rough idle and odd hesitation

[Chef]

92 subaru legacy auto NA

I try to start my car, and it takes quite a number of turns and a little gas to do so. Then, it idles very roughly, feels like it's missing. It hesitates upon acceleration. Once the RPMs are at 2000 and above, it runs smooth again. I tried pulling spark plug wires to see if I could find one that doesn't seem to make a difference, but it's hard to tell. One MAY appear to make no difference, but I can't tell really.

This used to occur to me once in a while when the car has been sitting for a half day or more, except that it would smooth out on it's own within a minute or two.

All the plugs are sparking. I replaced the fuel filter a few months ago. I suspect a problem with one injector, but I'm not certain. The missing certainly makes it appear as though it is one or two cylinders mis-firing, and therefore not likely a fuel pump problem.

Any info would be appreciated.

Chef

[Legacy777]

How does it run when it's warmed up?

I'd lean towards the coolant temp sensor being the issue.

[Chef]

Well, about after I posted this yesteday, I decided to take a drive to see how it moved at higher rpms. It lacked power throughout the range even if it smoothed out. the hesitation was a consistent thing while driving, not jerky intermittant cuts.

However, after a few minutes of driving with a heavy foot, it began to slowly smooth out, and then suddenly all zip was back. It's been fine since.

There is obviously a problem still, but an intermittent one (of course... ) I will look into the coolant temperature sensor - thanks for the suggestion Josh.

BTW, how often does this cause intermittent problems as opposed to consistent ones?

[scuzzy]

if the cts is going out and it's reading a higher temp than what the engine actually is, it'll make the ecu think the engine is warm when it's really not. a warm engine requires less fuel to idle and run properly, a cold engine requires more.

[douglas vincent]

Replace the positive battery connection completely and get new plug wires.

I have the same problem with my wifes sedan. Just have to do the battery connection now.

[Chef]

Good information all around. thanks for the replies, I will look into these.

[LegacyPunk]

if the cts is going out and it's reading a higher temp than what the engine actually is, it'll make the ecu think the engine is warm when it's really not. a warm engine requires less fuel to idle and run properly, a cold engine requires more.

So thats why it would cause all that trouble, because when the engine first warms up it idles higher right?.....I hate stupid little sensors.

[Manarius]

So thats why it would cause all that trouble, because when the engine first warms up it idles higher right?.....I hate stupid little sensors.

No, it idles high because the choke is set. Tap the gas and it'll stop doing that..I do it all the time.