Intermittent loss of power while engine is cold...

[George A.]

My 1.8L Subaru Impreza 1995 (manual, front wheel drive) recently
started to behave strangely:

When an engine is truly cold (mornings or driving home after
work), it starts and begins to drive normally, however, shortly
after that it tends to lose power for a moment or two, then
resumes OK, then these cycles repeat until an engine fully
warms up. Then it behaves perfectly O.K.

It's kind of difficult to describe. Basically, I press
accelerator and feel that it "does not work" - very little
(if anything) happens; then, as I continue to hold it down,
the car "wakes up" and finally responds and accelerates.
This usually happens at least several times, rather
unpredictably. It's as if the engine is not getting enough
fuel or air, or as if the mixture is not ignited in timely
fashion.

May or may not be related, I also noticed that, when the car
is in this state, it seems to idle strangely - an engine
shakes (I can feel the car shaking a lot more) and tachometer
goes up and down from high 1,000 rpm to about 100 (when warm,
it idles at approximately 400 rpm normally).

The car is up for some expensive maintenance and break job
pretty soon, so before I do any of it, I'd like to know
what might be the problem with the engine and how expensive
it might be. (I can, after all, buy another car, if it
does not make financial sense to fix this one).

Any ideas? Many thanks in advance.

George

 

[strchild]

When was the last time you did the basic tune-up or at least inspected your
plugs, wires, fuel filter, air filter, PCV, and anything anybody else can
think of for a basic tune-up. I wonder if this could be temp-sensor
related? Sounds similar to what my '93 was doing before I replaced the
plugs. Are you receiving any engine codes from the check engine light? 400
RPM seems low to idle at.

~Brian

 

[Carl 1 Lucky Texan]

When was the last time you did the basic tune-up or at least inspected your
plugs, wires, fuel filter, air filter, PCV, and anything anybody else can
think of for a basic tune-up. I wonder if this could be temp-sensor
related? Sounds similar to what my '93 was doing before I replaced the
plugs. Are you receiving any engine codes from the check engine light? 400
RPM seems low to idle at.

~Brian

Retrieving codes might help. The symtoms you report can relate to bad
MAF, bad TPS, bad IACV and even bad plug wires/coils etc.

Do the cheap stuff first or get someone to diagnose it when its in a
failure mode.

Carl

 

[Eeyore]

My 1.8L Subaru Impreza 1995 (manual, front wheel drive) recently
started to behave strangely:

When an engine is truly cold (mornings or driving home after
work), it starts and begins to drive normally, however, shortly
after that it tends to lose power for a moment or two, then
resumes OK, then these cycles repeat until an engine fully
warms up. Then it behaves perfectly O.K.

It's kind of difficult to describe. Basically, I press
accelerator and feel that it "does not work" - very little
(if anything) happens; then, as I continue to hold it down,
the car "wakes up" and finally responds and accelerates.
This usually happens at least several times, rather
unpredictably. It's as if the engine is not getting enough
fuel or air, or as if the mixture is not ignited in timely
fashion.

May or may not be related, I also noticed that, when the car
is in this state, it seems to idle strangely - an engine
shakes (I can feel the car shaking a lot more) and tachometer
goes up and down from high 1,000 rpm to about 100 (when warm,
it idles at approximately 400 rpm normally).

I'd advise in the first instance that you do the simple things like replace the
fuel and air filters plus spark plugs.

If somome can test fuel pressure too, so much the better. It might also pay to
add some injector cleaner to the tank or have the injectors professionally
cleaned ultrasonically.

Graham

 

[Eeyore]

When was the last time you did the basic tune-up

How do you 'tune up' a car with an ECU ?

Graham

 

[Eeyore]

When was the last time you did the basic tune-up or at least inspected your
plugs, wires, fuel filter, air filter, PCV, and anything anybody else can
think of for a basic tune-up. I wonder if this could be temp-sensor
related? Sounds similar to what my '93 was doing before I replaced the
plugs. Are you receiving any engine codes from the check engine light? 400
RPM seems low to idle at.

I certainly agree about the 400 rpm. It's only a 4 banger ffs !

Doesn't the Impreza have individual coils per plug too ? Worth checking them as
well.

Graham

 

[Scott Dorsey]

How do you 'tune up' a car with an ECU ?

Replacing plugs and filters mostly. No actual tuning involved any more,
but the price schedule still calls it a tune-up anyway.
--scott

 

[AS]

I think the filters would not change behaviour being hot or cold.

With the low, rough idle in mind, I would look into a cracked blow by
hose, vacuum leak, or defective connection in one of the sensors, in
particular MAF, temperature or TPS.

Plugs, wires and filters should be kept in good condition anyway, so it
would not harm if you changed them if you have not done so recently.

Good luck!

 

[AS]

Forgot to mention sticky EGR valve.