I have read some of the postings for similar Volvo issues and realize that this may be caused by several things including a failing Crank/RPM sensor or fuel pump relay and I will replace them if necessary. I could also replace the cold start valve. However, I would appreciate any comments from those experienced with the 940 Turbo fuel system.

The symptoms of rough idle at a cold start began shortly after I had the radiator replaced when it had the well-known catastrophic failure. I was careful to have the car towed to be repaired. (Don't know if this has anything to do with it.)

Took it to my mechanic who replaced the plugs, cleaned the intake manifold, and replaced the plug wires. This seemed to help for a while but the symptoms are back! I added fuel injector cleaner which I commonly do every 4 or 5 tankfuls. Any further suggestions for repair would be much appreciated. I do minor repairs myself but also like to know what is going on before I take it to my mechanic!

Dear rlstites,

Good p.m. and may this find you well. The ECT - engine coolant temperature sensor - mounted in the head, below the intake manifold arms. towards the rear (driver's side, USA/Canada models) may have been damaged, when the car over-heated.

It may be sending the Engine Control Unit (ECU) a signal, that the coolant is "cold", after the coolant has warmed (or vice-versa). As a result of this erroneous signal, the fuel/air mix is too rich (which might account for the smell of gas) or lean (too little fuel). Typically, though, this signal will be consistent.

Another possibility, which should be checked first: a Dirty Idle Air Control Valve (on bracket below/beside the intake manifold, driver's side of the engine bay). See the FAQs, under FEATURES, above, for instructions on cleaning it.

Because changing the ECT is time-consuming, start with cleaning the IACV. Then, check the RPM sensor. If it is the original (it likely will have a yellow painted marking around the harness circumference, at some point; later units have a white band), it should be replaced. The insulation becomes brittle, allowing moisture to get in, which causes shorts. When the signal is lost, the fuel pump shuts down. That, plainly, could cause the engine to run "rough".

Hope this helps. Post back, with your findings.

Yours faithfully,

spook

I spoke too quickly! Seems like the Idle Air Control Valve either did not get cleaned enough or it is faulty! It worked well for several days but is now about only 50% better than before I cleaned it.

Question: They are asking $50 in my area now for the used IACV and I can get it new for $160. I am supposing that I should buy the new one, since the salvaged model is tested only electronically and I would hate to have to take it out again if it did not work or only worked for a year or two! I plan to keep the car at least another 5 years so it is worth it as long as the new Bosch IACVs are the same quality as the original ones.

Any experience or comments from anyone concerning this choice?

Robert