My wife's frustrating 1993 Volvo 240

The knock sensors can fail, but more likely it just needs to have the connection cleaned and electrical grease applied to protect it. If the new MAF isn't OEM, I'd suspect that still being part of the problem, as well as a yet-to-be-found vacuum leak.

Usually problems like this can be attributed to dirty connections or bad grounds. It would be worthwhile to clean the fuse panel contacts since they are notorious for corroding in 240s, and there's a fuse holder under the hood attached to the inner fender that can be problematic. The sensors themselves rarely fail in my experience.

: > OK, here's the drill. Recurrent check engine lights for most of the : > past year. Lousy, loping cold idle; has had MAF replaced, new vacuum : > hose installed to the dash controls, IIRC a new O2 sensor, crank : > position sensor, new battery, probably some other things I have : > forgotten. I posted about the brake booster a while back as a possible : > source of the terrible idle, which passed all the tests I could find to : > try. The passenger side power windows work sporadically at best (and : > didn't before she bought it). : >

: > Checking the OBD to see why the check engine light is on, I get 1-1-1 on : > socket 2 and 1-4-4 and 1-4-3 on socket 6. Those check out as "missing : > load signal from LH control unit" and "knock sensor signal missing." I : > cleared the codes, we'll see how long they take to come back (and if any : > others appear). : >

: > Any suggestions on further user-performable diagnostics to figure out : > what's going on? : >

: > Thanks! : : : Usually problems like this can be attributed to dirty connections or bad : grounds. It would be worthwhile to clean the fuse panel contacts since : they are notorious for corroding in 240s, and there's a fuse holder : under the hood attached to the inner fender that can be problematic. The : sensors themselves rarely fail in my experience.

Hi Tim,

Further to the excellent advice from James (and I can vouch for the "notorious" bit......), remove the fuses from the fuse panel and clean the fuse panel brass contacts thoroughly by sanding or wire brushing until they are shiny, similarly with the contacts on the fuses themselves; then coat all contacts with dielectric grease before reinstalling the fuses.

Better still, throw out all the fuse panel fuses which have grey-coloured contacts and replace them with same amp-value ceramic fuses with BRASS contacts. This will eliminate the "galvanic action" which takes place between dissimilar metals and causes the loss of continuity.

My local Volvo dealership did not stock these recommended fuses but I found them in (sad to say....) an outfit catering to VW's!!

Good Luck. Andy I. ('58 445 "wagon"; '65 122S wagon; '67 121 2-dr direct import; '74 145 wagon; '74 142; '86 240 wagon; '93 240 "Classic"-model wagon; '97

That's not surprising, nor do I find it particularly sad. VW/Audi/Porsche makes extensive use of Bosch electrics, as does Volvo. Many of the components are similar between the two cars, some are identical.

: > My local Volvo dealership did not stock these recommended fuses but I found : > them in (sad to say....) an outfit catering to VW's!! : >

: >

: : : That's not surprising, nor do I find it particularly sad. : VW/Audi/Porsche makes extensive use of Bosch electrics, as does Volvo. : Many of the components are similar between the two cars, some are identical.

Hi James,

The surprise was not that VW shared Bosch electrics with Volvo, but that VW made a more sensible choice than Volvo concerning ceramic fuses; and I do find that sad.

Andy I.

OK, the recommendations have included:

So, the plan will be to check (or have checked, depending on how much time I have) the electrical connections for the knock sensor, all of the fuses in the driver's door panel and under the hood, replacing fuses with aluminum contacts, and locating that pesky as-yet-elusive vacuum leak.

I do think there is still a vacuum leak somewhere. I really thought it was likely the brake booster- given the rhythmic quality of the "surge and falter" at idle I figured that the volume of the brake booster made it the best candidate. And maybe the vacuum leak is temperature dependent since it seems to only happen well below freezing- something has to shrink enough in the cold to leak.

Thanks!

You can plug or pinch off the hose to the brake booster to verify that, if kinking the hose changes the way the engine runs then there is a leak. Check the flexible air pipe between the air mass meter and intake manifold too, sometimes the accordion pleats split and that will give you a huge vacuum leak. I've also seen an intake manifold gasket damaged by excessively vigorous pressure-washing that caused poor running.

Thanks, I'll check for those too.