My Volvo 480 with a B20F 2-litre engine (same as in Volvo 440, and 460) has been suffering from a slight hiccup at idle revs, for 6 months or so now. My local garage has failed to identify the problem (although I suspect they didn't really try that hard).
Basically, when the revs are very low (between 800RPM and appox 1600RPM), is feels like it misses slightly. The RPM that it misses at varies though - sometime it'll be 800RPM (idle), and sometimes it'll idle fine, but if I rev it slightly to, say 1200RPM, I can feel it missing. Every time it misses, the oil pressure gauge blips slightly too (not sure if this is significant or not).
When travelling along in slow moving traffic, for example, 1st gear, at
1200RPM, I get a kangaroo effect, almost as if power disappears for a split second, and then it has to compensate for it. The same happens in 2nd gear, although the kangaroo-ing feeling isn't quite as obvious, but it's still there.It doesn't seem to make a difference if the engine is cold or not. The ECU diagnostics readout doesn't report any fault codes. I've tried swapping most of the sensors for some from an identical engine I found at the scrapyard. I've also checked the resistance of all the sensors, and they're all within spec. I'm fairly certain the spark is good, and it's not an HT related electrical fault, as there's certainly a good spark at all 4 spark plugs (I found that out the hard way - ouch!).
To try and solve this I've replace: - The HT leads (with Magnecor replacements) - The spark plugs (with Volvo OEM replacements) - The distributor cap - The rotor arm - The fuel filter - The lambda sensor
I've swapped with parts from another car (without making any difference): - The knock sensor - The air temperature sensor - The idle valve - The coil
I've also done an engine oil flush, in case there was a sticking valve.
None of the above have made any difference. Any suggestions where to go from here? The next thing on my list of possibles was that one of the injectors could be playing up. Is this likely? The fault occurred suddenly - it went from being fine one day, to an obvious misfire at idle, the next.
Ben.