and then there's Regina systems, which I'm MUCH less familiar with. Both Bosch systems have a Bosch 'mass airflow meter' (MAF aka AMM) in the intake air path between the air filter box and the throttle body. The regina systems have instead a 'MAP' (manifold air pressure) sensor, which is more anonymous looking than a MAF. Regina systems also use different ignition systems, with a square ignition coil that has an integrated power module. The Bosch LH2.4 systems use a Bosch EZK ignition control unit with a seperate power module, and round coil, while the LH2.2 uses ? ignition control and hte same round coil.. The LH2.4 cars use a 'crank position sensor' for timing, while the LH2.2 cars have a hall sensor in the distributor.

in a no-start, the first thing to do is determine, is the engine getting fuel? is it getting spark? does it have compression? takes all 3 to make it go.

1981 through 1987 Volvos suffer from 'biodegradable wiring', and frequently have insulation failures under the black tubing around hte harnesses. this can make for all sorts of random hard to diagnose problems, and the only real fix is acquiring a compatible harness made after 1988, or completely rewiring the engine, which is a massive undertaking.

I assume it is a '91 as that's what the title of the thread states. Have you checked for engine codes as Pierce originally asked? That would be a good starting point. Other things to check are fuel pump. Do you hear it run for a second when the key is turned to the II position? If not, then chase down that problem. Other item to check is the crank position sensor. It is located on the top of the bell housing where the engine and transmission meet and has a fat black coax wire running to a connector on the firewall. Check this wire for flaking or fraying insulation. If the insulation is cracked & flaking, then it needs replacement.