95 Legacy cold bogging and no throttle response.

[Hondaslayer]

Normally I am not one to be stumped on Subarus, especially EJ22's, but this one has me perplexed to say the least.

 

Vehicle: 95 Legacy :LSi 2.2 litre with 4EAT

 

Condition: On cold starts the engine will start fine and idle normally. Problem is when I attempt to give it gas. Touch the accelerator pedal and the engine RPM drops to 500 or lower. The engine does not stall, but the RPM do not climb at all. Release accelerator pedal and the idle returns to normal (albeit slightly rough)  Within a few minutes everything is fine and the car drives normal. Gas mileage is horrendous (11-12 mpg)

 

I cannot find any vacuum leaks at all.

 

Currently there is no CEL and vehicle just passed emissions with flying colors

 

Previously it had a code for a knock sensor (replaced with OEM sensor after cleaning mounting surface)

 

Timing belt is brand new (under 2,000 miles)

 

Cam sensor, crank sensor, MAF all swapped with known good units, no change. 

 

Coolant temp sensor is new, replaced when engine was out (replaced the typical 2.2 oil seals and timing belt) with new OEM sensor

 

Spark plugs and wires are new NGK

 

Fuel filter is new

 

Fuel pressure regulator seems ok (no fuel in vacuum hose)

 

Throttle position sensor is new and set to middle of spec (.50 IIRC)

 

Side note: When this is acting up the transmission binds badly. No binding at all when the car is up to temperature. When adjusting the TPS there was a buzzing noise like a solenoid actuating from the transmission. When this noise occured the TPS reading went way out of spec. I suspect something in the transmission (either duty solenoid C, or perhaps one of the solenoids in the valve body) to be failing and interfering with the TPS.

 

Either way, I'm at a loss and it's a very strange feeling.

 

Help?

 

 

-Ben 

 

[Bushwick]

Just going off your symptoms, sounds like something is shorting and grounding out something else.

 

When adjusting the TPS there was a buzzing noise like a solenoid actuating from the transmission. When this noise occured the TPS reading went way out of spec. I suspect something in the transmission (either duty solenoid C, or perhaps one of the solenoids in the valve body) to be failing and interfering with the TPS.

 

Sounds like you figured it out already. I'd inspect further to find out what's "buzzing" (solenoids can buzz) and either replace or inspect. If the trans is binding, I'd fix and also inspect the wiring just in case there is a short or something?

 

As for the gas mileage, do you have a brake caliper dragging? Is the air filter clean (can you see sunlight through ALL the rows??). People seem to ignore air filter changes and sometimes plugs, but these are important to get best MPG and healthy engine. Old O2 sensors can really hurt MPG, AND they can cause funky cold engine running if the preheater isn't working. I had a rear (downstream) O2 preheater fail, I ignored it, then the sensor eventually started shorting out internally and caused all sorts of havoc. Not saying it's definitely your problem, but it doesn't hurt to replace them, especially if old, and even more so if they get contaminated from say a bad head gasket or turbo failure. 

 

If it were me, I'd put a new air filter in and get some O2 sensors off rockauto for piece of mind. My MPG seems to be a touch lower than what others claim to get and the O2's are next on the list. Even if new ones only give you a 2% increase in gas mileage, they'll more than pay for themselves at the end of the year with the sky high gas prices.

Edited February 13, 2014 by Bushwick

[Fairtax4me]

I wouldn't worry about the buszing right now.

If you were playing with the TPS, you need to do two things.

 

First clean the throttle body bore and the throttle plate so the plate closes all the way.

Second put a voltmeter on the center pin of the TPS and adjust it until it reads 0.50V at closed throttle.

Then unhook the battery negative for a few minutes to reset the ECU.

 

The bogging issue could be a few things. Vacuum leak, Low fuel pressure, skipped timing belt.

How high is the cold idle RPM? Should be around 1,200-1,500 depending on outside temp. It should not be above 1,700. If cold idle speed is normal the ECT sensor is probably OK, but it wouldn't hurt to check the temp readout with a scanner if you have access to one.

 

If it hasn't had a fuel filter recently, replace that. If the filter is clogged it can reduce fuel pressure and cause it to run extra lean when cold.

 

Front O2 sensor will affect fuel mileage, but is not active when the engine is cold, so will not cause cold running problems.

[Hondaslayer]

Forgot to add, the front a/f sensor was replaced (oem) due to some idiot forgetting to disconnect it while dropping the exhaust

 

Air filter is new

 

Fuel filter is an interesting thought. The one on the car is new (replaced right before I bought it) but it's an aftermarket part. I was a bit leery of it, but there was no difference in fuel pressure when I bypassed it. I'm probably going to put an OE one on either way for piece of mind. 

 

Intake manifold / throttle body / IAC were thoroughly cleaned while off the car.

 

TPS is set at .50 (ish, second volt meter said .51, close enough, still in spec)

 

Cold RPM is 1500 - 1700 initially, dropping to 1000 then finally 750.

[Hondaslayer]

Perhaps my problem just diagnosed itself.........

 

Went out to start the car to go to lunch. *click* dead battery. Jumped car and pulled it into the shop to perform a charging system test. Battery was low, but still good. Alternator OTOH had excessive ripple. Excessive ripple eh? Funky voltage and potential introduction of AC into a DC system could very well cause all kinds of issues.

 

Good news, a new (reman) alternator is only $63 my cost. Bad news, I missed them by 15 minutes.

 

To be continued tomorrow (assuming they have one on the shelf)

[Hondaslayer]

To follow up.....

 

150 miles and 1 week later and still good.

 

 

This makes no sense at all, but the alternator may well have been the culprit.