Chasing a power lag in 01 Forester

[AdventureSubaru]

Bought it with a busted CV etc and 240,000 miles for a song. New axle in and it drives nice. Engine idles smooth and trans shifts well. Now it seems I have one more bug to chase.

 

Intermittent power lag/bogging down. Shows up anytime but more consistently under load/steep hills. Power lags and will sometimes catch and accelerate normally again. Or, if you take your foot off the gas and reapply pressure, it's normal again.

 

The car had a few CEL codes originally - 3 different cylinder misfires and the generic misfire. I cleared those codes and they have not returned. During one test drive, the AT Oil Temp light began flashing and remained on until I parked the car.

 

So reading up it seemed that MAP/MAF, TPS and bad ground were most likely. Checked connections and replaced the TPS with a used one since I had some spares. No change. Pulled the MAP sensor and cleaned it up. No change. Added a ground cable from negative battery terminal to the AC bracket. Thought I was good to go but after about 10 minutes of driving it was back again.

 

May try a heavier gauge wire. What next? Replace MAP? plugs, wires, coil? Anything else. The AT light has not returned and there is no CEL.

[1 Lucky Texan]

look for oil in the spark plug tubes - might need valve cover gaskets. If the problem seems related to moisture/dew/rain, maybe plug wires.... both of those can throw misfire codes.

 

also, our cars don't like most plugs other than NGK - maybe prev owner threw some cheap plugs in it.

 

do you KNOW when it last got a timing service? Interference engine so, idlers and tensioner need to be in good condition. toothed idler often seizes or looses it's bearings and throws the belt off. $$$$!!!

 

AT fluid must be checked while idling - only fluid that's like that. Might try a fluid change - best if really nasty would be 3 drain/fills with a drive around the block between each one - that gets you 80-85% new fluid.

Edited February 1, 2016 by 1 Lucky Texan

[forester2002s]

Fuel-filter partially blocked?

[AdventureSubaru]

I'll probably throw some plugs and wires at it, but this is just a power lag, not a sputter like the hesitations I've felt on every car I've ever had that needed plug wires. Feels more electronic than that.

 

Fuel filter was a consideration. I do have a good used one that I may toss on. Without a CEL or anything it's pretty scattering trying to find the issue.

 

May go to the pick n pull and grab some sensors. Hate taking the shotgun approach but not much to go on yet.

[wtdash]

I'd check for STORED codes in the TCU/TCM

TD

[Fairtax4me]

Sounds like what a bad knock sensor will cause.

 

Also, is the MAP sensor mounted on the TB? That's not something that's normally cleaned.

[unibrook]

Does the bogging seem to happen most or always when engine warm as opposed to no problem when engine cold?  If so, your front 02 sensor prob needs replacing.

[Bushwick]

You REALLY need to do a full tune-up before trying to diagnose anything else. At a minimum, hand-gapped NGK pligs, wires, air filter, fuel filter, oil change, and might as well do a trans fluid as it's probably original, and while at it, suck out the power steering fluid and replace with fresh. Wouldn't hurt to replace ALL the vacuum lines too and timing belt.

 

It might very well have the same plugs and wires it had 120k miles ago, dirty air filter, etc. Plugs can be nearly dead and still run the engine, though you'll get erratic issues, not the least being excessive fuel usage, misfires, etc.

 

Do everything mentioned, reset the ECM, get it on the road and see where it's at. Probably $100 worth of parts at most plus whatever belt and idlers, tensioner run. You'll be at square 1 with everything being done, and won't be playing guessing games when it'll chomp the belt or is lacking power from excessively worn plugs.

 

If after doing all that it's STILL lacking power, then it's something more serious. 

Edited February 25, 2016 by Bushwick