After a good tune up, new plugs, wires, cap, rotor, throttle body clean and aic cleaning the car ran good and idled smooth. Now it still runs good but is idling rough and seems rich at idle. I cleaned the throttle body with out removing it so I may need to remove it and try. I tried a new o2 sensor and it must be bad because it ran rough so I put the old sensor in and it runs ok just idles roughly. Any ideas?
Which of the several dozen models Volvo has produced over the last century is this car? Always post the model and year, it will help people know what to suggest.
sorry it is an 89 740 with 8 valve 4 cylinder and Bosch injection.
You might check your fuel injectors, if they're leaky or clogged they can make it impossible to get the idle smooth. You can pull the fuel rail and injectors without disconnecting the plumbing.
Just handle the assembly gently. The injectors can start leaking at the plastic/metal seam if handled roughly.
Mike
I should add that a few drops of light machine oil at the ends of the injectors can help considerably to lube the O-rings and free the injectors without bending the fuel rail or damaging anything.
Thanks for the input. I tried the wd40 spray on the injectors and no change in engine rpm, before I did the spraying I noticed the check engine light was on. I have not seen this before. I ran the OBD check and got 2 codes both for Lambda sound, o2 sensor I suspect. Checked sensor output and it never changes from about 80 millivolts. Hard to believe the Japanese one I bought on Ebay for 30 bucks was bad out of the box and then the old original with 244,000 miles a short time later goes south. Maybe I should have never touched the o2 sensor. It was running well and I figured hey it can't hurt, they can't last forever. Maybe I need to spring for the almost 200 dollar Bosch unit. They guy said he would send another one when I send this back but now I am spooked by what I believe is a NPK brand, not NGK like the sparkplugs. It had the correct ends and length but the sensor part was smaller.
I'm not referring to the injector seals leaking, but the injectors themselves. When I started my EFI conversion, I had 11 740T injectors. 3 of them were good and matched, one was good but about 5% high in flow, the rest were leaking when closed or WAY off in flow, so it's not unlikely they could use servicing.
Look online, there's instructions for testing O2 sensors out of the car. If it's producing voltage I suspect the sensor is good, a very rich mixture will stick the output at around .80 as well as make the idle rough.
You know, you might check the fuel pressure as well, I recently had the FPR fail on my 740 and it caused all sorts of weird stuff, if it sticks closed the rail pressure will be much higher, causing a higher flow from the injectors and richer mixture.
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