This is driving me nuts.... 1999 Legacy Brighton wagon, 2.2 phase II, 5MT. Around 160k. It has developed an intermittent dead spot on the throttle -- it idles fine and does not stall, and if you floor it, it pulls very nicesly -- but it in between, it will just cut out when you are driving, then cut back in if you push the accelerator farther down... let it up a little, and it cuts out again. It jerks the whole car when it's doing this (whiplash anyone?

 

Sometimes it doesn't do it at all.... (usually when I'm doing a test drive to try to figure it out...) and sometimes it seems like it only has off and floored as options... which is really obnoxious driving on flatter roads where it doesn't need to be floored.

 

So far.... I've replaced the TPS, and cleaned the MAF -- that seemed to help for a few days, then it was back. It's been doing it for about a year now, and getting progressively worse. It seems to be worse when it's first started, and better after an hour or two of driving (we did a 3,000 mile trip in it recently). I haven't replaced the fuel filter, but it's not acting like a bad filter, because it runs fine when you floor it, but not in between. I'd expect a bad filter to be worst under the highest throttle (or at least when I've had them before, they behave that way)

 

Got any ideas? I'm going to try to get a used MAF and try that... but other than that, I'm stumped.

TRIPLE check that big - 1" or so - hose from the IACV to the underside of the intake.

 

any CEL codes stored?

 

How old are the plugs and plug wires?

TRIPLE check that big - 1" or so - hose from the IACV to the underside of the intake.

 

any CEL codes stored?

 

How old are the plugs and plug wires?

 

I'll check the big vacuum hose again...

 

There is a CEL, but this started happening before that... I'll pull the codes (I'm pretty certain it's a rear O2 sensor code)

 

Good question on the plugs and wires... I thought I replaced them about a year and a half ago, but that might have been a different suby now that I think about it (the problem with having several....)

Just an idea because once I had a similar problem. You could have a baffle loose inside the muffler flopping around restricting exhaust flow.

I had the same thing happen to my 99 brighton wagon (a/t). look up my past threads. Don't even have a MAF sensor (don't ask unless really interested). Occasional codes thrown. It seemed temperamental with the weather. I'm thinking vacuum leak in one of the old hoses but it's stopped doing it for a while now.

Ever replaced the knock sensor?

 

Did you just slap a new TPS on it and go or did you adjust it the way the FSM says to do? If you don't have the FSM you can get it in several places online.

 

 

O2 sensor code could be a clue, even if it's for the rear sensor. ECU looks for a certain signal range on the rear sensor and it has to stay fairly steady. If the signal strays out of range the ECU may set a code for the sensor. This could be caused by an exhaust leak, a vacuum leak, a screwy fuel injector, a sticking valve, lots of things.

Much easier to check/replace the knock sensor first.

you mentioned cleaning the MAF but didn't say how.

 

You might try the SeaFoam - uh - foam/spray, with the u-shaped nozzle. Just thinking the IACV could be sticking or something like that.

Spark plug tube seals leaking oil? Pull the spark plug wire out, if its covered in oil replace the valve cover gaskets and the tube seals.

Did you ever solve this?