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1998 V70R occasional misfire (P0300)

Help, Advice and DIY Tutorials on Volvo's extremely popular car line -- Volvo's 1990s "bread and butter" cars -- powered by the ubiquitous and durable Volvo inline 5-cylinder engine.

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1998 V70R occasional misfire (P0300)

Post by uyvolvo » Wed Dec 12, 2018 5:01 pm


I have a random misfiring at idle that is driving me and mechanic nuts. Details:

1998 V70 R, 165 K
Symptoms: car will start fine, run for a while and then occasionally misfire at idle or at stop-lights. Throws a P0300 code. Tachometer stays steady at 1000 RPM and car will usually run well after these misfirings It also runs well at higher speeds.
Did a full tune up (cap/rotor/spark-plugs/wires), changed crankshaft position sensor, knock sensor, coil. Nothing helps.
Mechanic thinks that it may be a weak valve spring and suggests doing the heads ($$) but I am not convinced, since I thought that a weak spring will lead to poor running at higher rpms, not idle.

Any suggestions / help greatly appreciated.

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Re: 1998 V70R occasional misfire (P0300)

Post by WhatAmIDoing » Wed Dec 12, 2018 5:24 pm

Grab a new Volvo fuel pump relay. I had a KAE relay cause random misfires at idle as it began to fail (didn't realize it was the relay until after I did new plugs, wires, cap, & rotor). Consider changing the fuel filter as well if you have no idea when it was changed.

You should look for vacuum leaks. Your idle should be closer to 800 RPM, not 1000.
'98 S70 T5M - 276,000+mi - forever a project
'99 S70 "AWD" - 220,000+mi - wrecked :cry:
Knows enough to be dangerous :wink:

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Re: 1998 V70R occasional misfire (P0300)

Post by misha » Thu Dec 13, 2018 4:36 pm

Check gap on those new spark plug(if they are not Volvo plugs),since it's critical for turbo engines.
'97 850 2.5 20v / fully equipped / Motronic 4.4 from the factory / upgraded with S,V,C,XC70 instrument cluster / polar white wagon
'91 Citroen XM 2.0 SI /fully equipped/mandarine red metallic
History of Volvos in the family:
'71 144 S
'73 144 De Luxe
'78 244 DL
'78 244 DL
'79 244 GLE
'85 340 GLS

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Re: 1998 V70R occasional misfire (P0300)

Post by scot850 » Thu Dec 13, 2018 5:24 pm

We say it time and time again that the parts used can determine issues you may get. Can you state the brands of the parts you fitted as some brands are known to be incompatible with these turbo motors.

2000 V70 R - still being an endless PITA
2006 XC70
2003 Toyota 4Runner V8 Limited
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Re: 1998 V70R occasional misfire (P0300)

Post by erikv11 » Thu Dec 13, 2018 5:35 pm

Agreed, super important: replaced ignition components with what brands of parts?

And I like the fuel pump relay idea as one possibility, and note that if the misfires are consistent you can test it with a jumper wire before you shell out the $45 for a genuine Volvo relay.
'95 854 T5-R, Motronic 4.4, 185k
'96 855 NA, 145k
'98 S70 NA, 220k (living out west)
'98 V70, T5 tune-injectors-turbo, LPT engine, 285k
'06 S60 R, 165k
'99 Camry V6 :shock: 125k
gone: '96 NA 850 210k, '98 NA V70 182k

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