Severe engine power loss betw idle and 2k RPMs

Hello,

A few days ago I was driving home from work and all my dash lights came on, so having read alternator-related posts on this board beforehand I went ahead and just ordered a new one from the parts shop and put it in. At about this same time, I have an extreme loss of power under medium and heavy acceleration if the RPMs are between idle and 2000 or so. If you mash the accelerator down, it lags around for a second or two then reaches 2000 RPMs and blasts off. In the same way that most SVXs feel cantakerous when cold, this is how it feels all the time between that rev range. Even at constant speed in overdrive, it is tough to pull hills.
I cleaned out the throttle body to see if that would help, but it is still there. I've read about the ECU crush mod, but that seems to apply only to acceleration and not to general power loss. I've searched and read a few other posts with my same symptoms, but no one ever posted a solution (except for the throttle body clean). The problem just seemed to happen all of the sudden. Any advice?

Thanks,

[UberRoo]

Pull the codes. Don't bang your head against the wall until you do.

I've seen bad spark plugs exhibit these symptoms more than once. If it's gutless below 2000 RPM even when you floor it, your TSP is probably not faulty, but if you suddenly have power once the accelerator pedal reaches a certain point, it's a likely suspect.

Also, possibly your IRIS valve isn't working.

[n00b on demand]

This acceleration lag problem is something i have been describing ever since i got my SVX back in Nov 2003. Except mine only happens when my a/c or defroster is on. And i also have the torque converter locking up at 50 MPH in 4th gear.

Originally posted by UberRoo
Pull the codes. Don't bang your head against the wall until you do.

I've seen bad spark plugs exhibit these symptoms more than once. If it's gutless below 2000 RPM even when you floor it, your TSP is probably not faulty, but if you suddenly have power once the accelerator pedal reaches a certain point, it's a likely suspect.

Also, possibly your IRIS valve isn't working.

I did check the codes, and all I have is a code 12 (starter signal), however it's been showing that one for months.

It's odd in the way that attempting to accelerate ends up slowing the car down (the RPMs sometimes drop). It seems like it might be an electronics or vacuum / valve issue. If I accelerate ever so gradually then I can eventually make my way up the tachometer and get up to speed; but until then it feels just like driving a cold engine in that rev range. I'll search for IRIS valve info; anything else to check? Plugs should still be good; changed 30,000 ago with Subaru stock.

[n00b on demand]

this problem sounds awfully familiar

[svxistentialist]

Garrett, mine is currently giving bad driving symptoms. It originally gave the codes for MAF sensor, and both oxygen sensors, left and right.

Having figured it could be drawing air, I tightened everything up that I could. It now only shows the MAF sensor code [23, I think] voltage outside the expected range.

In your case, I would suspect the TPS. Check the voltage is in the correct range, needs to be 0.5 volts or so. Also check it is not faulty across the range of the potentiometer. Do a search on TPS, there is advice on checking this.

You should also check for vacuum leaks, and suspect the MAF as well. Tighten up all manifold pipes, including the small-bore fuel pressure regulator vacuum line on lhs, to eliminate this possible fault first.

Best of luck,

Joe

[UberRoo]

You're right; the plugs should be good, but 30k miles is quite a few. I hate to send you down the wrong track, but it's still very possible that it may just be plugs.

Does it behave this way in neutral, i.e., when there's no load on the engine?

I have no idea what you're talking about when you say it behaves like a "cold engine." My car is slightly lethargic when cold, but this seems mostly due to shifting behavior. I really have no "cold engine" behavior to speak of.

Another possibility, though somewhat outlandish, is that in a particular gear (second maybe) the clutches in the transmission are working against each other. I'm not sure how likely this is, but I reckon it's very possible. I'd have to study up on this to figure out how that would work. As soobiesvx93 suggests, having your torque converter lock up at the wrong time would do the trick. Pull the transmission codes too if you haven't already.

You might try manually shifting the car when it does this. Just moving the shifter to third for a split second will completely disable the torque converter lock up, and will also momentarily release the overrunning clutch. Anything you can do to get the transmission to hiccup might help overrule an engine-related problem. ...although I think you're probably already on the right track.

The fuel filter may be plugged. Some systems have a pressure relief valve that will release when demand for pressure is high enough. Fuel filter problems have a tendency to exhibit strange symptoms.

svxistentialist mentioned vacuum leaks. That a very good point. Normally they affect the engine's idle, but this isn't always the case. It is however very common for vacuum leaks to "go away" at higher engine speeds, as they don't leak as much under low vacuum and bleed proportionately less air at those speeds anyway.

A few more off hand ideas: A hydraulic lifter may not be pumping up at low revs. A burned valve may reduce pressure enough to prevent combustion. Your engine may have a loose connection that comes and goes as the engine rocks back and forth inside the engine bay under torque - which there isn't enough of below 2000 RPM.

[n00b on demand]

in my case i have never gotten any lights from the dash. It just happens when the a/c or defroster is on. I always drive using "3" because i drive mostly in the city so the torque converter only locks up when im in "d".