Engine idle ok, 1100 rpm, "drive" engaged and car stopped, rpm's jumping from 600 to 900 and engine runs rough. In cruise the engine is smooth again, keeping rpm's at 1200 with 50 Miles speed. What might be the problem?thanks for your answer.
SOURCE: rough idle stalls at low rpm's
hello first check your idle with the car running foot on brake see were your rpm reading is if your below 500rpm check your label underhood for your curb idle setting second see if theres a adjustment screw you can increase were your gas cable lever rest against your set screw underhood if you feel confident enough remove your iac motor idle air control valve if the bore were the end of the pintle extracts out to close has varnish builup our carbon it will stick creating vacuum leak type senario causing stalling rough idle sometimes even no start conditions good luck
SOURCE: Blazer runs rough when running at 45 to 55 mph
the problem was low transmission fluid. added half a quart and the problem went away.
this sounds similar to a problem i had.
as the rpm went over 2000 the engine would stop for a split second and then kick back in.
after a few days looking my garage finally found the problem was a faulty air mass meter.
this cost me £200 in total to be repaired.
SOURCE: 2001 Forester, Rough idle and engine loping driving at low rpm
I had a similar problem on my 2002 Impreza RS 2.5 (same engine and engine control system). In my case it was the O2 sensor on the intake manifold. This happened at 34,xxx mi. so it was covered by the warranty. Replacing the part is very easy. (two bolts and a wiring harness). Obviously I would start simple and cheap and work your way to expensive and difficult.
From my understanding its all caused from the engine missfiring. If its been a while or never, I'd change the spark plugs first. (stick with the Subaru Parts plugs, I went after market and the dealer claimed the plugs were not the correct "temperature" and had to pay for the new plugs and install although they did it without my permition. Thats a whole nother story).
Could also be the manifold pressure sensor.
Either 02 or manifold pressure sensor may cause intermitent check engine light.
Where I live Brookline,MA , Autozone will run a free diagnostic on your car by hooking up to your ECU and will give you the trouble codes and possible remidies. Of course there are no guarentee's but it will point you in the right direction.
Good Luck
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