Empaneling yee higher authority on my tune uppe

[Caleb]

Your honors,

My 2001 xc70 turbo (155K) is doing a typical thing in an untypical way. I've been on the case for two weeks with limited results. Primary symptom is alternately starting fine and driving well THEN next start up, surging, missing and barely drivable WITH NO BRAKE VACUUM. Then turn off- turn back on and she'll run fine again. Maybe 10 starts bad, 1 good. Followed by 20 good and then 1 bad. But then maybe 30 bad starts in a row. Real problem.

So I changed plugs with OEM Champion and put 4 new volvo coil packs in, new fuel filter, removed VVT solenoid- was not engaging, cleaned and got it working. Gasket gone, very varnished up. Installed new gasket. Should I get back in there and check the little ports for clogs?

What I don'tt understand is the randomness of it all, coupled with losing brake boost. I don't believe in intermittent vacuum leaks bc the brakes work fine on a "good" start up. I cleaned my MAF (with alcohol). If I unplug it, car stalls immediately.

CEM under driver side dash is perfectly clean. I removed every fuse and module in the car (all three locations) and scotch brite cleaned connections. Also did this with CEM.

Back story is that Ive had to drive thru some deep puddles (New Orleans) and gradually my dash lights began dimming and then cut out. The headlights even randomly stopped working- I had to hold the highbeam lever IN and drive that way!

But since replacing coils the dash is bright and headlights work normally. What I can't figure out is losing break boost when on a "bad" start.

Error codes are P0121 throttle pedal position sensor A
P0171 too lean bank 1
P0014 B camshaft position over advanced

I don't know what to try next. PVC is not bad, it won't inflate a blue glove. The PVC hose that comes up under intake manifold and clamps up by the oil fill leaks a bit so there is some fresh oil under the manifold. I think I can reach under when the engines cold and get that hose off in case it's blocked- but if its blocked it's blocked - not on one start cycle and not the next!

I'm suspecting wiring, I've replaced the engine ground to firewall. Are there other grounds I can check/replace? I jiggle and massage the wiring while it's running and not getting any performance changes.

The Jury is out - any one ever solve this one? I don't understand intermittent good car / bad car stuff. Let alone good brakes / no brakes.

[Georgeandkira]

With it running well have you tried flexing the vacuum booster line (thick hose)? It or the fitting at the booster can be cracked.
There are brake boosteer vacuum lines (hoses) ahead of the air cleaner box too. Check those.

I do not know if intermittent brake failure is a symptom of a failed booster. It'd sure be convenient if it was.
Also on our brakes have been reported failure due to scratches (scoring) of the white plastic piston / plunger visible from inside the car. There's a seal which goes and a suitable (teflon friendly?) lube available. I don't believe the lube fixes scratched pistons.
Fortunately for me and my '07 the seal is redesigned and feels like it bathes my plastic piston in juice. Others are bare and vulnerable.

You also could have one of the original "bad design" MM throttle positioning mylar wipers. They wear out and your year and mileage line up with those stars.