Revving problem in 2.5 -->2.2 Outback swap

[Ruscy]

I have a 97 Legacy Outback. Before coming into my possession, it had 2.5 to 2.2 engine swap. It ran fine at first, but after a while, it began having a few problems.

 

It’s main problem is that it revs up to nearly 4000 rpm occasionally, on its own. It does this when in gear, or in neutral. It’s worst when I’m at a stop, clutch in, revving all out. It’s not such a problem at speed, though the engine still wants to get into that 3000+ rpm range. This becomes problematic on long down hills in residential areas. To not speed, I have to put the clutch in, and then off it revs again.

 

Another symptom (of the same problem?) is weak starts. Right after ignition, the engine can’t quite figure out where to idle, sometimes nearly puttering out. I gas it lightly, just tapping the pedal, and it revs, but delayed. Too much gas at this juncture will kill it. This starting issue goes away after about a minute, sometimes idling nicely, other times roaring off to above 3000 rpm.

 

At highway speed, it occasionally acts as though my foot slipped off the gas pedal, shuddering to a slightly slower speed, then picking up again. It does this repeatedly.

 

Sometimes, there’s no problem. Seems that after sitting all night, on the first start of the day, it will run fine. After that first drive, starting it up again after a short park, it’ll start acting up.

 

Took it in to a dealer to get a diagnosis. He said the engine has been swapped, the 2.5 computer doesn’t know what the 2.2 engine needs. He said my options are to replace the computer & wiring suite or the engine.

 

Dealer said it gave these codes:

PO117 Engine Coolant Temp Sensor Circuit Low Input

PO122 Throttle Position Sensor Circuit Range Problem

P0125 Insufficient Coolant Temperature for Closed Loop

 

We had replaced the throttle position sensor before taking it to the dealer. Right after the new TPS was was in, it seemed to have fixed the problem. But then it returned.

 

From what I gather from looking at this board, this swap has been done many times without this problem, and this Outback ran fine initially after the swap, then this problem came up. Anyone seen this before? Any ideas? Thanks.

[johnceggleston]

i don't really know, but i'd start by looking for a loose connection. a connector working loose over time would explain a lot of ills.

[hankosolder2]

I would be focusing on the coolant temp sensor and associated wiring. If the computer thinks the car is stone cold, it will be kicking it up into high idle. There are some large multi-pin connectors located on the passenger side of the engine/transmission junction. I would inspect those very carefully for corrosion, damage. Chances are your wiring problem (if there is one) is on the engine side. Perhaps the 2.2 engine and engine wiring harness was sitting in a junkyard outside or in a leaky shed and got wet...corroded connectors, etc. The sensor itself may be faulty.

 

The idle air motor may also be sticking.

 

Dealers don't know much about engine swaps, but I can assure it will run perfectly with the 2.5 ecm and matching parts. I have one so swapped which is sitting in my driveway!

 

Nathan

[subaru360]

Seems like your idle air control valve is gummed up and sticking. Clean it out real good with carb cleaner and see how it is.

 

The 2.5 computer will run the 2.2 engine just fine. It's a MAF engine and compensates. I do tons of these swaps. All the wiring is the same.

[Ruscy]

Hey, thank you for the replies. I'm sorry it's taken me so long to post again.

 

Checked the idle air control valve. seemed to be working fine, cleaned it out with carb cleaner anyway and put it back in.

 

Checked the coolant temp. sensor. The book said it should be getting approx. 5 volts from the ecu, mine was getting a steady 3.84. Is that anything to worry about? the sensor itself seemed to be working fine. with the ignition in the on position, when I hooked up the sensor...

 

...

 

just went out to remember what i did and double check. figured i'd do a test. disconnected coolant temp sensor, turned on the car with it disconnected. idled as it should! when i completed the circuit with the volt meter, with the car running, the engine revved up. hopefully that is my problem. we'll see tomorrow when i get the part. fingers are crossed.

[Ruscy]

Put in a new coolant temp. sensor, seems to have fixed it!

the check engine light even went off, which i Never expected to happen. hard to believe it was that simple. in hindsight, looking at those codes, they point right at it.

 

found this page very helpful:

http://www.lovehorsepower.com/SubaruDocs/CoolantTempSensor.html

 

hankosolder2, thank you very much.

 

hope i'm not posting on this thread again with another update.